Resistance

Electrons can easily pass through a copper wire; the wire has a small resistance. Current is the flow of electrons, so when the electrons can flow easily there is a big current and a small resistance. Electrons don’t pass as easily through other types of wire, and the longer the wire or the thinner the wire the larger the resistance. Heating the wire will also increase the resistance.

Resistance R is measured in Ohms (W). The potential difference or voltage V is measured in volts (V) and the current I is measured in Amperes (A). The formula below can be used to calculate the resistance of a wire.

The apparatus can be used to find the voltage and the current in order to calculate the voltage.

Ohm’s Law states that as the resistance increases the current decreases. The higher the resistance the greater the voltage needed to push electrons through the conductor.

Any conductor which has a resistance will warm up and give off heat. The hotter the wire gets the larger the resistance. When the electrons pass through the conductor they collide with the atoms of the conductor, making them vibrate more vigorously and warm up.

Heating elements:

Nichrome wire is coiled to take up less space and is used to make heating elements in appliances such as irons. Nichrome has a high resistance and can be kept red hot without oxidising in the air.

Investigation:

What factors do you think will increase the resistance of a circuit?

How do you think changing these variables will affect the resistance?

Which variable will you investigate and which variables will you keep the same?