You know that the narrower the wire through which electricity passes, the more the resistance it has.
The most common type of resistors called Carbon Film resistors are made up of a carbon tube into which a grooves have been cut.
The grooves mean there is less carbon for the current to pass through, so the resistance can be increased by having a deeper groove.
Learn It
Resistors are colour coded so we can tell what there resistance is.
Most resistors have 4 bands painted on the outside.
Starting at the opposite end to the Gold or Silver band (In this image that would be the right hand side):
The first band gives us the first number
The second band give us the second number
The third band gives us the number of zeros.
The fourth bands gives us the tolerance.
So for example, the resistor pictured above has the colours:
Brown - 1 (First number is 1)
Black - 0 (Second number is 0)
Yellow -4 (4 zeros)
Gold - +/-5%
This means it is a 100000Ω resistor, or what we would normally call a 100kΩ resistor.
The 5% tolerance means that the actual resistance can vary by + or = 5%, which in this case would be 0.05 X 100000 = 5000Ω
2 Assessment
Badge It - Silver
Progress ladder Red, Identify several electronic components, with assistance.
Look at the resistors in this photograph.
For each resistor, use the colour table to identify it's resistance.
3 Ohm's Law
You've seen how increasing the resistance in a wire can effect the current passing through the wire.
It is therefore possible to reduce the amount of current flowing in a circuit, by adding in resistors.
To do this we use Ohm's Law
V=IR
V is for Voltage, I for current and R is for resistance.
We can rearange the equation to make I the subject, which will allow us to calculate the current in a circuit.
Look at the animation below to see how.
So there are three different ways of writing Ohm's Law
4 Assessment
Badge It - Gold
Progress ladder Orange, Identify several electronic components, without assistance.
Copy you own version of this table shown below
Look at the simple circuit detailed below, click on the 'get values' button for 2 of the 3 values needed to calculate the third.
Hit the button to generate a new question. Fill in the provided values into your copy of the table and then caluclate the third value for yourself.
Sometimes the current is described in mA. This is short for milliamps, which are a thousandth of an amp. (Just divide it by 1000 to calculate the current in amps)
