All of OCR PHYSICS Paper 1 in 40 minutes - GCSE Science Revision (Gateway)

Summary

Highlights

• Learn about the plum pudding model and how atomic theory evolved! 🍮
• Discover how isotopes differ due to neutrons! ⚛️
• Understand the difference between solid, liquid, and gas states of matter! 💧
• Dive into forces, vectors, and Newton's laws of motion! 🎯
• Explore circuits, Ohm’s law, and electrical components! 🔋

Key Takeaways

• Atomic structure includes protons, neutrons, and electrons! 🧪
• Density is mass per unit volume—different materials, different densities! ⚖️
• Forces can be contact or non-contact, like magnetism or gravity! ✔️
• Electricity is all about the flow of charge through circuits! 💡
• Magnetism involves magical invisible fields that attract and repel! 🧲

Overview

Chapters

• 00:00 - 00:30: Introduction and Overview The 'Introduction and Overview' chapter provides a quick overview of what students need to know for the OCR GCC Physics Paper 1, applicable to Foundation Tier, Double Combined, and Triple or Separate Physics. It covers topics such as matter, forces, electricity, and magnetism. The guidance clarifies which parts are for Triple Physics only, while noting that the difference with the higher tier is minimal. The chapter encourages students to pause and review when needed, to fully understand each concept.
• 00:30 - 01:00: History of Atomic Theory The concept of atomic structure evolved gradually over time. Initially, JJ Thompson introduced the plum pudding model, depicting the atom as a mixture of positive and negative charges. Later, Ernest Rutherford discovered the small, dense positively charged nucleus, proposing that electrons orbit far away from it. Further advancements came from Niels Bohr, who suggested that electrons exist in specific orbitals or shells, and James Chadwick, who identified the presence of neutral charges (neutrons) within the nucleus.
• 01:00 - 01:30: Atomic Structure and Isotopes The chapter explains that atoms consist of neutrons (neutral charge) and protons (positive charge). Each type of atom is represented by a symbol on the periodic table, and each element is defined by an atomic number, which is the number of protons in its nucleus. The mass number, consisting of both protons and neutrons, helps in identifying different isotopes of the same element, such as carbon having isotope variations with six or seven neutrons.
• 01:30 - 02:00: Density and Measurement Techniques In this chapter titled 'Density and Measurement Techniques', the concept of isotopes is introduced as atoms of the same element but with different neutron numbers. The text explains that density indicates how compact the mass is within a material or object, using the example of comparing iron and cream to highlight that iron has a higher density. It further clarifies that density is not measured in kilograms per cup but in kilograms per cubic meter, with the formula being density equals mass divided by volume. The symbol for density is the Greek letter rho (ρ), described as a 'p' without the ear. The discussion suggests that density depends on the particles that compose the material.
• 02:00 - 03:00: States of Matter and Changes in State This chapter explores the states of matter, focusing on the differences between water in its liquid and gas forms, namely water vapor and liquid water. It discusses how water vapor is less dense than liquid water because the molecules are more spread out in gas form. Additionally, the chapter explains how to calculate the density of regular objects by determining their dimensions and using a balance to obtain their mass, and then applying the appropriate equation.
• 03:00 - 04:00: Specific Heat Capacity and Thermal Energy This chapter discusses the limitations of using a ruler for measuring small dimensions and suggests using vernier calipers and micrometers for more accurate measurements. Vernier calipers have a resolution of 0.1 mm while micrometers can measure down to 0.01 mm, making them suitable for very thin objects like wires. The chapter also touches on the concept of using displacement methods to determine the volume of irregular objects, using a chess piece as an example.
• 04:00 - 05:00: Internal Energy and Changes of State The chapter begins with a reference to the famous 'Eureka' moment of Archimedes, relating to the displacement of water, which is introduced as a method for measuring volume. By submerging an object in water and measuring the displaced volume, the volume of the solid object can be determined. Solid, liquid, and gas are discussed as the three main states of matter, using water as an example that can exist as ice (solid), where particles vibrate, or in other states.
• 05:00 - 07:00: Gas Laws and Pressure The chapter discusses the different states of matter: solid, liquid, and gas, focusing on the properties that distinguish them. Solids have fixed positions, while liquids, like water, have molecules that are still touching but can move past each other. In gases, such as water vapor, particles are far apart and move randomly, allowing gases to be compressed, unlike solids and liquids. The transition from solid to liquid (melting) or liquid to gas (evaporation) requires energy, typically in the form of heat, to overcome the electrostatic forces between particles. The concept of specific heat capacity is introduced, where it can be determined by heating a material and measuring the change in its temperature, exemplified by using an electric heater.
• 07:00 - 10:00: Forces and Newton's Laws The chapter discusses the process of measuring the specific heat capacity of different metals. It involves using a heater, voltmeter, ammeter, balance, timer, and thermometer. The process includes measuring the potential difference (PD) and the current to calculate power, which is then multiplied by time to find the energy input. This data is used in a rearranged specific heat capacity (shc) equation to find results.
