Let's see how quickly we can cover everything you need to know for OCR GCC Physics Paper 1. This is good for higher end foundation tier, double combined and triple that is separate physics, so papers 3, 5 or 7, 2. OCR 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. You should remember this first bit from Chemistry Paper 1. The idea of what atoms are like came about gradually. J.J.
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. Niels Bohr later discovered that electrons exist in shells or orbitals Then James Chadwick discovered that the nucleus must also contain some neutral charges. He called 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 its six protons to make 12. However, you can get a carbon atom with 7 neutrons instead, so its mass is 13. These 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 kilograms per cup, but kilograms per metre cubed. So the equation is this.
Density is equal to mass divided by volume. The symbol we use for density is the Greek letter rho, it's just a P without the E on it. Density is dependent on what particles make up the object, and also how tightly packed together they are.
We know water vapour is less dense than liquid water because even though both made from water molecules, they're more spread out when aghast, so there are fewer of them in every metre 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 density. For dimensions that are a few millimetres in length, a ruler won't be that accurate, as its resolution will likely just be one millimetre.
So you could use vernier calipers instead. They usually have a resolution of 0.1 millimetres, a tenth of a millimetre. Objects that are very, very thin, like wires, need a micrometer instead. They usually have a resolution of 0.01mm or a hundredth of a millimetre. The volume of an irregular object, like a chess piece for example, cannot be calculated from measurements.
Instead, we use a displacement can, also called a Eureka can, after the Greek philosopher Archimedes got into a bath full 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 waterline 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 the particles vibrate around fixed positions. It can also be water where the molecules are still touching but free to move past each other and gas, water vapour, 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 that slots into cylinders made of different metals. We turn the heater on, use a voltmeter to measure the PD and ammeter 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, and 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 rearranged SHC equation. The issue is 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 SHC 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 degrees C, its temperature will remain constant until it's all melted.
Only then will its temperature start increasing again. The same thing happens when it reaches 100 degrees 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 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 E equals mc delta T mass times SHC times 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 latent heat.
SLH of a substance tells you how much energy is needed to change the state of one kilogram of it. For example, the SLH of fusion, that just means melting or freezing, for water to ice is 334,000 joules per kilogram. That means the equation for energy needed to change state is this, E equals ML, energy equals mass in kilograms, times specific latent heat in joules per kilogram.
We know gases consist of particles that are far apart, moving fast and randomly. If you heat the gas, the particles gain kinetic energy and they move faster. This means that they collide with the walls of the container the gas is 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 and V are inversely proportional. One doubles, the other one halves. We can therefore say that P1V1, that's the pressure and volume before the change, is equal to P2V2 afterwards.
We know volume is measured in metres cubed, but pressure is measured in newtons per metre 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 pressure is equal to force divided by area, so the unit for pressure is newtons per metre squared. 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 equals H rho, that's just a Greek letter, times G. H being height of the water column above you, basically depth, times density, times gravitational field strength.
The density of water is 1000 kilograms per meter 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-contact, like magnetism, electrostatic forces and gravity.
This is a new concept in GCSE 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, air resistance and tension. The important thing is that 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 go in opposite directions, one must be negative. So in this case, the resultant force would be three newtons to the right, and that's positive if we've decided that positive is in the right direction. If vectors are at right 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 SOHCAHTOA, to find either one of these angles. Chances are it's going to be tan UU's if any.
If forces are balanced, 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 zero metres per second of course.
This is Newton's first law of 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 travelled 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 kilograms by gravitational field strength, or g, which here on Earth is 9.8 newtons per kilogram. Sometimes we just round that to 10 though, you'll be told which to use in a question.
That means that 1 kilogram 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 using the equation for work done. That's work done equals force times 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 times g times h.
Does that look familiar? It should, because that's the exact same equation for calculating gravitational potential energy. That's gpe gained, to be precise.
Forces can also deform an object. If you pull on a spring that is fixed at one end, it will stretch or extend. Hooke's law states that F equals KE, that's force equals spring constant, sometimes called stiffness, times extension. The unit for spring constant is newtons per metre.
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 whatever happens to one happens to the 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's 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 eye level with the bottom of the spring when measuring against the 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 ke squared. Something was attached to the spring and you let go. that object would gain the same amount of kinetic energy, at least in an ideal or closed system.
That is, no energy is lost to 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 times distance to the pivot. So the unit just ends up being Newton metres. 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 anti-clockwise, 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 metres per second, while velocity also has direction. So it could be positive or negative, or up and down, left and right. Here are some typical speeds for when you're travelling.
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. Here's the equation too.
The unit of acceleration is metres per second 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 graph has a constant negative 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 metres per second squared, the same as gravitational field strength, because they are the same thing. A velocity-time graph can also give you the distance travelled. You get that by calculating the area under the graph. Any area under zero metres per second counts as negative displacement, by the way.
That's where the area of both these triangles in this graph adds up to zero. That makes sense though, doesn't it, seeing that it's gone back from whence it came. i.e. your hand.
Suvat 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 zero 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 metres per second squared. For any question involving 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 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, mass times 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 practical. We use a trolley on a track being pulled 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. 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 air resistance, there's a resultant force downwards.
However, if you zoom out and think about the Earth too, well, we know that the Earth is pulling down the ball, 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 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 meters per second.
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 to be careful with your pluses and minuses.
