Chapter 14a

Ohmic and non-ohmic conductors

Conductors allow the flow of charge. A current in a metal conductor is the movement of negatively charged electrons from one point to another. The movement of charge transfers energy.
The direction of the conventional current flow is the direction in which a positive charge would move in a circuit from the positive terminal of the battery. Current flow is measured using an ammeter placed in series.

One ampere of current is one coulomb of charge flowing for one second.

For current to flow there must be two things:
an energy source and
an uninterrupted conducting path for current.

Usually there is also a load, a light bulb for example, where the electrical energy is transformed into another useful form such as light or heat.


Components in a circuit use energy, they oppose current flow. This opposition is the resistance of the component measured in ohms. Conductors in which there is a linear relationship between applied voltage and current flow are said to be ohmic. The resistance for ohmic conductors can be found from the gradient of the voltage-current graph or using the following formula of Ohmís law:

The resistance of a conductor depends on its material, its length and its area of cross-section:


This is how temperature alters the resistance in different materials.


Ohmic conductors have a linear relationship between voltage and current, but non-ohmic conductors do not.


For non-ohmic conductors, the resistance cannot be found from the gradient of the voltage-current graph. The resistance has to be calculated by using corresponding voltage and current values.


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