• 10:00 - 12:00: Momentum and Collisions This chapter discusses the concept of energy transfer during the heating process, noting that some energy is lost to the surroundings, impacting temperature change measurements. It explains the process of heating ice, describing how temperature increases until it reaches the melting point, where it remains constant until completely melted.
• 12:00 - 21:00: Electricity Basics and Circuit Components This chapter provides an overview of the basic principles of electricity and the components of circuits. It explains the concept of internal energy in substances, which is the sum of their kinetic and potential energies. It highlights that during a change of state, particles do not gain kinetic energy but potential energy, and only one of these energy types can change at a time: an increase in temperature results in increased kinetic energy, while a change in state involves a change in potential energy.
• 21:00 - 25:00: Magnetism and Electromagnetism This chapter explores the concepts of magnetism and electromagnetism. It points out how heating relates to an increase in potential energy and discusses equations related to energy changes. Initially, the equation for the increase in thermal energy is presented as E = mcΔT, where 'm' is mass, 'c' is specific heat capacity, and 'ΔT' is the change in temperature. It explains that this formula applies to an increase in the kinetic energy of particles during a temperature change. During a phase change, however, temperature remains constant, making the specific heat capacity equation inapplicable. Instead, the chapter introduces the concept of specific latent heat (SLH) as a more relevant measure, describing how SLH indicates the heat absorbed or released during a state change without temperature variation.
• 25:00 - 29:00: The Motor and Generator Effect This chapter discusses the energy required to change the state of 1 kilogram of a substance, such as the specific latent heat of fusion for water, which is 334,000 Joules per kilogram. The energy equation is E = mL, where E is energy, m is mass in kilograms, and L is specific latent heat in Joules per kilogram. The chapter also touches on the behavior of gases, noting that gas particles are spaced far apart, move quickly, and randomly, and gain kinetic energy when heated.
• 29:00 - 38:00: Transformers and the National Grid The chapter discusses the behavior of gases in a closed container, explaining how increasing the speed of gas particles raises the pressure exerted on the container walls due to more frequent and forceful collisions. It also covers the relationship between pressure and volume at constant temperature, where the product of pressure and volume remains constant, indicating that if one increases, the other must decrease. Additionally, the concept of compressing a gas is introduced, which involves exerting an inward force, essentially doing work on the gas, to increase its pressure.
• 38:00 - 39:00: Conclusion and Final Tips The chapter discusses the concept of inverse proportionality between pressure (P) and volume (V), highlighting that if one doubles, the other halves. It introduces the formula P1V1 = P2V2, representing the relationship before and after a change in conditions. Volume is measured in cubic meters (m³), while pressure is measured in Pascals (Pa), equivalent to Newtons per square meter. The chapter explains that higher altitudes lead to a less dense atmosphere due to fewer particles in a given volume, resulting in lower pressure. It concludes with an explanation of pressure as a measure of force concentration.

All of OCR PHYSICS Paper 1 in 40 minutes - GCSE Science Revision (Gateway) Transcription

• 00:00 - 00:30 let's see how quickly we can cover everything you need to know for OCR GCC physics paper 1 this is good for high round Foundation Tier double combined and triple that is separate physics so papers 3 five or 72 see I'll make it very confusing it's just the first physics paper you do and it includes matter forces electricity and magnetism I'll tell you when something is just for triple but not when something is just for higher tier as there's not a lot of difference to be honest we're going to be gunning it so pause the video if you need a bit more time to get your head around something you see let's go ni
• 00:30 - 01:00 remember this first bit from chemistry paper one the idea of what atoms are like came about gradually JJ Thompson discovered that atoms are made up of positive and negative charges he came up with the plum pudding model of the atom a positive charge with lots of little electrons dotted around it it was Ernest Rutherford who found out that the positive part of the atom must be incredibly small We Now call this the nucleus and the electrons must orbit relatively far away from it Neil's ball later discovered that electrons exist in shells or orbitals then James Chadwick discovered that the nucleus must also contain some neutral charges he called
• 01:00 - 01:30 them neutrons while the positive charges are called protons different types of atoms are represented by symbols which we also find in the periodic table the bottom number is the atomic number that's the number of protons in the nucleus this is what determines what element you actually have the top number is the mass number this tells you how many protons and neutrons are in the nucleus so that must mean that this carbon atom has six neutrons on top of it six protons to make 12 however you can get a carbon atom with seven neutrons instead so its mass is 13 these
• 01:30 - 02:00 are isotopes atoms of the same element but different numbers of neutrons density tells you how compact mass is for a material or object for example a cup of iron has a much higher mass than a cup of cream showing that iron has a higher density but we don't measure density in kilog per cup but kilog per meter cubed so the equation is this density is equal to mass divid volume the symbol we use for density is the Greek letter row it's just a p without the ear on it density is depend dependent on what particles make up the
• 02:00 - 02:30 object and also how tightly packed together they are we know water vapor is less dense than liquid water because even though both made from water molecules they're more spread out when a gas so there are fewer of them in every M cubed finding the density of a regular object that is an object with a volume that can be calculated using its Dimensions is easy for example the volume of a cuboid a rectangular object can be calculated by multiplying the length of its three sides then we just pop it on a balance to get its mass and then use the equation to find the
