# Answer to Question #62148 in Electromagnetism for hamid

Question #62148

is transformer a ohmic or non ohmic device?

Expert's answer

Ohms law applies to any and to all components if there is current flowing. Answer for Ohm's Law to apply, the ratio of voltage to current must remain constant for variations in voltage. This is only true for a limited range of conductors and devices which are termed 'linear' or 'ohmic'. If the ratio of voltage to current changes for variations in voltage, then the conductor or device is 'non-linear' or 'non-ohmic', and Ohm's Law does not apply. An example of a non-ohmic conductor is a lamp filament.

As to whether a transformer obeys Ohm's Law, the answer is not straightforward. When the transformer is not supplying a load, the primary current is determined by the voltage and impedance of the primary windings and, say, doubling the voltage will double the primary current -so you could say that it is obeying Ohm's Law.

However, when the transformer is supplying load, the primary current is determined by the secondary current and not just by variations in the supply voltage, so is clearly not obeying Ohm's Law. Therefore transformers are non-ohmic devices.

As to whether a transformer obeys Ohm's Law, the answer is not straightforward. When the transformer is not supplying a load, the primary current is determined by the voltage and impedance of the primary windings and, say, doubling the voltage will double the primary current -so you could say that it is obeying Ohm's Law.

However, when the transformer is supplying load, the primary current is determined by the secondary current and not just by variations in the supply voltage, so is clearly not obeying Ohm's Law. Therefore transformers are non-ohmic devices.

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