The Physics Question Bank

A diode is a component that acts like a one-way gate for electric current.

It allows current to flow easily in one direction, but it makes it very difficult for current to flow in the opposite direction.

When the diode is connected the correct way round, it is forward biased.

In forward bias, the diode has a low resistance, so current can flow through the circuit.

When the diode is connected the wrong way round, it is reverse biased.

In reverse bias, the diode has a very high resistance, so almost no current flows.

A simple way to remember it is:

correct way round → low resistance → current flows

wrong way round → high resistance → current blocked

For AQA GCSE Physics, the important point is that a diode has a non-linear current–potential difference graph.

This means the current does not increase in a simple straight-line pattern. Current only flows when the diode is connected in the forward direction and the potential difference is large enough.

A strong GCSE answer:

A diode allows current to flow in one direction only. When it is forward biased, it has a low resistance and current can flow. When it is reverse biased, it has a very high resistance, so almost no current flows. This makes the diode useful for controlling the direction of current in a circuit.

For an LED:

An LED is a light-emitting diode. It works like a normal diode, but it also gives out light when current flows through it in the forward direction.