• 02:30 - 03:00 density for Dimensions that are a few millimeters in length a ruler won't be that accurate as its resolution will likely just be 1 mm so you could use verer calipers instead they usually have a resolution of 0.1 mm a tenth of a millimeter objects that are very very thin like wires need a micrometer instead they usually have a resolution of 0.01 mm or 100th of a millim the volume of an irregular object like a chest piece for example cannot be calculated from measurements instead we use a displacement C can also called a
• 03:00 - 03:30 Eureka can after the Greek philosopher Archimedes got into a bath fall to the brim displacing the same volume of water as his volume tie thin string around the object and gently lower it until it's just under the water line and wait for the water to stop dripping out into the beaker that you hopefully put there beforehand we decant this water collected into a measuring cylinder to get the volume of water displaced and therefore the volume of the object solid liquid and gas are the three main states of matter for example water can be ice a solid where particles vibrate around
• 03:30 - 04:00 fixed positions it can also be water where the molecules are still touching but free to move past each other and gas water vapor where the particles are far apart and moving randomly which is why it can be compressed while solids and liquids cannot to melt a solid or evaporate a liquid you must supply energy usually in the form of heat to overcome the electrostatic forces of attraction between the particles we can find the specific heat capacity of a material by heating it up and measuring the change in its temperature for example we can use an electric heater
• 04:00 - 04:30 that slots into cylinders made of different Metals we turn the heater on use a voltmeter to measure the PD and Amer to measure the current and we multiply these to get power more on this later by the way we use a balance to measure the mass of the block we use a timer and a thermometer to measure how much the temperature of the block has increased by in a certain time say 60 seconds we take the power and we multiply it by the time to get the energy that's gone into the block and then we pop these numbers into our re rearranged shc equation the issue is
• 04:30 - 05:00 that while heating some energy will be transferred to the surroundings which means that the temperature change that we measure will be less than what it should be so invariably our final value for the sh will be higher than the True Value if you have a block of ice and Supply heat to it its temperature will increase the particles vibrate faster which means they're gaining kinetic energy however once it reaches the melting point of 0° C its temperature will remain constant until it's all melted only then will its temperature start increasing again the same thing
• 05:00 - 05:30 happens when it reaches 100° and it turns into a gas but why the constant temperature after all energy is still going into the ice but during a change of state the particles don't gain kinetic energy but rather potential energy we say that any substance has internal energy that's the sum of the kinetic energy and potential energy of all particles in a substance you need to know this definition only one of these can change at a time an increase in temperature means we must have an increase in kinetic energy of the particles while a change in state when
• 05:30 - 06:00 heating anyway must mean an increase in potential energy we have equations for both of these energy changes we saw at the start the equation for increase in thermal energy which was eal MC delta T mass time shc time change in temperature we now know that this is only for an increase in kinetic energy of particles in a substance when there's a change in temperature during a change of state the temperature stays constant so we can't use the specific heat capacity equation instead we use the slh equation specific lent heat slh of a substance tells you
• 06:00 - 06:30 how much energy is needed to change the state of 1 kilogram of it for example the slh of fusion that just means melting or freezing for water to ice is 334,000 Jew per kilogram that means the equation for energy needed to change state is this e equal ml energy equals mass in kilog times specific latent heat in Jewels per kilogram we know gases consist of particles that are far apart moving fast and randomly if you heat the gas the particles gain connect I energy
• 06:30 - 07:00 and they move faster this means that they collide with the walls of the container the gases in with a greater force and more frequently which results in an increased pressure pushing outwards you also need to know that you can also increase the pressure by compressing a gas to do this you need to exert a force inwards on the gas we also say that this is doing work on the gas you also need to know what happens if a gas is at a constant temperature in this case pressure times volume is equal to a constant that means that if P or V goes up the other one goes down that means p
• 07:00 - 07:30 and v are inversely proportional one doubles the other one halves we can therefore say that P1 V1 that's the pressure and volume before the change is equal to p2v2 afterwards we know volume is measured in me cubed but pressure is measured in Newtons per met squared but we also call this pascals PA for short the higher your altitude the less dense the atmosphere becomes due to there being fewer particles in any given volume hence pressure also decreases you can think of pressure as being how concentrated a force is the equation is
• 07:30 - 08:00 pressure is equal to force divided by area so the unit for pressure is Newtons per met squar but we can also call this unit pascals or PA for short you probably know the deeper you go underwater the greater the pressure and this is due to the weight of the water above your head pushing down on you we can calculate this pressure using p equal H row that's just a Greek letter time g h being height of the water column above you basically depth times density time gravitational field strength the density of water is 1,00 kg
• 08:00 - 08:30 per Meer cubed a force is any push or pull forces can be contact forces that's when objects are physically touching like when you push a door or they can be non- contct like magnetism electrostatic forces and gravity This Is A New Concept in gcsec physics and shocker it's a silly one because even contact forces are due to the electrostatic repulsion between electrons in your skin and the door for example but whatever technically pushing a door involves a normal contact force while other contact forces could be friction a resistance and tension the important thing is that
