5.1.2

# Current-Voltage Characteristics

Test yourself

## Ohmic Conductor

Ohmic conductors always obey Ohm's law.

### Current-voltage graphs

• A current-voltage graph displays how current and voltage are related.
• The gradient of the current-voltage graph is the reciprocal of the resistance.

### Ohmic behaviour

• An ohmic conductor should have a linear relationship between current and voltage.
• A linear relationship produces a straight line graph.
• At very high voltages and currents, this linear behaviour can break down.
• The conductor is then not ohmic.

## Semiconductor Diode

A diode only allows current to flow in one direction unless there are extreme conditions.

### Reverse bias

• A diode will only let current flow in one direction unless the voltage in the other direction is very large.
• Reverse bias is the direction in which current is not allowed to flow.
• For current to flow in reverse bias, a very large voltage is required.
• The voltage at which current will flow in reverse bias is called the breakdown voltage.

### Forward bias

• Forward bias is the direction that current is allowed to flow.
• The point at which the diode will conduct in the forward direction is called the threshold voltage.
• This is usually about 0.6 V.

## Filament Bulb

The filament bulb is an example of a non-Ohmic conductor.

### Filament bulb

• The current flowing through the filament produces heat.
• The higher the temperature of the filament, the higher the resistance.
• This increase in resistance limits the amount of current that is able to flow through the filament.

### Current-voltage graph

• An increase in the voltage supplied to the bulb does not produce the same increase in the current flowing through.
• The filament bulb displays a non-Ohmic relationship between the voltage and current.