GCSE Physics Paper 1 Revision

Physics Paper 1 Last Minute Revision 2026 Edexcel GCSE Combined Science

Estimated read time: 1:20

Summary

This revision video is a fast-paced run-through of Edexcel GCSE Combined Science Physics Paper 1. It starts with the three core practicals: investigating acceleration, wave speed in liquids and solids, and refraction in glass blocks. It then moves through motion and forces, including scalars and vectors, speed, acceleration, and graph skills for distance-time and velocity-time graphs. The video also revises Newton’s laws, momentum, centripetal force, stopping distances, and reaction time, before covering energy stores, pathways, Sankey diagrams, efficiency, heating, and energy resources. The second half focuses on waves, the electromagnetic spectrum, radio waves, and then radioactivity: atomic structure, Rutherford’s experiment, isotopes, types of radiation, nuclear equations, half-life, and radiation safety. It’s packed with exam tips, formula reminders, and common mistakes to avoid, making it a compact last-minute checklist for Paper 1.

Highlights

Core practical 1: measure acceleration using light gates, a stopwatch, and a changing mass setup ⚙️
Ripple tank practical: use a ruler, stopwatch, and wave equation to find wave speed in a liquid 🌊
Refraction practical: ray box, glass block, and angles measured to the normal 🔦
Distance-time graph gradient = speed, velocity-time graph gradient = acceleration 📊
Area under a velocity-time graph = distance travelled, even for triangles and rectangles 🧮
Resultant force = add forces in the same direction, subtract in opposite directions 🧲
Stopping distance = thinking distance + braking distance, with different factors affecting each 🚘
Momentum = mass × velocity, and collisions follow conservation of momentum 💥
Sankey diagrams show useful and wasted energy with thicker arrows for larger amounts 🔺
Electromagnetic spectrum order and uses/dangers are exam favourites, especially gamma to radio 📡
Rutherford’s results proved the atom is mostly empty space with a small positive nucleus 🧪
Half-life questions often ask you to halve activity repeatedly and read from graphs ⏳

Key Takeaways

Base core practical answers on the relevant equation first — that’s an easy marks boost 📘
Know the difference between speed, velocity, distance, displacement, and how to read graphs correctly 📈
Newton’s laws and resultant forces are all about balanced vs unbalanced forces 🚗
Momentum and stopping distance questions love real-life examples like seatbelts and crumple zones 🚦
Energy questions usually want stores, transfers, efficiency, and waste reduction 🔋
Waves and the EM spectrum need definitions, uses, dangers, and wavelength/frequency order 🌈
Radioactivity is all about atomic structure, decay rules, half-life, and protection from exposure ☢️

Overview

This video is designed as a last-minute exam boost, with a heavy focus on what Edexcel GCSE Combined Science Physics Paper 1 tends to ask. The opening section is especially useful because it turns the three core practicals into easy mark-scheme style answers: start with the equation, identify the measurements it tells you to make, then explain the equipment and procedure. That approach repeats across acceleration, wave speed in liquids and solids, and refraction.

The middle of the video is a solid revision sweep through motion and forces. It covers scalars and vectors, speed and acceleration calculations, graph interpretation, Newton’s laws, momentum, and stopping distances. The presenter keeps tying each topic back to exam wording, which helps with those longer six-mark questions where the marks depend on precise definitions and clear reasoning.

The final sections move through energy, waves, the electromagnetic spectrum, and radioactivity. There’s a strong emphasis on recalling definitions, remembering the order of the EM spectrum, and comparing radiation types by ionisation and penetration. The half-life and nuclear decay parts are especially exam-friendly, with repeated reminders about balancing equations, reading graphs carefully, and using shielding, distance, and time to reduce risk.

Chapters

00:00 - 10:00: Core Practical Skills and Measurements The chapter introduces exam-focused advice for core practical questions, emphasizing that answers should be built around the relevant calculation first and then matched with the correct measurements and equipment to earn marks.
10:00 - 20:00: Motion, Speed, Acceleration and Graphs This section explains motion formulas and graph basics: using the speed = distance/time triangle to rearrange equations, recalling typical everyday speeds, and interpreting distance-time graphs where gradient represents speed (steeper means faster, flat means stopped). It also shows how to calculate speed from the gradient between two points, giving an example that produces 20 m/s, and introduces acceleration as change in velocity per second with units of m/s².
20:00 - 30:00: Forces, Newton’s Laws and Stopping Distance The chapter explains how force, mass, and acceleration are related: a larger resultant force causes greater acceleration, while a larger mass causes smaller acceleration when force is the same. It also revisits Newton’s laws, showing that zero resultant force means an object stays at rest or continues moving at constant speed and direction, while unbalanced forward or backward forces cause acceleration or deceleration. Newton’s third law is introduced as equal and opposite forces between interacting objects.
30:00 - 42:30: Energy Stores, Transfers and Resources This section explains energy efficiency using a light bulb example: efficiency is useful energy out divided by total energy in, and percentage efficiency is found by multiplying by 100. It also covers ways to improve efficiency by reducing wasted energy, such as lowering friction, using insulation to reduce heat loss, and using thick low-resistance wires. It defines conduction, convection, and radiation, then introduces kinetic energy as the energy of moving objects and gives the formula KE = 1/2 mv².
42:30 - 55:00: Waves and the Electromagnetic Spectrum Covers the electromagnetic spectrum, including the order of waves by wavelength and frequency, and key facts such as red and violet limits in visible light. Explains how radio waves are produced by oscillating currents in circuits and detected by aerials, plus how reflection and refraction in the ionosphere allow long-distance radio communication, while microwaves are used for satellite links due to their shorter wavelength.
55:00 - 67:30: Atomic Structure and Radioactivity This section explains the key properties of alpha, beta, and gamma radiation, including their relative ionizing power, range in air, and what materials stop them. It then introduces radioactive decay and how to balance nuclear equations by conserving mass number and atomic number. The transcript walks through alpha decay, showing that an alpha particle contains two protons and two neutrons, so mass number decreases by 4 and atomic number decreases by 2.

