When a diode is reverse–biased, it prevents current from flowing.

When a diode is forward–biased, it allows current to flow.

The threshold p.d. is the potential difference at which a diode allows current to flow.

A fuse is a component that has a wire that melts if the current is too high.

In a solid metal, the regular and repeating pattern that metal ions are arranged in is known as an ion lattice.

Interpreting I–V graphs

Combined science

Measuring the resistance of a filament lamp

Resistance of a hot metal

Measuring the resistance of a diode

Potential divider circuits

LDRs and thermistors

In the Mains electricity unit, they will build on this knowledge to learn about the dangers of mains electricity, how to use mains electricity safely, the equations I=Q/t, V=E/Q and P=IV, and about the transmission of power in the national grid, including transformers.

In the Electric fields and circuit calculations unit, pupils learnt about the properties of electric fields, moving electric charge, and how to analyse series and parallel electrical circuits.

This unit explores current, resistance, and potential difference. It covers circuit design for lamps, diodes, and thermistors, and emphasises planning experiments, data interpretation, and presenting scientific conclusions.

Circuit components

The characteristics of which component are shown by this I-V graph?

The characteristics of a diode are shown by this I-V graph. What is its threshold voltage?

Which component has a current that increases as the p.d. across it increases, but at higher p.d.s the current does not increase as much as expected?

Which component has an I-V graph that shows the current is directly proportional to the p.d. across it?

What is the most appropriate fuse rating for a device that normally uses a current of 9 A?

metal ions do not vibrate more vigorously

What happens inside a metal wire with a bigger current through it?

to provide a constant resistance to current

to allow current to flow in only one direction

the diode will make the current flow backwards

the diode is connected to a switch that has been turned off

the p.d. across the diode is the wrong way round for current to flow

the p.d. across the diode is the right way round for current to flow

What does it mean when a diode is in reverse bias?

Which of these has a symmetrical I-V graph for both positive and negative p.d.?

it allows less current than expected to flow as the p.d. is increased

it heats up and melts when too much current flows

Which of the following correctly describes how a fuse wire works?

What is the resistance of a diode if it allows 0.16 A to flow when the p.d. across it is 0.8 V?

the resistance varies depending on temperature

the resistance varies depending on light level

the resistance varies depending on the direction of the applied p.d.

the resistance varies depending on the way the experimenter turns a dial

Interpreting I–V graphs

Lesson outcome