Hint! You should have a secure understanding of current before you try this activity. If not, we recommend that you go back and try out the Understanding Current and Charge activity.
Did you know, when you use an electrical device, it gets hot? You did know because you’ve done the activity on energy transfers on EdPlace? It’s amazing isn’t it – the person that wrote it is so cool. If you haven’t done that worksheet (why haven’t you?) you might have noticed this effect when using your phone. Especially when you are on Wi-Fi, you’ll find it might get hot to the touch. This is because of an electrical effect called resistance. We will be looking at resistance, current and potential difference and how all three of these concepts are related in this worksheet.
First of all, let’s look at what some of those terms mean.
1 – resistance. This is how much the electrons are being slowed down. If you remember, in order to make current you have to move electrons but there is stuff in that way of those electrons. This means that the electrons are being slowed down when they bash into that stuff, reducing the current. More resistance means less current.
2 – potential difference. This is a difference in charge between two places. If you remember, in order to make a current you need a positive and a negative charge. Well, we know how big these charges are by measuring the potential difference between them (measured in volts). If you have a bigger potential difference, then the electrons will be moving quicker. This means that you will have a bigger current.
3 – current. You should already know what this means, but here I want to talk about the 2 different ways you can increase or decrease the current. The first way we have just spoken about – you can make them go faster. The second way is by forcing more electrons to move. Imagine if it is just you walking through a corridor, should be easy right? Now imagine there are 100 of you trying to walk through a corridor – well, that’s a lot more difficult isn’t it. This means there is more resistance if there is more current.
Hopefully, now, you can see that all three of these ideas are linked, and they are linked by the most famous of all of the electrical equations:
INSERT IMAGE OF EQUATION HERE
V = potential difference (measured in volts (V)) – also known as voltage
I = current (measured in Amperes or amps (A))
R = resistance (measured in Ohms (Ω))
Now let’s talk a look at that equation in action:
Q – An electrical circuit has a current of 10 A and a total resistance of 3Ω. Calculate the potential difference needed by this circuit.
Step 1 – highlight all of the number in the equation:
An electrical circuit has a current of 10 A and a total resistance of 3 Ω. Calculate the potential difference needed by this circuit.
Step 2 – Write out the numbers next to their symbols:
V = ?
I = 10 A
R = 3 Ω
Step 3 – put the numbers into the equation:
V = 3 x 10
Step 4 – do the maths and write your answer:
V = 30 V
Don’t forget your units!
Let’s try some questions on that!