Physics Paper 1 Last Minute Revision 2026 Edexcel GCSE Combined Science Transcription

Segment 1: 00:00 - 02:30 Right, this is the video you've been hoping to find. Without doubt, this video will help you to level up in your physics exam. This one's for the physics paper one Edexcel, but as long as you watch the physics video for paper two, if you're studying for any of the other exam boards, these videos will help you as well. Because the physics that you get taught, regardless of which exam board you're sitting, is all very, very similar. So, first let's start with the three core practicals that you'll get on paper one. So, core practicals always base your explanation on a calculation. Because the calculation will tell you what you need to measure. Then you just need to say what equipment you'll use to make those measurements, and then add any extra details if you need to, depending on the context. So, core practical one is investigating acceleration. And the question could be, "Explain how you would carry out an experiment to determine how mass affects acceleration." Six marks. Okay, so how does mass affect acceleration? Model answer. Base your explanation on the calculation. So, if it's for acceleration, acceleration is the change in the velocity divided by the time. So, this formula tells you you're going to need to measure the change in velocity. So, you get one mark for saying that, one mark for saying that. One mark for saying that. How are you going to get the velocity? Well, you need to measure it with two light gates. If they do ask, you say this first light gate here is going to measure the initial velocity when you first let the trolley go down the ramp. And this second light gate is going to measure the final velocity.
Segment 2: 00:00 - 02:30 And that's how you'll get the change in velocity. We also need to measure time for your fourth mark, with a stopwatch for your fifth mark, and then any of this extra context detail. Add mass to the trolley and drop the weight to pull the trolley down. So, this is your weight here. And that's going to as that falls, it's going to pull the trolley across. Add more mass to the trolley, repeat, and compare results. So, it's to see how does mass affect acceleration. So, they start with a little bit of mass on there and then get more mass. And uh make sure the ramp is slightly
Segment 3: 02:30 - 05:00 tilted, so it'll cancel out friction. You'll get a mark for seeing that in the exam as well. So, you don't want the ramp to be so tilted that the trolley starts to accelerate even before you've dropped the weight. You want the trolley just to move at a steady velocity. And that'll get you your six marks for that. Core practical two, investigate getting waves. So, if you don't get the last core practical, you could get this one. Now, it actually comes in two parts, and the first part is something like explain how you would carry out an experiment to determine the speed of waves in a liquid, six marks. So, once again, base your explanation on the calculation. So, it's to do with a ripple tank, and you've got this little vibrating uh piece of wood. It slaps the water and creates waves going across the top. Get a light to shine down, and it projects shadows of the waves on the bottom down here. Uh make sure you've got a ruler under here, so that if you're going to take a photo or a video, you'll be able to pause it, and you'll be able to see the shadows against the ruler, and that'll help you to measure the length of the waves. So, if we're going to get the wave speed, the formula we need is frequency times by wavelength. One mark for that. So, I'll tell the examiner for a mark, measure the frequency. Make sure they know that you know what that means. So, by counting how many waves there are in 1 second. Um using a stopwatch. And measure the wavelength. By measuring from wave peak to the next wave peak. So, you're letting them know that you know what wavelength is. And do that by using a ruler. Now, if they ask for more information, you can say, make the frequency more accurate by counting how many waves in 10 seconds, then dividing the number of waves by 10.
Segment 4: 02:30 - 05:00 To get how many waves there are in 1 second. Make the wavelength more accurate by counting how long 10 waves are, then dividing length by 10. So, just say 10 waves were 30 cm, then that would mean that each wave was 3 cm. >> [snorts] >> Another way you could do it is use a mobile phone to film the waves in slow motion. To get the frequency. So, you
Segment 5: 05:00 - 07:30 could see how many waves come out. And say 10 seconds once again. And then divide that by 10. So, if 17 waves came out in 10 seconds, do 17 waves divided by 10 seconds, that comes out as 1.7 waves per second, which is 1.7 Hz. And you could take a photograph of the waves with the ruler in the foreground to get the wavelength. You'll be able to zoom in, you'll be able to see where one wave starts, then where the next wave starts. And the distance between that is the wavelength. So, there you go. That's how you get your six marks for that. Now, the second part of that same core practical is explain how you would carry out an experiment to determine the speed of waves in a solid for six marks. So, it's this experiment here, where you basically take a hammer and you hit this end of a suspended metal rod and you'll get a high-pitched sort of frequency sound. So, once again, if we're going to get the speed, base your explanation on the calculation. >> [clears throat] >> So, the wave speed is the frequency times by the wavelength, once again. So, tell them measure the frequency. Read the frequency up on your phone. Measure the wavelength by measuring the length of the metal rod with a ruler and then you multiply it by two. So, they'll tell you that in the exam. But, yeah, the wavelength is basically twice as long as the metal rod. So, if that metal rod was 0.6 m long, then the wavelength would be 1.2 m. And for another mark, possibly, uh you say hit the end of the metal rod with the hammer and use your frequency up to record the frequency. So, each thing here is how to get a potential mark. >> [gasps] >> Core practical number three is investigating refraction. So, they'd say tell us how you'd carry out an experiment to get the refraction
Segment 6: 05:00 - 07:30 of a glass block. So, refraction is when the waves change direction at a boundary >> [clears throat] >> due to a change of density. So, use a ray box to shine a beam of light into a glass block. That's for one mark. Note the angle of incidence. Now, don't just leave it at that. You have to say between the normal and the incident ray. So, you have to explain where the angle
Segment 7: 07:30 - 10:00 of incidence is. So, that's the normal and this is the incident ray coming in. Then you'll need to note the angle of refraction [clears throat] between the normal and the refracted ray. So, this is the refracted ray here and that is the normal. So, this little angle there is the refracted ray. Now, if you don't say three and five, you won't get the marks quite often. >> [clears throat] >> And number six, compare the angle of incidence to the angle of refraction. Now, if they do ask other questions like how do you know that the wave is going faster? Well, F A S T is what I've made up. So, if the wave goes faster, it'll bend away from the normal. So, you can see down here, the wave must be going faster cuz it would bend away from the normal. If I was to just draw another normal in there, you can see that this angle here is bigger than this angle here. So, that wave there must have sped up as it came out because it bent away from the normal. And this wave here, as it's came in, must have slowed down because it's bent toward the normal. So, if it goes slower, it's bent toward the normal. So, there's a couple of extra top tips for you. >> [sighs] >> Right, let's get into the content. So, first, motion and forces. So, what are vectors and scalars? So, these are all common questions that you'll get in your exam. Remember, every time that you get an extra three marks, you jump up a level. A scalar quantity has size only. A vector quantity has size and direction. Examples of scalars and vectors. So, S for scalar, S for speed, V E for vector and V E for velocity. That's always the ones I go for. And speed and velocity
