The first thing we must tackle is Ohm's Law and that is what we do here as we introduce the resistor.
Youtube video, suitable whether of not you have the board with you.
See board images.
Tutorial guide for when you have the board with you.
At the core of electronics is something called Ohm’s Law and we are now going to explain it. It’s not that complicated and so much will make sense when we have gone through it. So here goes: In any circuit we have a supply providing the electricity (for us that means a battery here) and a load using it - like a light (and on this board it is a something called a resistor). This load will restrict (reduce) the current flowing round the circuit. How much it reduces this current will depend on how much resistance that it gives. A big load (like a large motor) will give little resistance and allow a large current, while and a small device (an LED light for example) will offer more resistance as less current is needed and too much will damage it. /p>
A lot of the time in electronics we want to add some resistance into a circuit to restrict the current and while we could do this with a light or a motor, a simpler way is to use something called a resistor. This is like a little mini heater and will turn the electrical energy it uses into heat rather than light as the LED does. These resistors can restrict the flow by a very precise and wide-ranging amount - from very little to an enormous amount. The amount it restricts is measured in something called ohms. The larger number of ohms means it restricting the flow by a greater amount.
Flick the rotary switch to position A. This is connecting up the resistor that has a value of 100 ohms. Press and hold the yellow button down and note the voltage and current readings on the meters. The relationship between the volts, amps and ohms is what Ohm’s Law is all about. It states that if we multiple the current by the number of ohms we will get the voltage. The current must be in amps not multi-amps, so for example 20mA would be 0.020A (amps). Try doing the maths yourself. It will work out, but don’t forget the meters and the resistor might not be 100% accurate, but you should get a value close to 100.
Here we know all three values, but the idea is that if we know only two of the values, we can work out the last one. For example, if we don’t know the current we can divide the voltage by the ohms, or if we don’t know the resistance, we can divide the voltage by the current and that will give us the number of ohms. Once you start playing with electronics you will use this all the time – its’s a real fundamental.
To calculate the total resistance of two resistors connected in series, we add the two values. So, if you move the rotary switch to position B you will find that the current will be half because we have doubled the resistance to 200 ohms. Do the maths to check this, note the voltage might have changed a little but will be similar. Position C of the switch connects two 100 ohm resistors connected in parallel which means the total resistance is halved - so that's 50 ohms. Now the current will be twice what it was when the switch was at position A.
The resistors used here are very small, sometimes we need bigger ones when the current is larger. This is because the resistor is turning the energy into heat and small resistors will get too hot and burn out. The heat can be calculated by multiplying the current and voltage – this gives us the number of watts (power). These resistors are rated at ¼ watt and will burn out if the wattage is greater than this value Calculate the wattage given off by the first resistor when the switch is in position A. If we use two resistors of the same value (as we are when the switch is in position B and C), each resistor is using half the total wattage.
If you are looking online, you will find that the letter I is used for the current not the letter A as I have done here. It's just how it's done and a good habit to get into. I used A here just to keep it as simple as possible.
Some follow-up ideas to try...
At the core of electronics is something called Ohm’s law and we are now going to explain it. It’s not that complicated and so much will make sense when we have gone through it. Ok here goes, in any circuit we have a ‘supply’ providing the electricity and a ‘load’ using it. This load will restrict the current following round the circuit. How much is it will reduce the current will depend on how much resistance the load gives. A big load will have a big resistance and a small one will offer little resistance. Sometimes we want to add some resistance into a circuit and while we could do this with a light or a motor, a simple way is to use something called a resistor. This is little a mini heater and will turn the energy into heat. These resistors can restrict the flow but a very precise and wide-ranging amount from very little to an enormous amount. This is measured in something called ohms. The larger the number of ohms the move it is restricting the flow. Flick the rotary switch to position A. This is connecting the resistor that has a value of 100 Ohms. Press and hold the yellow button down and note the voltage and current readings. The relationship between the number of Volts, amps and Ohms is what Ohm’s law is all about. It states that if we multiple the current by the number of Ohms we will get the voltage. The current must be in amps not multi-amps, so for example 20mA would be 0.020 amps. Try doing the maths to for yourself. It will work out, but don’t forget the meters and the resistor might not be 100% accurate.
The idea here is that if we know two of the values, we can work out the last one. For example, if we don’t know the current we can divide the voltage by the ohms, or if we don’t know the resistance, we can divide the voltage by the current and that will give us the number of Ohms. Once you start playing will electronics you will use this all the time – its’s a real fundamental.
The to get the total resistance of two resistors connected in series we add up the two values, so if you move the rotary switch to position B you will find that the current will be half because we have doubled the resistance to 200 ohms. Do the maths to check this, note the voltage might have changed a little. Position C of the switch connects two 100 ohm resistors connected in parallel which halves the value, so the current here will be twice what it was when the switch was at position A.
The resistors here are very small, sometimes we need bigger ones, this is when the current is larger because the resistor is turning the energy into heat and small resistors can burn out. The heat can be calculated by multiplying the current and voltage – this gives us the number of watts. It’s the same maths we mentioned earlier when the load was a motor or a light. These resistors are ¼ watt, calculate the wattage given off by the first resistor when the switch is in position A. Remember the current must be in amps, so for example 20mA would be 0.02 amps.