• 08:30 - 09:00 we can represent forces with vectors that is an arrow that shows the direction and magnitude of the force the magnitude is the size of the force and that's indicated by the length of the arrow if two forces act on an object there's a resultant Force we find this by technically adding the vectors however if they're going in opposite directions one must be negative so in this case the resultant force would be 3 Newtons to the right and that's positive if we've decided that positive is in the right direction if vectors are at right
• 09:00 - 09:30 angles to each other you use Pythagoras to find the resultant this works because you can make a triangle by moving one of the forces you could also be expected to use trig that's socker TOA to find either one of these angles chanes is going to be tan you use if any if forces are balance that is they add up to zero that means that the object will not accelerate it won't change velocity no that doesn't necessarily mean it's not moving it just stays at a constant velocity and that could be 0 m/ second of course this is Newton first law of
• 09:30 - 10:00 motion by the way more on those in a bit if a measurement or quantity just has magnitude but no direction it's not a vector but it's called a scalar instead here are some examples of both note that displacement is distance traveled with a direction while similarly velocity is the vector form of speed weight is another name for the force due to gravity that acts on an object it's calculated by multiplying the mass in kilogram by gravitational field strength or G which here on Earth is 9.8 Newtons per kilogram sometimes we just round up to 10 you'll be told which to use in a
• 10:00 - 10:30 question that means that 1 kg of Mass on Earth has a weight of 10 Newtons now if you hold an object up with your hand you must be pushing up with a force that is equal to its weight in order for the forces to be balanced and so it doesn't accelerate however that means that if you lift it upwards at a constant speed that's also true that's something that people often forget to lift something at a constant speed you must be lifting with a force that's the same as the weight we can therefore then calculate the energy that is used to lift this object object using the equation for
• 10:30 - 11:00 work done that's work done equals force time distance moved work done is just a fancy term for energy transferred by a force this equation is true for any situation but in this case the force is the weight and the distance is the height so we could say the gain in energy is equal to mass * G * H does that look familiar it should because that's the exact same equation for calculating gravitational potential energy that's GP gained to be precise forces can also deform an object if you
• 11:00 - 11:30 pull on a spring that is fixed at one end it will stretch or extend hooks law states that F equal ke that's Force equals spring constant sometimes called stiffness times extension the unit for spring constant is Newtons per meter this works for any object that stretches elastically that is returns to its original shape once the force is removed it can also be true if an object is compressed instead we can see that as K is a constant force and extension are directly proportional that means what whatever happens to one happens to the
• 11:30 - 12:00 other double the force double the extension you can hang varying masses off a spring and measure the extension and you'll end up with a straight line that goes through the origin 0 0 and that proves this directly proportional relationship if you carry out this experiment just make sure your ruler zero Mark is lined up with the bottom of the spring that way you can be sure you're only measuring extension rather than the length of the whole spring that would introduce a systematic error if you did that by mistake also make sure you're at ey level with the bottom of the spring when measuring against the
• 12:00 - 12:30 ruler to avoid Parallax error and that is a random error rather than a systematic error the energy stored in the spring is equal to half k^ squ something was attached to the spring and you let go the object would gain the same amount of kinetic energy at least in an ideal or closed system that is no energy is loss of the surroundings due to heat for example just for Triple A Moment is a turning Force for example what you do with a spanner this is equal to force time distance to the pivot so the just ends up being newton meters
• 12:30 - 13:00 note that this looks similar to the work done equation but this force and distance here are perpendicular to each other rather than parallel similarly to just normal forces if the moments turning clockwise are equal or balanced with the moments turning anticlockwise the object will not turn that is if it wasn't turning to begin with we can call this the principle of Moments by the way an application of moments is Gears a small gear can turn a large gear in order to increase the moment produced back to double speed and velocity are measured in me/ second while velocity
• 13:00 - 13:30 also has Direction so it could be positive or negative or up and down left and right here is some typical speeds for when you're traveling of course speed and velocity are calculated by distance or displacement over time if you have a distance time graph the gradient of the graph gives you the speed or velocity if it's a curve just draw a tangent at the point you need to and find its gradient a speed or velocity time graph can give you even more information this time the gradient gives you change in speed divided by time which is acceleration ation here's
• 13:30 - 14:00 the equation two the unit of acceleration is m/s squared and it tells you how quickly speed is changing if it's a negative gradient heading to zero that means the object is decelerating slowing down however this graph can also go into negative values for example when a ball is thrown upward and comes back down in that case the velocity starts positive and fast but decreases to zero when it reaches the top where it then turns around so the velocity becomes more negative as it falls incidentally this Gra has a constant negative