Segment 8: 07:30 - 10:00 are equivalents. So, velocity is the vector that goes with speed. Distance and displacement are tied together. So, basically displacement is distance but with a with a direction as well as a size. And there's other ones there as well. Make sure you know at least a couple of scalars and a couple of vectors. How do you calculate speed? So, speed is distance over time. You're getting given
Segment 9: 10:00 - 12:30 all the formulas this year, but in the following years you may not. So, make sure you know formulas. If you've got to rearrange equations, so what if it asks you to get the distance for example? Well, do your magic triangle. So, if speed equals distance over time, draw your triangle like that. Um distance is on the top shelf in here. And then speed and time must go there. Cover up what you're looking for. So, if you're looking for distance, cover it up. And what you're left with, speed times by time, is how to get the thing you were looking for. Typical speeds, just in case it's a multiple choice question. Walking is 1 and 1/2 m a second. Jogging is twice that, roughly at three. Then you've got running at four, and then cycling about six. Distance-time graphs. So, the gradient of a distance-time graph tells you the speed. So, if you've got a steep gradient like that, imagine that you are rolling down the hill, you're going to be going fast because it's a steep slope. If the slope is not as steep, then that's just going to be slow speed. And if the slope is flat, then that means the object has stopped. Now, don't get your distance-time graph mixed up with a velocity-time graph. >> [gasps] >> How to calculate speed from the gradient of a distance-time graph? So, what's the speed between points B and C? So, first of all, how far uh how much time has gone between B and C? Well, it started at 3 and it finished at 6. And how much distance? Well, B started at 10 and it finished at 70, so it's traveled a total of 60 m. And it did that in 3 seconds. So, if the object's moved 60 m, it took 3 seconds for that distance. Speed is distance divided by time. So, that's 60 m divided
Segment 10: 10:00 - 12:30 by 3 seconds. And that's 20 m/s. What is acceleration? Acceleration is a change in velocity per second. How to calculate acceleration? Well, it's the change in the velocity divided by time. So, change in velocity per second. Make sure you get the units of acceleration, which is meters per second squared.
Segment 11: 12:30 - 15:00 If you have to calculate acceleration, it is actually related to distance as well as related to time. This is the formula that you have to find in your formula sheet. You will be given it. So, it's the final velocity squared take away the initial velocity squared equals two times by acceleration times by the distance. Sometimes they'll use X for distance instead of D. Make sure that you square your values. Velocity time graphs. So, the gradient this time is acceleration. If you've got a steep slope, that means it's a big acceleration. If you have a slope that's a bit smaller, you'll have a smaller acceleration. And if it goes completely flat this time, it means there's no acceleration. But please make sure you know that it's still actually moving at a constant velocity. Cuz whatever the velocity is, it's certainly not zero. And that is what people make a mistake if you confuse your velocity time graphs with your distance time graphs. If the graph goes down, that means it's deceleration because it's slowing down rather than speeding up. And once it hits this bottom part, at that point, you've got zero velocity. How to calculate acceleration from the gradient of a velocity time graph. So, it's similar to how I just showed you, but it's a velocity time graph, so the gradient is acceleration rather than distance time graph where the gradient was speed. So, once again, if we want to know the acceleration between two points, just make sure you draw your little triangle between those two points, see how much it's changed on the Y axis. So, again, it's gone from 10 up to 70, so that's 60. How much has it changed on the X axis? That is three. And then you just do your Y axis divided by your X axis.
Segment 12: 12:30 - 15:00 So, change in velocity would be 60 / 3, which comes out as 20 m/s². How to work out the distance traveled on a velocity time graph. It's the area under a velocity time
Segment 13: 15:00 - 17:30 graph that tells you the distance traveled. So, if you've got a velocity time graph and it's a straight line because it's traveling at a constant velocity, you're going to get a shape that looks like either a square or a rectangle. So, how do you get the area of a rectangle or square? It's basically the base times by the height. So, the base is 10 and the height was seven. So, 10 times by seven is 70 m. What if it's a steady acceleration? This time you're going to get the area as a triangle. So, the area of a triangle is a half times by the base times by the height. So, a half times by the base goes from zero to 10 and the height went from zero up to seven. So, half times by 10 times by seven and that comes out as 35 m. How to work out the area of a complex shape? Okay. So, let's just say that the object was accelerating at first, then it goes into a steady velocity. So, this shape can be broken down into a triangle and a rectangle. And it is simple as that. So, now we just need to know what is the area of the triangle. Well, it's a half times by base times by height. So, it's a half times by five times by 10 and that comes out as 25. And then we need to add that to the area of the rectangle. So, that's going to be the base. Now, the base goes from five to 20. So, the base is just 15. And the height is 10. So, the height is 10. So, 15 times by 10 and that comes out as 150. Now, remember to add it together cuz the total area is the total distance traveled. So, that's the triangle plus the rectangle. 25 plus the 150 and that's 175 m. There we go. How to represent forces. So, forces are vectors. They are represented by arrows.
Segment 14: 15:00 - 17:30 The length of the arrow shows us the size of the force and the direction of the arrow shows us the direction of the force. For example, this here could be 10 N to the right, in which case this here will be 5 N to the right because it's only half as long. And it's still pointing to the right.
Segment 15: 17:30 - 20:00 This arrow here will be 5 N to the left. It's the same length as that arrow, but it's pointing left. What is a resultant force and how do you calculate it? So, a resultant force is the total force from two or more forces acting on an object. It's found by adding forces if they act in the same direction or take away forces if they act in opposite directions. For example, so if you've got this uh block here, you've got 3 N to the left and 5 N to the right, you're going to end up with 2 N to the right. It's basically tug-of-war. This team over here is won uh by 2 N compared to this team here. What about this? If this was tug-of-war, uh this team pulling to the left is winning by 4 N. So, uh force is a vector. Make sure you say the size and make sure you say the direction for two marks. This here is uh they've canceled out. 4 N and 4 N, so 0 N and no direction. This one here, now be careful. All right. That's 2 N to the right and 3 N to the right. So, we're going to add them together because they're going in the same direction. So, that's 5 N to the right. So, it doesn't matter which side it's getting pushed or pulled on, just pay attention to the direction of the arrow. Same again here. 3 N and 4 N, are they working against each other or with each other? They're working with each other in the same direction. So, that's 7 N right. And and this one here is 3 N to the left. Newton's first law. So, Newton's first law of motion states that an object will remain in the same state of motion unless a resultant force acts on it. In other words, if all the forces acting on it are balanced, then the object will keep doing what it's doing. So, if it's stationary and the forces are balanced,
