Current-Voltage Characteristics

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Ohmic Conductor

Ohmic conductors always obey Ohm's law.

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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.
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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.

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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.
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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.

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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.
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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.

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