• 14:00 - 14:30 gradient gravity is accelerating it downwards at a constant rate even though its direction changes what you find is that for any object that's falling its acceleration is 9.8 m/s squared the same as gravitational field strength because they are the same thing a velocity time graph can also give you the distance traveled you get that by calculating the area under the graph any area under 0 m/s counts as negative displacement by the way thus where the area of both these triangles and this graph adds up
• 14:30 - 15:00 to zero that makes sense though doesn't it seeing that it's gone back from whence it came I.E your hand suat or Newton's equations of motion are a way of predicting what an object will do if it's accelerating s is displacement U is initial velocity V is final velocity a is acceleration and T is time U is zero if it starts at rest V equals z if an object is moving to begin with but then decelerates to a standstill for objects falling a is the same as G that's 9.8 m/ second squ for any question involving
• 15:00 - 15:30 one of these equations you write down your variables put a question mark next to what you're trying to find and put the values next to the other three that you've been given you can ignore the fifth unused variable depending on what data you're given you pick the correct equation with the four variables in rearrange it if necessary then just plug in your numbers we already know that Newton's first law is this when there's no resultant Force an object's motion is constant in other words no change in velocity that could be because there's no forces acting or the forces are balanced by the way inertia is the term
• 15:30 - 16:00 we use to describe the tendency for an object's motion to stay constant unless acted on by a resultant Force Newton's Second Law involves unbalanced forces that is there is a resultant Force this is equal to ma masstimes acceleration that's all Newton's second law is f equals ma only one of these can be true in any situation there's either no resultant force or there is we can prove Newton's second law by doing a PR iCal we use a trolley on a track being pulled
• 16:00 - 16:30 by the weight of masses hanging over a pulley in the end we can use light Gates photo gates to measure the acceleration between two points then change the weight on the string just remember that whatever Mass you take off the hanger must go on the trolley itself as the force is accelerating both the trolley and the masses themselves we draw a graph of force against acceleration and it should be a straight line through the origin proving the proportional relationship between F and a the gradient should give you the total mass of the trolley and slotted masses
• 16:30 - 17:00 Newton's third law however is always true and this is the one that people get confused about understandably for every action of force there is an equal and opposite reaction force but this is not referring to balanced forces it's all about perspective when we think about the first two laws we only really consider the object itself for example the force pulling downwards on the ball is its weight even if there is a resistance there's a resultant Force downwards however if you zoom out and think about the Earth to well we know that the Earth is pulling down the ball
• 17:00 - 17:30 but Newton's third law says the complete opposite is true as well the ball is also pulling the Earth up now the Earth is so massive that it doesn't really have an effect but it's still true nevertheless another example if you have two ice skaters if the guy skater pushes on the girl skater there's an equal and opposite reaction force pushing back on him too that's why they both move away from where they were the faster you go the more momentum you also have momentum
• 17:30 - 18:00 is similar to inertia you can think of it as being a measure of how hard it is to get something to stop here's the equation momentum is equal to mass times velocity the unit therefore is kilogram m/s momentum is a vector which means you have negative momentum if your velocity is negative in a collision kinetic energy isn't always conserved but total momentum always is that means whatever the total momentum of the objects was before there must be the same total momentum afterwards as well calculations on this can be tricky but you just have
• 18:00 - 18:30 to be careful with your pluses and minuses you write down M1 U1 if there's just one object moving to begin with remember U from suat we can use it here too and on M2 U2 if there's a second object moving too this then is the total momentum before the Collision before the event this could also be zero if nothing's moving to begin with say a cannon about to fire then all we have to say is that this is equal to the total momentum afterwards M1 V1 for one object plus M2 V2 if there's second object moving two if they've coupled together
• 18:30 - 19:00 we just say m * V where m is the total mass of the two then all you have to do is pop your numbers in making sure that everything traveling to the left say has a negative velocity and you'll be left with one unknown rearrange to find it you get your answer incidentally in the case of the Cannon as there's zero total momentum before the same must be true after too even though the cannon ball is moving that must mean the cannon has the same momentum but in the opposite direction so they still add up to zero this is an example of recoil just for
• 19:00 - 19:30 triple force and momentum are closely linked Newton's second law says that FAL ma but we also know that a is equal to Delta V / T so actually it's also true that force is equal to change in momentum over time or we can say the rate of change of momentum the shorter the time taken for momentum to change the bigger the force needed or felt that's why we use seat belts airbags and crumble zones in cars your change in momentum is the same when you use them but they increase the time taken for
• 19:30 - 20:00 this to happen so a smaller force is felt you're more likely to survive it's just two ways of looking at forces the bigger the force the faster the acceleration or deceleration and so that also means the faster momentum changes too electricity is one of those topics that people find confusing so let's try and demystify it shall we electricity is the flow of charge or charges like electrons they carry energy from a source of energy to a component where the energy is released as another type of energy here's a simple circuit we
• 20:00 - 20:30 have a cell here this is the symbol for that this is the symbol for a battery that's just several cells connected in line we draw straight lines for the wires which in this case are going to a lamp a light bulb and that lights up of course you have to have complete Loops of components and wires in order for these charges to flow by the way you're going to see me mix up cells and batteries in this video because they're just the same thing really and they do the same job leave an angry comment below if you're really that mad about it so what's going on here in this circuit the battery has a store of chemical