Segment 16: 17:30 - 20:00 it'll stay stationary. If it's moving and the forces on it are balanced, it'll be moving with a steady speed. Newton's second law. So, Newton's second law explains the relationship between force, mass, and acceleration. It's the only one of Newton's three laws that's actually got a formula. So, force is mass times by acceleration. F = M * by
Segment 17: 20:00 - 22:30 A. What does it basically mean? The bigger the resultant force, the bigger the acceleration. So, both of these cars are the same mass. This car's got a big force, and that one's got a small force. So, the bigger the force, the bigger the acceleration. Because the mass of each car is the same. And if we have two objects and the force is the same, so you've got two forces the same, but this car is got a big mass and that car's got a small mass, then the bigger the mass of the object, the smaller the acceleration. Bigger the mass, the smaller the acceleration. Just think about if you're pushing your friend if he's on a sledge. If he's got a big mass, then it'll be difficult to make him accelerate. If he's only got a small mass, he'll accelerate very fast. What happens to an object when there are balanced or unbalanced forces on it? So, with these four examples, we should be able to explain any scenario. So, if the object at the start is at rest and the resultant force on it is zero, Newton's first law says the object will just stay at rest. If the object is already moving and the resultant force is zero, then Newton's first law says, it's going to keep doing what it's doing. So, that you'll get the same speed and the same direction. >> [snorts] >> What if you've got an object that's moving and there is a resultant force going forwards? Well, it's going to start to accelerate. What if you've got an object that's moving and there's a resultant backward force? Well, that's going to start to slow down. It's going to decelerate. Newton's third law. Newton's third law states that whenever two objects interact, they exert equal and opposite forces on each other. Mass and weight. Mass and weight are not the same thing.
Segment 18: 20:00 - 22:30 Mass is the amount of substance in an object. The units are kilograms. Weight is a downward force that acts on a mass when it's placed in gravity and the units are Newtons. How to calculate weight. Weight is mass times by gravity. Make sure you know that the gravity on Earth is 10 Newtons per kilogram. What are thinking distance, braking distance and the factors affecting them? The total stopping distance is going to be the thinking distance plus the braking distance. The thinking distance is the distance you travel while thinking about pressing
Segment 19: 22:30 - 25:00 the brakes. Now, you can't say it's the distance you travel during your reaction time. The braking distance is the distance you travel once the brakes have been pressed. So, for example, if a cat jumped out in the middle of the road, your brain would tell your foot to press the brakes. So, the distance that you travel while you are reacting to press the brakes, that's the thinking distance. Now, once you've actually pressed the brakes, the car has to mechanically come to a stop. So, the distance you travel once the brakes have been pressed, that's your braking distance. Now, you might get asked what are the factors that increase the thinking distance. So, it's basically anything that affects your reaction time and how long you're going to think for before you press the brakes. So, if you've been drinking alcohol, taking drugs, if you're distracted, if you are tired, they are going to affect the thinking distance. So, is traveling at a faster speed. However, that won't affect your reaction time. So, your reaction time will still be whatever it is, but in that time, you will actually travel further because you're going faster. Factors that increase the braking distance. Now, this is anything to do with the car. So, if you've got worn out brakes or tires, if you're driving in poor weather such as rain or ice, if there's a poor road surface such as gravel, if your car's heavier, or once again, if you're traveling at a faster speed, they are going to make the braking distance increase because there'll be less friction between the tires and the road. That is what you see. Typical human reaction time and how to measure it. Now, this hasn't came up for a while, so we could get this.
Segment 20: 22:30 - 25:00 Typical reaction time of a human is about a quarter of a second, and we usually use computers to measure the reaction times because it's so fast. A reaction time is the time it takes to respond to a stimulus. What do you mean? Right, so just say a computer turns on a light. The light would be the stimulus. The human has to quickly press a button to turn the light off. Now, pressing the button is the response. Now, the time taken between the light turning on and the human pressing the button, the response, to turn the light off, is the reaction time. And you could get up to four marks for saying something like that. Momentum. Now, this is higher
Segment 21: 25:00 - 27:30 only. If you're higher only, you'll want to watch these. If you're foundation, just put the video on fast forward. So, momentum is a measure of the tendency of an object to keep moving. Or, you can say momentum is a measure of how hard it is to stop an object moving, like once it is moving. How to calculate the momentum. So, momentum is mass times by velocity. Now, it's got very funny units. It's kilogram times times by meters per second. So, kilograms meters per second. Make sure you know that unit because you can often get one mark for saying that. What happens to momentum during collisions? So, during a collision, the law of conservation of momentum applies. What do you mean? So, it means the total momentum before the event, the collision, equals the total momentum after the event. So, that would be the mass that you've got at the start times by the velocity at the start is going to equal the mass at the end, after the collision, times by the velocity at the end of the collision. What is centripetal force? >> [sighs] >> A centripetal force causes objects to travel in a circular path. The force acts towards the center of the circle. So, you've got this centripetal force. What it actually does is it creates an acceleration towards the center of the circle, and that keeps the object moving in a circular path. Now, there's three types of centripetal forces: tension, friction, and gravity. Impact force. What are the dangers caused by large decelerations? Large decelerations on an object can cause damage. If the object is alive, this can cause injuries and even death. How can the hazards of large decelerations, so how can the hazards of large impact forces be decreased? Make the change in momentum happen over a longer impact
Segment 22: 25:00 - 27:30 time to decrease the impact force. So, how do you increase the impact time? Well, in cars we use seat belts, airbags, crumple zones, and suspension. If you're running, we use shoes with foam soles. How to calculate the impact force? Do the change in the momentum divided by the how long it took for that change to happen, and that'll tell you how big the force is going to be. Moving on to energy. There's 10 main types of energy.
Segment 23: 27:30 - 30:00 Now, there's a mnemonic here, His Majesty's neck and legs. Each letter stands for a type of energy. So, H is heat, you got magnetism, light, electrical, gravitational, sound, nuclear, elastic, chemical, and kinetic energy. Now, of those 10 main types of energy, only eight of them can be stored. So, there's another mnemonic, 8 kg of cement. Now, I've had to change H to T for thermal instead of heat to make the mnemonic work. >> [snorts] >> Now, basically, the only energies that can't be stored is light and sound from the list you've just saw. What's the law of conservation of energy? Energy can't be created or destroyed, it just gets transferred from one store to another. In other words, energy in equals energy out. The four energy pathways for transfers to happen. So, energy can move between the eight energy stores using pathways. There are four energy pathways, and we can remember them with a mnemonic for Mr. HE. Mr. HE, so M mechanical. So, you can transfer energy from one form to another mechanically. In other words, using a force, use radiation such as light, sound, infrared, things like that. Heat, transfer energy via conduction through contact and things like that. And we can also do work electrically. There's lots of gadgets we've created to transfer energy from one form to another. Like a bulb transfers energy from electrical energy into light. Know how to represent energy transfers using Sankey diagrams. So, energy transfer diagram, what we've got is the energy in will be drawn on the left. The energy out is drawn on the right. This top arrow here will be the useful energy. It should be anyway. And this bottom arrow should be the wasted energy. But, always keep an eye on the type of energy it is. If you know it's a bulb, then you know the useful
