How to affect electric current - OCR 21st CenturyCurrent, potential difference and resistance

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

Learn more on current, resistance and potential difference in this podcast

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Resistance

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.

Calculating potential difference

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)

Example

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