• 20:30 - 21:00 potential energy when connected in a complete circuit this energy is transferred to the electrons which moves through the wires this movement of charge is called a current and we say it always goes from the positive terminal of the battery to the negative don't think about it too much as the electrons pass through the bulb their energy is converted into light and some heat too probably as they're never 100% efficient this light and heat is then transferred to the surroundings including your eyes so you can see it but the electrons don't just disappear once they transfer
• 21:00 - 21:30 all the energy to the bulb as this is one big loop these electrons are pushed back round to the battery by the ones behind them where they're refilled with energy ready for another trip around the circuit this constant flow of electrons transferring energy is what keeps the light bulb on because electrons are so small and there are so darn many of them we don't deal with individual electrons but instead deal in kums of electrons or of charge similar to moles in chemistry it's just a specific ific number but we don't care what the number
• 21:30 - 22:00 in a Kum is potential difference PD for short also known as voltage tells us how much energy is transferred per Kum of electrons so if a cell or battery says it's 1 volt that means that one Jewel of energy is given to every Kum of electrons that pass through it if a battery is 6 volts that means six jewles is supplied per Kum instead we measure PD with a voltmeter voltmeters always get added L to a circuit as they're always connected in parallel to the components you want to measure the
• 22:00 - 22:30 voltage of in the real world that means the leads or cables from the voltmeter always piggy back into other leads if we put the voltmeter across the battery it should measure 6 volts right because 6 volts is supplied to the electrons in the circuit that's just 6 Jews per Kum but put it across the bulb and it should still say 6 volts why because the electrons have to lose all of that 6 volts worth of energy as they pass through okay it might be minus 6 Vols but we don't care about minus is really when it comes to PD we only care about
• 22:30 - 23:00 the number here's the equation for PD PD in volts is equal to energy in Jews divided by charging kums in simple form V is equal to e over or divided by q q is the symbol for charge but it's measured in C in kums you'll see the rearranged version eal QV on your formula sheet current on the other hand tells us what the rate of flow of charge is essentially how fast is charge flowing through a c circuit or a component like any equation for a rate
• 23:00 - 23:30 as per usual it's something divided by time so here it's current in amps equals charg in kums divided by time in seconds or i = q / T yes we use capital i as the symbol for current not C blame the French for that as they called current intensit cant it does mean though that we don't get confused between current and kums though so we stick with it you're going to see the rearranged version of this equation on your formula sheet qal I i t that's I * T we measure
• 23:30 - 24:00 current with an ameter note that it's not amp meter unlike a voltmeter it must go in series that means in line with the component we want to measure the current for components in a circuit have resistance that is they resist the flow of charge or current through them but that's not a bad thing this has to happen in order for them to work a bulb has resistance which causes energy to be transferred and light to be emitted a resistor of course has resistance too but it just produces heat when current flows through it if we make a circuit
• 24:00 - 24:30 with a resistor and change the PD available to it what we find is that an increasing PD results in a greater current flowing in fact doubling one doubles the other so we can say that PD and current or V and I are directly proportional drawing a graph of these two makes a straight line and if we turn the battery round we can get Negative values for both two but still a straight line through the origin this straight line a constant gradient shows that a resistor has constant resistance we say it's omic the steeper the gradient of
• 24:30 - 25:00 this line the lower the resistance of the resistor as more current is Flowing per volt the equation for resistance is ohms law V equal I that's PD in volts equals current in amps time resistance in ohms that's the unit for resistance we can get the resistance of a component from an IV graph like this by just picking a point on the line and rearranging ohms law so R is equal to V / I for a resistor you'll end up with the same answer no matter what point you
• 25:00 - 25:30 pick if you repeat the same experiment for a bulb in place of the resistor however you'll end up with a curved graph like this this shows that the resistance is changing the resistance of the metal filament in the bulb in fact you'll find that any metal has a change in resistance if you increase the PD and current they're nonic at higher PDS the current increases less and less so that means they can't be proportional this shows that the resistance of the metal is increasing with the higher PD and higher current the change in gradient shows us
• 25:30 - 26:00 that this is true but we still just take a point on the line and use 's law if we want to find the resistance it's just that it does matter where you pick that point in this case so why does resistance change for a metal well it's because Metals consist of a lattice or grid of ions surrounded by a sea of delocalized electrons that just means they're free and free to move or rather they're fairly free to move because they do collide with the ions as they flow that's why the metal heats up when you pass a current through it the higher the
• 26:00 - 26:30 current the more frequent these collisions are and this makes the ions vibrate more and more which in turn makes it harder for the electrons to flow the resistance has increased now there is another component called a diode it will give you this graph the circuit symbol might give you a clue as to why this is a diode only lets current flow through in One Direction we say that in One Direction the resistance is very high and it's very low in the other which is why the current increases Suddenly at around 1 volt an LED is a
