A **resistor **can be used to change the electric **current **(**I**) in a circuit. It can be a **fixed **resistor or a **variable **one (**rheostat**). The **voltage **(**V**) that a current produces depends on the **resistance **(**R**). The formula that connects current, voltage and resistance is:

The unit of resistance is **ohm **(**Ω**), current (**ampere**, **A**), voltage (**volt**, **V**)

**Uses of resistance**

A piece of wire has a resistance of 5 **Ω** and melts if the current through it exceeds 8** A**. What is the maximum possible voltage that could cross the wire, without melting it?

To answer this, you need to rearrange the equation. For current, it would become: and for voltage it would be **V = I x R**. So, in our question** **V = 8 x 5** = ****40 V**

This is a picture of a resistor:

The current in a circuit must not be allowed to get too high. Electrons bump into the atoms of a resistor, which makes the atoms vibrate more and the resistor get hotter. This makes the flow of electrons difficult and resistance increases. **Filaments **(a tiny thin wire in a light bulb) becomes so hot that it emits light.