You write down M1U1 if there's just one object moving to begin with, remember U from Suvat we can use it here too, and on M2U2 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. M1V1 for one object, plus M2V2 if there's a second object moving too. If they've coupled together, we just say m times 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 travelling 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 two, even though the cannonball 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 triple, force and momentum are closely linked.
Newton's second law says that F equals MA, but we also know that A is equal to delta V over 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 seatbelts, airbags and crumple zones in cars.
Your change in momentum is the same when you use them, but the increase the time taken for 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 a 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 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 then? The battery has a store of chemical potential energy. When connected in a complete circuit, this energy is transferred to the electrons, which move 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 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 are 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 coulombs of electrons, or coulombs of charge.
Similar to moles in chemistry, it's just a specific number, but we don't care what the number in a coulomb is. Potential difference, PD for short, also known as voltage, tells us how much energy is transferred per coulomb of electrons. So if a cell or battery says it's one volt, that means that one joule of energy is given to every coulomb of electrons that pass through it.
If a battery is six volts, that means six joules is supplied per coulomb instead. We measure PD with a voltmeter. Voltmeters always get added last to a circuit as they're always connected in parallel to the components you want to measure the voltage of.
In the real world, that means the leads or cables from the voltmeter always piggyback 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 joules per coulomb.
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 volts, but we don't care about minuses really when it comes to PD, we only care about the number. Here's the equation for PD.
PD in volts is equal to energy in joules divided by charge in coulombs. 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 coulombs.
You'll see the rearranged version E equals 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 circuit or a component. Like any equation for a rate, as per usual, it's something divided by time. So here it's current in amps equals charge in coulombs divided by time in seconds, or I equals Q divided by T.
Yes, we use capital I as the symbol for current, not C. Blame the French for that, as they called current intensité de courant. It does mean, though, that we don't get confused between current and coulombs, though, so we stick with it. You're going to see the rearranged version of this equation on your formula sheet, Q equals IT.
That's I times T. We measure current with an ammeter. 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 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 too, 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 ohmic. The steeper the gradient of this line, the lower the resistance of the resistor, as more current is flowing per volt.
The equation for resistance is Ohm's law. V equals IR. That's PD in volts equals current in amps times 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 and rearranging Ohm's law, so R is equal to V over I. For a resistor, you'll end up with the same answer no matter what point you 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 changing resistance if you increase the PD and current. They're non-ohmic.
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 a higher PD and higher current. The change in gradient shows us that this is true, but we still just take a point on the line and use Ohm'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 C which... of delocalised 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 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 circus 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 one volt. An LED is a light emitting diode, similar to 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 Ohm's 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 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 add it up. Let's deal with that first point. If these resistors are the same, let's say 10 ohms each, then that 6 volts 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 6 volts worth of energy, ready to go back to the battery to be refilled. By the way, we can also call this setup a potential divider circuit, as the total 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 four volts of the total six volts available. We know two things out of V, I and R. So let's use Ohm's law to find out the third for it current in this case I. Rearranging Ohm's law we get I is equal to V over R.
So that's four divided by 20. 0.2 amps. Same for the second resistor too. Is there also a second 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 4 volts of the total 6 volts available, well then the other resistor must be using up 2 volts. We could then use Ohm's 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 Ohm's law for a whole circuit, we just need to make sure that we're dealing with the total PDE, total current and total resistance. The rules for parallel circuits are the opposite.
The PDE 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 are giving the current more routes to move through the circuit, which means more current can flow. So these two resistors are connected to the 6V battery in parallel.
you know straight away that the PD for both has to be 6V. Voltage isn't shared in parallel circuits. If, however, we say 0.5A total current is flowing through the battery, and 0.2A of that is flowing through the top resistor, that must mean that there's 0.3A 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 thermistor and you have a circuit that responds to changes in temperature. A thermistor's resistance decreases if the temperature increases. So in essence, it does the opposite to a metal. In this case, if the temperature increased, the resistance of the thermistor 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 thermistor, but resistance goes down with increased light intensity, not temperature. So this circuit could be on the top of a street lamp.
Light intensity goes down, resistance of the LDR goes up, as does its share of the 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 names North and South Pole, short for North-facing and 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 visualise 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 a metal, whose particles align 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 repel if like poles are facing. A current flowing through a wire will produce its own magnetic field. 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 field.
flux density, essentially 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 left-hand 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 twist your wrist to line up your fingers with the current in 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 amateur to get the current and a ruler to measure the length of the wire and boom, you can calculate the magnetic flux 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 loudspeaker is in essence just a motor that goes back and forth instead of round and round. The varying current due to the signal from the music player 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 yeah. 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 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. You turn 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 fission 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 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 words, this means that induced currents or potentials don't like being made. Some dynamos have a split ring commutator or circuitry such that they produce DC instead of AC.
It will be lumpy. similar to a loudspeaker being a back and forth motor a microphone is a back and forth generator sound waves move the diaphragm back and forth 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 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, times current, V times I. In an ideal world, the 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 times I for the...
The primary coil is equal to V times 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 voltage will increase, the current will decrease. The coils 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 magnetised and demagnetised. It works well as a guide. This magnetic field then induces a 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 therefore half the current. So we can say NP divided by NS equals VP divided by VS. You can also flip the whole thing. when it comes to rearranging it to find VS or NS.
A step down transformer at the other end of the cables steps the voltage back down to a safer PD of 230V, 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, and I'll see you next time. All the best.