• 26:30 - 27:00 light emitting diode similar symbol just with a couple of extra bits these are what most lights in electronics are these days rather than filament lamps they act in the same way as a diode so they give you the same graph but they just happen to emit light as well we can do another practical on Resistance by measuring V and I for a length of metal wire connected to a circuit with crocodile Clips to calculate resistance of the wire using ohms law then we can move One Clip further up the wire to see how the length of this wire affects resistance you should end up with a straight line through the origin showing
• 27:00 - 27:30 that resistance and length of wire are directly proportional series and parallel circuits this is where things get a bit tricky remembering what happens to current PD and resistance when we have components in series or in parallel here's the simplest series circuit we can make really just two resistors in line with the battery what you need to remember is that for components in series total PD is shared between them current is the same for all of them and the total resistance is just the sum of all resistances that just means added up let's deal with that
• 27:30 - 28:00 first point if these resistors are the same let's say 10 ohms each then that 6vs total PD from the battery must be shared between them so if we put a voltmeter across each of these they'd both read 3 volts it wouldn't matter what resistance these resistors are they could be a million ohms each if they're the same then that total PD is shared equally by the time the electrons leave the second resistor they have to have lost all six volts worth of energy ready to go back to the battery to be refilled way we can also call this setup a potential divider circuit as the total
• 28:00 - 28:30 potential total PD is being shared if the resistors don't have the same resistance then we can use the second point to help us that is the current is the same for both let's say the first resistor is 20 ohms using 4 volts of the total six volts available we know two things out of v i and r so let's use 's law to find out the third for it current in this case I rearranging Oh's law we get I is equal to V / R so that's 4 ID 20 0. 2 amps same for the second resistor too is there also a second
• 28:30 - 29:00 thing we know about the other resistor why yes there is remembering the first rule up here we know that if the first resistor is using four volts of the total six volts available well then the other resistor must be using up 2 volts we could then use ohms law again to find its resistance 10 ohms the rule of thumb is this the greater the resistance the greater the share of the total PD it gets we can also use Oh's law for a whole circuit we just need to make sure that we're dealing with the total PD total current and total resistance the
• 29:00 - 29:30 rules for parallel circuits are the opposite the PD is the same for every Branch current is shared between each branch and the more resistors you add in parallel the lower the total resistance this by the way is because you're giving the current more roots to move through the circuit which means more current can flow so if these two resistors are connected to the 6volt battery in parallel you know straight away that the PD for both has to be 6 Vols voltage isn't shared in parallel circuits if however we say 0.5 amps total current
• 29:30 - 30:00 is flowing through the battery and 0.2 amps of that is flowing through the top resistor that must mean that there's 0.3 amp flowing through the bottom resistor if you're not in a rush why not pause the video and see if you can calculate these two resistances by the way if you want a little bit more help on this then have a look at my video how to answer any electricity question it's not only metals that can change resistance we can have a thermister and you have a circuit that responds to changes in temperature a therm's resistance decreases if the
• 30:00 - 30:30 temperature increases so in essence it does the opposite to a metal in this case if the temperature increased the resistance of the thermister would go down as does its share of the total PD that means the PD measured by this voltmeter will increase this could be the basis of a temperature sensor for your central heating for example an ldr is a light dependent resistor very similar to a thermister but resistance goes down with increased light intensity not temperature so this circuit could be
• 30:30 - 31:00 on the top of a street lamp light intensity goes down resistance of the ldr goes up as does its share with of voltage this could then be connected in some way to the light bulb so it turns on as it gets dark magnetism and electromagnetism a permanent magnet is a metal in which the molecules are permanently aligned in such a way that they produce a magnetic field which can exert a force on particles in other objects and also electrons we give the two ends of a magnet the Nam North and South Pole short for North facing and
• 31:00 - 31:30 south facing poles because that's the way they would point to line up with the Earth's magnetic field so if we made it float you can use iron filings or mini compasses placed around a magnet to visualize its magnetic field magnetic field lines are always complete Loops even though we don't draw them inside the magnet and they never touch these ones going out the ends here will eventually loop back around if we carried on drawing them the direction of magnetic field lines is always from North Pole to South Pole an induced magnet is a material usually
• 31:30 - 32:00 a metal whose particles aligned temporarily when placed in a magnetic field so it makes its own magnetic field hence why an iron nail can be attracted to both the North or South Pole of a permanent magnet we say iron is magnetic but it is not a magnet Cobalt and nickel are also magnetic copper and aluminium for example are not bring two permanent magnets together and they will attract if opposite poles are facing and they will repel if like poles are facing a current flowing through a wire will
• 32:00 - 32:30 produce its own magnetic field we draw the field lines as concentric circles around it using our right hand to help us remember which way the field goes we use the letter B as a shorthand for a magnetic field by the way as well as in the equation coming up the motor effect is when such a wire is in another magnetic field and it will experience a force the equation is f Bill where f is force I is current in amps L is length of the wire in the magnetic field and B is the magnetic flux density essentially