Segment 24: 27:30 - 30:00 energy will definitely be light and you do not want the heat. So, the heat is the wasted and the light was the useful. Now, what goes in must come out. So, 20
Segment 25: 30:00 - 32:30 and 100 have came out. So, that must mean how much went in must have been 120 J went in. Now, the bigger the energy, the thicker the arrow. So, we're going to have a nice thick arrow there. That represents 120 J. Over here, it's only 20 J. So, proportionally, try to make this arrow the correct thickness. This should be 1/6 as wide as that. And this arrow here should be 5/6 as wide as what the original arrow was. As long as it's roughly correct, that is fine. What does efficiency mean? Efficiency means it doesn't waste much energy. In other words, you get lots of useful energy out. For example, an energy-efficient light bulb gives lots of light energy out and not much energy is wasted as heat. How do you calculate efficiency? Efficiency is useful energy out divided by total energy in. If you want to convert efficiency into percentage efficiency, multiply by 100%. Here's an example to calculate the efficiency. What is the efficiency of the light bulb? Well, the useful energy out was 20 and the total energy in was 120. So, 20 / 120 = 0.17. And if they ask you what's the percentage efficiency, just take that value and multiply it by 100. So, that's 17% efficient, which is terrible. How do we improve efficiency? To improve efficiency, you have to have more useful energy and less wasted energy. You can reduce the wasted energy by reducing friction, such as by using a lubricant, by reducing heat loss, such as using an insulator to keep hot things hot, and to stop electrical wires from getting hot by using thick wires with low resistance. What are conduction, convection, and radiation? Conduction is a transfer of heat in solids. Convection is a transfer of heat in fluids. And radiation is a transfer of heat that
Segment 26: 30:00 - 32:30 does not require particles, i.e. , can happen in a vacuum, which is a posh word for empty space. What is kinetic energy and how do we calculate it? Kinetic energy is the stored energy that a moving object has.
Segment 27: 32:30 - 35:00 For example, if a car's moving, it has a store of kinetic energy. How do you calculate kinetic energy? 1/2 times by mass times by velocity squared. So that's a half times by m v squared. Now make sure you square the velocity first, then multiply it by mass and half it. Don't square the whole thing, which is a common mistake. What is gravitational potential energy and how do we calculate it? Gravitational potential energy is the stored energy in an object that can fall. In other words, it is up a height. And you get the gravitational potential energy by doing mass times by gravity times by height. Non-renewable energy, coal, oil, and natural gas, and nuclear are the four non-renewable energy resources. Non-renewable means once it's been used up, it can't be replaced. It will run out. Do not just say non-renewable means it's non-renewable. You won't get the mark. How do the four non-renewable energy resources work? And what are their advantages and disadvantages? So basically how a power station works, we use a fuel such as coal, oil, gas, or nuclear. We burn it to release heat. We boil the water into steam. The steam turns the turbine, and the turbine turns the generator. And then the generator generates the electricity. That's how you would get six marks if it was a six-mark question. Advantages, it's cost-effective, it produces large amounts of energy, it's easily available, the fuel is easily transported, it's reliable, and it's low running costs. The disadvantages is it's non-renewable, so the resources are running out. It has high setup costs to build a power station in the first place. It [snorts] releases carbon dioxide when burned. That's a good one to see. Which is the greenhouse effect and global warming. It also releases sulfur dioxide and nitrous oxides which cause
Segment 28: 32:30 - 35:00 acid rain. Cool mining can destroy landscapes. Oil spillages create environmental problems. So, that was all the advantages and disadvantages for coal, oil, and gas. Moving on to nuclear. Advantages is it produces large
Segment 29: 35:00 - 37:30 amounts of energy. Definitely say that. It's reliable. Once again, just like coal, oil, and gas, you can burn it anytime, day or night. Doesn't matter what the weather's doing, either. It's clean. So, it doesn't cause the CO2, SO2, and NO2 like coal, oil, and gas. Disadvantages, once again, just like coal, oil, and gas, it's non-renewable. It's going to run out. Um nuclear waste is a problem. It's very dangerous and it's difficult to dispose of. It's expensive to build a power station and final decommissioning, which means one day you're going to have to rip it down and get rid of it safely because the parts will be radioactive. And there is a risk of a major incident such as Chernobyl disaster in 1986. Renewable energy resources. Renewable means it can be replaced. So, it won't run out. Examples are solar, wind, geothermal, wave, hydroelectric, tidal, and bio mass. In other words, known as biofuel. They're all renewable energy resources. And make sure you've got a rough idea of how they work. Advantages and disadvantages of renewable energy resources. So, renewable energy resources release less carbon dioxide into the atmosphere, so cause less global warming. Make sure you always say that. It releases less sulfur dioxide and nitrous oxides in the atmosphere, so causes less acid rain. What is global warming? It's when carbon dioxide is released into the atmosphere, it causes global warming by trapping the sun's heat, which is what we call the greenhouse effect, and it's heating up the planet. What is acid rain? It's smoke containing sulfur dioxide and nitrous oxides are acidic. If they get into clouds, they cause acid rain, which affects plants, lakes, and buildings. Now, that doesn't come up quite so often anymore. Right, moving on to the next chapter, waves. A wave transfers energy without transferring any matter. All waves are either transverse waves, so
Segment 30: 35:00 - 37:30 they go up and down like that, or the longitudinal waves, which go backwards and forwards like that. Examples of transverse waves, so all of the seven electromagnetic waves, so radio, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays, they're all transverse. The water waves are transverse, and
