Current-Voltage Characteristics
Physics: AQA A Level, topic 5.1.2
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.
Test yourself on Current-Voltage Characteristics
What does the current-voltage graph look like for an Ohmic conductor?
Which of these are properties of an Ohmic conductor?
When will current flow in reverse in a semiconducting diode?
Which of these statements are true of diodes?
What is the relationship between current and voltage for a filament bulb?