• 32:30 - 33:00 the magnetic field strength this is measured in Tesla note that this equation only works as it is if the current and magnetic field lines are perpendicular to each other but maybe it is worth remembering that if the wire is parallel to the field lines it will experience no Force to find out the direction of the force however on The Wire we use Fleming's leftand rule your thumb is force first finger is field middle finger is current make a janky gun with them where they're all perpendicular and Bam freeze FBI just
• 33:00 - 33:30 twist your wrist to line up your fingers with the current and the field always North Pole to South Pole and the way that your thumb is pointing is the direction of the force on the wire in this case upwards to measure the size of the force in reality we can put the magnet on a balance due to Newton's third law the magnet will also be pushed down with the same Force calculate the force from the fake mass measured use an ameter to get the current and a ro to measure the length of the wire and boom you can calculate the magnetic flux
• 33:30 - 34:00 density between the poles of your magnet electric motors of course employ the motor effect by using a coil of wire that experiences opposite forces on both sides causing it to turn however the current must be reversed every half a turn otherwise it would just stop at the vertical position in this case so that's why we have what we call a split ring commutator to reverse the current every half a turn to make a motor turn faster you can increase the current use a stronger Magnet or add more turns to the coil so there's a greater length of wire ultimately experiencing the force a
• 34:00 - 34:30 loudspeaker is in essence just a motor that goes back and for instead of round around the varying current due to the signal from the music plays say will cause the coil to vibrate back and forth and that's attached to the speaker cone which then produces sound waves in the air double people you're actually done but don't forget to leave a like before you leave here a magnet will cause a current carrying wire to move but the opposite is also true a wire that's moved through a magnetic field will result in a current being induced in it the electrons will move to be more
• 34:30 - 35:00 precise we should say a potential is induced in it essentially voltage this can be called the Dynamo or generator effect a generator itself looks like a motor urn the coil and a potential will be induced in the coil this is basically how power stations work the steam made from burning fuels or nuclear fision turns the turbine which turns this coil as you can see we don't need a split ring commutator it still works all that it means is that it's an alternating PD that's produced or alternating current
• 35:00 - 35:30 AC to increase the output of a Dynamo or generator just turn it faster or similar to a motor add more turns to the coil or use a stronger magnet I say turn it faster but it's not easy you see the current induced in the coil also produces its own magnetic field and this opposes the turning that led to it being produced to begin with so that's why it requires energy to keep it turning and that makes sense you can't just start it turning and then it just carry on otherwise that would mean you'd be getting energy for nothing but in other
• 35:30 - 36:00 words this means that induced currents or potentials don't like being made some dynos have a split ring commutator or circuitry such that they produce DC instead of AC it will be lumpy DC though similar to a loudspeaker being a back and for motor a microphone is a back and for generator sound waves move the diaphragm back and for which is attached to a coil that moves back and forth around a magnet and that then induces a potential in the coil that signal then travels through the wires to the phone recorder or whatever Transformers are
• 36:00 - 36:30 used in the National Grid to change the voltage at which the electricity is transmitted through the overhead cables the current from a power station is so high that too much energy would be lost due to the resistance in the cables if it just went straight into them therefore A Step up Transformer increases the voltage before it enters the grid this then reduces the current so less energy is lost due to heating the reason one goes up while the other one goes down is because electrical power is equal to voltage or PD time current V * I in an Ideal World the
• 36:30 - 37:00 power in and out of a transformer should be the same that would mean that it's 100% efficient so V and I are inversely proportional we can therefore say that V * I for the primary coil is equal to V * I for the secondary coil this is the basic makeup of a transformer the primary coil is connected to the power station in this case the secondary coil is connected to the overhead cables there are more turns on the secondary coil which means it's a Step up Transformer The Volt volage will increase the current will decrease the
• 37:00 - 37:30 cars are wrapped around a soft iron core get this into your head right now though there is or should be no electricity or current in the core instead the electricity is wirelessly transmitted from one coil to the other how is this well it's because the alternating current in the primary coil produces its own magnetic field and the iron core acts like a guide for it we use iron by the way as it's easily magnetized and demagnetized it works well as a guide this magnetic field then induces a
• 37:30 - 38:00 voltage and current in the secondary coil in order for a current to be induced though a wire must experience a change in the magnetic field which is why we must use AC if we use DC in the primary coil it would make a magnetic field but it would be static which cannot induce a current in the secondary coil the ratio of turns in the coils is equal to the ratio of the voltages if the secondary coil has double the turns it has double the voltage and there for half the current so we can say NP / NS
• 38:00 - 38:30 equals VP / vs you can also flip the whole thing when it comes to rearranging it to find VSS or NS A Step Down Transformer at the other end of the cables steps the voltage back down to a safe a PD of 230 volts which means it must have fewer turns on the secondary coil and that's it hopefully this has been useful leave a like if it has and leave any comments or questions you have below and hey come back here after the exam to let us all know how you got on we'd love to know click on the card to go to the playlist for all six papers
• 38:30 - 39:00 and I'll see you next time all the best