Segment 31: 37:30 - 40:00 you've also got S waves, which are a type of seismic wave. Now, you only learn about those in the triple science, though. Examples of longitudinal waves are sound waves. It's the main one to go for. Again, there are waves called P waves, which are longitudinal, but uh they are triple only as well. So, just stick with saying sound waves for longitudinal. Words we use to describe waves. Wavelength, frequency, amplitude, period, wave speed. What do they mean? Well, the wavelength is the distance from a point on one wave to the same point on the next wave. So, the point on one wave to the same point on the next wave. You can pick any point you want. So, from there to there is the wavelength, from there to there or even from there to there, but that's making things difficult for yourself. Make sure you know that the top of a wave is called a peak and the bottom of the wave is called a trough. And this is a symbol called lambda, which we use to represent wavelength. Longitudinal waves, wavelength once again is from any point on the wave to the same repeating point on the next wave. Where the wave gets squashed is called a compression. Where the wave gets spread apart is called a rarefaction. Frequency is the number of waves passing a point each second. It's measured in hertz. So, in 1 second, if you've got three waves, that's 3 hertz. Six waves is 6 hertz. Nine waves in a second is 9 hertz. And you can see that as the frequency gets bigger, the wavelength gets smaller. Amplitude is the maximum displacement of a point on a wave away from its rest or undisturbed position. So, the undisturbed position, if water was flat, it would be undisturbed. Soon as it gets windy, you get a wave, you'll get amplitude. So, from the middle to the top is the amplitude. Also, from the middle to the bottom is amplitude. What amplitude is not is from the very top to the very bottom. That is twice the
Segment 32: 37:30 - 40:00 amplitude. If you've got a bigger amplitude, you've got more energy. And obviously smaller amplitude, less energy. How to describe a transverse wave. So, for two marks, you say the vibration of the particles are at 90° or perpendicular to the direction that
Segment 33: 40:00 - 42:30 the energy is traveling. So, the energy is traveling that way and the vibrations are up and down at 90°. How to describe a longitudinal wave. Vibration of the particles is in the same direction or parallel that the energy is traveling. So, the energy is traveling that way and the vibrations are going that way as well. So, that is parallel. Light and the electromagnetic spectrum chapter. So, the electromagnetic spectrum the seven waves to radio, microwave, infrared, ultraviolet, x-rays, and gamma. The way that you remember it is region martians invade Venus using x-ray guns. Radio, microwave, infrared, visible, ultraviolet, x-rays, and gamma. Now, they can put the spectrum anywhere they want. You've got the long waves on the right here and the short waves on the left, but it could be flipped. You need to know the uses and dangers of the electromagnetic spectrum. Now, these always come up, so pay attention. So, the uses gamma is used to treat cancer. X-rays is used to check bones and inside luggage. Sunbeds is used for ultraviolet. Cameras visible light. TV remote controls is your infrared and basically cooking. Cooking and communications microwaves and general communications radio. Now, what about the dangers? So, gamma causes cancer. X-rays also cause cancer. Ultraviolet causes skin cancer. Infrared cause burns. Microwaves heat body cells and cause burns. Radio waves are relatively safe unless they are in high concentration rate. Typical questions, which wave has got the shortest wavelength? Bosh. Gamma. Which has got a frequency between gamma and UV? That is x-rays. What can be seen by humans? Visible light. What's got the lowest frequency? So, remember the frequency is how many waves you've got per second. Over here, you've got not
Segment 34: 40:00 - 42:30 many waves per second. And then over here, you've got more waves per second. So, the lowest frequency was the radio over here, not many waves per second. What's got a wavelength just longer than
Segment 35: 42:30 - 45:00 infrared? So, there's infrared, and the wave is getting longer over here, so that's microwaves. What's got a frequency higher than x-rays? X-rays is here. Frequency is getting higher over there, so it's gamma. Invisible light, what's got the highest frequency? Now, that's going to be violet. So, visible light here, you have got Richard of York gave battle in vain. Red is always the longest wavelength, and violet is the shortest. So, red is next to infrared, and violet is next to ultraviolet. Radio waves are higher only. So, the question could be for six marks, explain how radio waves are made and detected. Now, this is tricky. This is how you get your six marks. Radio waves are produced by oscillations, so alternating current in electrical circuits. A metal rod or wire can then be used as an aerial because it absorbs the radio waves and causes oscillations in the circuit connected to the aerial. So, in other words, you get alternating you get alternating current coming in to this aerial here, and it creates radio waves of the same frequency. Now, those radio waves come over onto this aerial, and the radio waves create an alternating current. So, alternating current went into this aerial, created radio waves, and those radio waves create alternating current in this aerial. That's basically it. Reflection and refraction. Waves will travel in a straight line unless they are reflected or refracted. Reflection is when a wave bounces off a surface. Reflection is bending of a wave when it enters a different density medium causing a change in velocity. And again, this is higher only. So, reflection or refraction off the ionosphere. So, you need to know the ionosphere is an upper layer in the atmosphere with charged particles, hence
Segment 36: 42:30 - 45:00 the word ion. >> [gasps] >> Radio waves longer wavelength can be refracted enough by the ionosphere and actually sent back to Earth communicating longer distance than just line of sight. So, there is a maximum range for microwave communications because the curved surface of the Earth gets in the way. So, microwaves and short radio waves can only travel so far cuz then they just get lost out in the space. So, what we do is we basically bounce
Segment 37: 45:00 - 47:30 the radio waves off the ionosphere or refract them down and then they can actually travel further. Microwaves are not refracted by the ionosphere cuz they've got a shorter wavelength. So, they can be used to communicate with satellites out in space. Bounce them up. Bounce them back. Radioactivity chapter, the model of the atom. So, J. J. Thomson's plum pudding model basically had positively charged material generally everywhere and you have little negative charged electrons scattered throughout in localized little positions. Then Rutherford came along with his gold leaf experiment, also known as the alpha scattering experiment, and you might have to explain how he did the experiment and what results he found. So, Rutherford fired positive alpha particles at a thin gold leaf, which is basically a piece of gold foil. So, that's what he did. So, these are the radioactive source of the alpha particles. This is the thin gold foil. He basically fired the positive alpha particles at the gold foil to see what's going to happen. Now, the first thing that he saw is that most alpha particles went straight through the foil for one mark. Some alpha particles were deflected by small angles. It's like you're taking a free kick a football and it hits the wall, gets deflected off the wall. And the third mark is very few alpha particles were scattered through large angles. And only one in about 6,000 actually bounced back off the gold foil. Now, for six marks, you might have to explain how the results are evidence that Rutherford discovered the nucleus. This is what you see. So, you've got your positively charged nucleus. So, this is like the gold foil dangling down here.
Segment 38: 45:00 - 47:30 And the electrons were in the space around the nucleus. So, he took the tiny positive alpha particles, fired at the gold sheet. Now, as I've just said, most alpha particles passed straight through. Now, what does that mean? It proves that most of an atom is empty space. Now, some alpha particles got deflected by a small amount. What does that mean?
