Electrical current depends on resistance and potential difference. Different electrical components have different characteristics. These can be investigated using suitable circuits and apparatus.

The current in a circuit depends on the potential difference and the resistance. It is easy to think of each of these in the following way:

- the current is the flow of electric charges
- the potential difference provides the 'push'
- the resistance restricts the flow of charges

Electric wires are made of metal, which have electrical resistance. The atoms in a solid metal are arranged in a regular lattice structure. The outer electrons from each atom are free to move through the structure, forming a current. However, they may collide with atoms or meet defects in the lattice. This reduces the number of electrons flowing, which reduces the current.

Conductors have a low resistance and insulators have a high resistance.

When a charge moves through a potential difference, electrical work is done and energy is transferred. Potential difference can be calculated using the equation:

potential difference = current × resistance

This is when:

- potential difference is measured in volts (V)
- current is measured in amps (A)
- resistance is measured in ohms (Ω)

One volt is the potential difference when one coulomb of charge transfers one joule of energy.

There is a current of 2.0 A in a component with a resistance of 40 Ω. Calculate the potential difference across the component.

potential difference = current × resistance

= 2.0 × 40

= 80 V

- Question
There is a current of 2.0 A in a component with a potential difference of 12 V across the component. Calculate the resistance of the component.

Rearrange the equation to find resistance and then substitute in the known values.

potential difference = current × resistance