Segment 39: 47:30 - 50:00 Well, it proves that the nucleus is positive cuz he knew that the alpha particles were positive, so they would only get deflected if they came next to something else that was also positive. So, that's for your third and fourth marks. And for your fifth and sixth marks, very few alpha particles bounced back after hitting the dense mass of the nucleus, proving the nucleus must be very small compared to the size of the atom. So, that is how you get your six marks. How big is the atom? So, the radius of a nucleus is about 1 * 10 to the minus 15 m. The radius of an atom is about 1 * 10 to the minus 10 m. Just in case they are multiple choice questions. Make sure you know those numbers. The atom is 100,000 times bigger than the nucleus. That is five zeros. So, the difference is five zeros. Right, the structure of an atom. So, you've got your electron on the outside in the shells. You've got your protons and your neutrons in the nucleus in the middle. Inside atoms, typical questions. So, you'll need to know what the subatomic particles are, where you find them, what their charges are, and what the masses are. So, protons in the nucleus. Pa pa pa proton, pa pa pa positive charge. Mass of one. Neutron in the nucleus. Charge zero, neutral neutron. Relative mass one. Subatomic particle found around in the shells, electron. Charge minus one. Relative mass one divided by 1,835. That's a negligible mass. Just like in chemistry, as a guide to subatomic particles, this top number here is your mass number. That is the number of protons added to the number of neutrons. This bottom number is the proton number. Remember, the proton number is the same as how many electrons you've got because all atoms are electrically neutral since they have the same number of positive and negative charges. So, the same
Segment 40: 47:30 - 50:00 number of protons and electrons. The neutrons, you need to subtract the atomic number from the mass number and you'll end up with the number of neutrons. Again, very common questions. Isotopes, they've got the same number of protons for one mark, but a different number of neutrons for another mark. Sometimes you can see it's the same atomic number but they're different mass number. So, for example, carbon 12, because it's
Segment 41: 50:00 - 52:30 carbon, it's always got the same number of protons, 6 6 6, but it's got a different number of neutrons. That one's got six, that one's got seven, that one's got eight. Eight and six is 14, seven and six is 13, six and six is 12. So, these are the mass numbers. Electrons and orbits. Emission spectrum and absorption spectrum. That is the evidence that electrons orbit the nucleus in shells. Atoms can absorb energy. This creates an absorption spectrum like this one here, and atoms can re-emit the same energy, and this creates an emission spectrum like here. So, that energy there is the same as that energy there. That's the energy getting absorbed. That's why there's no color at that particular point of the spectrum, and it's being re-emitted. That's why there is a color in this spectrum. Explain how Bohr, Niels Bohr, discovered electron shells for six marks. So, we've got neon here, electron configuration 2 8. So, two electrons in the first shell, eight in the second shell. And these shells will usually be empty. Now, Bohr discovered if an atom absorbs energy, the electron can move into a higher orbit, and that'll create a line on the absorption spectrum. He also discovered when the electron returns to its lower shell, the atom emits energy as visible light in a particular wavelength that creates a line on the emission spectrum. Six marks. So, ionization. Sometimes an atom gains so much energy that one or more of the electrons can escape from the atom altogether. An atom that has lost or gained electrons is called an ion. Radiation that causes electrons to escape is called ionizing radiation. Background radiation, background radiation is radiation that we are constantly being exposed to at low levels from space and radioactive substances in the environment. Sources
Segment 42: 50:00 - 52:30 of background radiation pie chart, all sources are natural except the following which are man-made, medical from hospitals, so x-rays and treating cancer, and nuclear and other. So, from nuclear power station leaks and nuclear bombs.
Segment 43: 52:30 - 55:00 And the pie chart always adds up to 100%, so if something is missing, you can work out what that value must be. Types of radiation, so alpha particles contain two protons and two neutrons. So, it's just like the nucleus of a helium atom, but do not have any electrons. So, make sure you know that, four two, mass of four, charge of two. There we go, four particles. Beta particles are high-energy, high-speed electrons, but are from the nucleus, not from the shells. So, if they're electrons, they've got the same mass as the electron, and they've got the same charge as the electron. So, the symbol is zero mass charge of minus one, or you could say it written like that. Gamma rays are high-frequency electromagnetic waves. They've got no mass, they've got no charge, they are waves, not particles. So, no mass, no charge. And the symbol looks like that. Other types of radiation, you've got positrons, which is high-energy, high-speed particles with the same mass as the electrons, but a charge of plus one. So, no mass, charge of plus one. Neutrons can also be emitted from an unstable nucleus. Relative mass of one and no electric charge. Relative mass of one and zero electric charge. Ionizing radiation, so alpha, beta, and gamma only. Radiation that can cause charged particles, ions, to be formed. It can cause tissue damage and DNA mutations. So, damages tissue, causes cancer. You'll need to know about the penetrating properties of alpha, beta, and gamma. So, alpha gets stopped by paper. Beta goes through paper but gets stopped by aluminum. And gamma only gets stopped by thick lead or really thick concrete. Six-mark question. Compare and contrast the different types of radiation, including their ability to ionize and penetrate. So, alpha, beta, and gamma only. So, here we go. The symbols, make
Segment 44: 52:30 - 55:00 sure you know those. What they are. So, alpha is two protons and two neutrons. Beta is high-energy, high-speed electron. Gamma is just a wave, high-frequency. Ionizing effect. Alpha, very ionizing. Beta, mid-ionizing.
Segment 45: 55:00 - 57:30 And gamma, weakly ionizing. How far it travels. Only a few centimeters for alpha, a few meters for beta, and a few kilometers for gamma. Now, they actually tie in. Because it's weakly ionizing, it travels very far. And because this is very ionizing, it only travels a few centimeters before it kind of runs out of energy. What's it stopped by? Paper is alpha. Beta gets stopped by aluminum. Gamma is stopped by thick lead, as I've just said. Radioactive decay. This is when a radioactive isotope emits ionizing radiation. Example, alpha, beta, or gamma. So, nuclear equations show what happens during the radioactive decay, and the rules are the total mass numbers and charge numbers at the start must equal the charge numbers and mass numbers at the end. The mass number's the top number, the charge number's the bottom number. So, you can see 226 went in. So, 222 + 4 = 226. And the charge number 88 went in. So, 2 + 86, that is 88 came out. So, make sure the numbers are balanced. Typical exam questions, describe what happens when a nucleus decays. State the effect of the decay on the atomic number and mass number of the nucleus that's decaying, and balance the nuclear equation. Okay. Sometimes when an unstable nucleus decays, it emits an alpha particle. So, that's two protons and two neutrons. State what this will do to the mass number of the nucleus. Well, it'll decrease by four. So, remember alpha is four little particles, two protons, two neutrons. If they're leaving the original nucleus, then the original nucleus decreases by a mass of four. State what this will do to the atomic number. Well, that'll decrease by two because two protons are leaving. Balance the nuclear equation. Okay, so you must know that alpha is 4 2, otherwise you won't be able to balance
Segment 46: 55:00 - 57:30 it. So, the mass that goes in has to equal the mass that comes out. And the charge that goes in has to equal the charge that comes out. So, that number must be 234, and that number must be 90. Beta decay. So, what happens during beta decay? A neutron changes into a proton and an electron, which is ejected from the nucleus. So, make sure you remember that. That's tricky. Neutron turns into a proton plus
Segment 47: 57:30 - 60:00 the beta. State what this will do to the mass number. Well, the mass number's going to stay the same cuz beta has got no mass. State what's going to happen to the atomic number. Now, it's actually going to increase by one. I'll show you what I mean. So, if you've got this thing, it kicks out a beta particle. These numbers here all have to add up. So, that must be 131 + 0 gives 131 that came in. And if that's -1, then that has to be 54. Cuz 54 + -1 = the 53 that went in. So, that confuses people. But, just make sure the numbers are balanced is the key to the kingdom. And obviously, make sure that you know that the beta is 0 -1. They don't often give you it. Gamma decay. A radioactive isotope may lose energy as gamma radiation when the nucleus is rearranged. This helps to make the nucleus more stable. So, just say a nucleus kicks out alpha and it's still got an excess of energy, it'll just kick out a gamma as well. So, the gamma usually comes out like after the alpha or the beta's given off. State why emitting gamma radiation does not change the atomic number or mass number. Well, gamma is a wave, not a particle. So, it's got no mass and it's got no charge. Balance the nuclear equation. Well, if that's 0 0, this thing here is just basically going to have exactly the same numbers as this thing here. Except this was excited cuz it had extra energy. Now, that one's going to be more stable. Beta plus a positron decay. During positron decay, a proton becomes a neutron and a positron. A proton becomes a positron if that helps. State what this will do to the mass number of the nucleus. So, remember a positron is 0 and +1.
Segment 48: 57:30 - 60:00 So, it's going to stay the same. The mass doesn't change cuz the mass of the positron's negligible. Atomic number, that's going to decrease by one. Cuz remember, a proton is going to turn into a neutron. So, if it was a proton number of 10, now it's going to go down to nine. The mass isn't going to change, cuz a proton, mass of one, charge of one, is going to turn into a neutron, mass of one, charge of zero, plus it's going to give out the positron. And once again, you can see that the numbers all add up on the top, and the
Segment 49: 60:00 - 62:30 numbers all add up on the bottom. Sometimes they do actually ask you about that. Balance the nuclear equation, not required. I have seen it sneak in mind. And if you do learn that, it will help you to remember what's going on up there. Neutron decay. Sometimes when an unstable nucleus decays, it emits a neutron. State what this will do to the mass number of the nucleus. So, a neutron, mass of one, charge of nothing. So, if it's kicking out a neutron, the mass is going to decrease by one. What's it going to do to the atomic number? Nothing, cuz that number there is nothing. It's not kicking out any protons. Balance the nuclear equation, again, not required. Half-life. Radioactive decay is a random process. We cannot predict when it's going to happen. However, we can use a half-life because it allows us to predict the activity of a large number of nuclei. What is a half-life? The half-life of an isotope is the time it takes for the activity to half. That's my personal favorite definition of it. Another definition is the half-life is the time it takes for half of the unstable nuclei in a sample of radioactive isotope to decay. Bit waffly that one. The half-life is the same for any mass of a particular isotope. So, it doesn't matter how much of the isotope you've got, if you've got 10 kg or if you've only got 5 kg, the half-life will still be the same. If that was 30 days for the half-life, then this will also be 30 days. Don't think the half-life halves just because the amount of mass of it you've got have halved. That's often a trick question. Half-life graph. So, you can see at the start we've got 16 unstable nucleus or nuclei. And then a short time later, a one half-life later, you've only got eight
Segment 50: 60:00 - 62:30 left. So, eight unstable and eight decayed nucleus that's more stable. So, for example, this one here must have kicked out perhaps an alpha particle. And now it's become stable. Another half-life later, you'll only have four unstable nuclei, then two, then one. Now, using the half-life graph to calculate half-life. So, choose a starting point. Now, we usually go from when the time is zero. Read what the activity is at that time. So, for example, time of zero, the activity was
Segment 51: 62:30 - 65:00 10,000 becquerels. Make sure you know the units for activity. You can get a mark for that. Then use the graph to see how long it takes the activity to half. So, what's half of 10,000? 5,000. Okay. Draw your little line going across from 5,000 to the graph and then drop your little line onto the axis for time. And that'll basically tell you what the half-life is. So, in this case, it's 30 years. Make sure you pay attention to what the units are. Sometimes it's years, sometimes it's minutes, sometimes it can be seconds. So, let's make sure you've understood that. Work out the half-lives of the two sources shown above. So, source A, the blue one. So, see what the activity is at time zero. So, it's 120. Now, what's half of 120? 60. So, draw your little dotty lines. The examiners love that. Little dotty lines come down here. So, the half-life of source A is 5 seconds. Now, let's do the same for source B. So, once again, source B, at time of zero, the activity was 120. What's half of 120? Well, 60. So, draw your little dotty lines again until you hit the graph and then come down onto the x-axis. That's 20 seconds. So, the half-life of B was 20 seconds. Common question. Now, what's the half-life always stays the same. So, what's half of 60? 30. So, if we actually drew little dotty lines going across to the graph, you can see it's halved again in 20 seconds. So, the half-life for a particular substance is always the same, regardless of how much mass of the substance you've got. Practice questions. Strontium 90 has a half-life of 29 years. How many strontium 90 half-lives is 29 years? Well, that's one half-life. What about 58 years? Well, how many times does 29 years fit in there? 58 years? Two. So, that's two half-lives.
Segment 52: 62:30 - 65:00 There are 10 million atoms in a sample of radon 222. It has a half-life of 4 days. How many undecayed nuclei are left after 4 days? Well, that's one half-life has passed, so you're going to have half of 10 million. You're going to have 5 million. How many will be 8 days? Well, 8 days is two half-lives, so it's going to half and half. So, you're only going to have 2.5 million. And what about 12 days? Well, that's going to be 4 days plus 4 days
Segment 53: 65:00 - 67:30 plus 4 days. That's your 12 days. So, it's going to half and half and half. So, if you started with 10 million, it's going to half to 5 million, Then it's going to half to 2 and 1/2 million. Then it's going to half to 1.25 million. So, three half-lives. Dangers of radioactivity or radiation. That's when someone is exposed to radiation from nearby sources. Irradiation stops when they move away from the source. >> [sighs] >> Contamination is worse. That's when the particles of radioactive material get on someone's skin or inside their body. For example, if they breathe in a radioactive gas. As the material decays, they will continue to be exposed to the radiation until it's all decayed or is removed. Radiation in hospitals, medical staff working with radioactive sources have their exposure limited in several ways. So, how can you reduce being exposed? You can increase your distance from the source. In other words, handle it with tongs. Never pick it up with your fingers. Shielding from the source or wear a lead-lined apron and limit the e-time spent near the radioactive source. Exposure can be closely monitored using a dosimeter badge. Basically, the badge there'd be a little bit of photographic film in here. And that photographic film turns from clear to dark the more radiation they are exposed to. So, as this gets darker and darker and darker, it means you're being exposed to more radiation. And that is the end of the video. So, if you made it to the end, that's an OB guarantee that your grade is going to go up. Very best of luck in your exams. And as always, work hard and be nice. Want to see more videos like this? Subscribe
Segment 54: 65:00 - 67:30 to my channel, GCSE Physics Explained. >> Mhm.