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Which of the following does not change in a transformer?
Current
Voltage
Frequency
All of above
Frequency
A transformer is a static electromagnetic device that transfers electrical energy between two circuits through electromagnetic induction. Throughout this energy conversion process, the supply frequency remains constant because the input and output voltages are linked to the same magnetic flux variation rate, which is governed by the source frequency.
A transformer is a static electromagnetic device that transfers electrical energy between two circuits through electromagnetic induction. Throughout this energy conversion process, the supply frequency remains constant because the input and output voltages are linked to the same magnetic flux variation rate, which is governed by the source frequency.
E=4.44fN╬жmтАЛ тАФ EMF equation showing dependency on frequency (f)
f1тАЛ=f2тАЛ тАФ Fundamental condition of steady-state transformer operation
The transformer operates on Faraday's law of electromagnetic induction. When an AC voltage V1тАЛ is applied to the primary winding, it produces a time-varying magnetic flux ╬ж in the core. Since the same core links both windings, the induced EMFs in the primary and secondary coils share the same temporal variation, forcing the output frequency to match the input frequency (f1тАЛ=f2тАЛ).
Transformers are constant-frequency devices.
Voltage and current are scaled inversely based on the turns ratio a=N2тАЛN1тАЛтАЛ.
Power remains theoretically constant (ignoring losses), hence V1тАЛI1тАЛтЙИV2тАЛI2тАЛ.
Efficient voltage level adjustment for power transmission
Provides galvanic isolation between circuits
Large size for low-frequency applications
Fixed frequency operation only (cannot be used for DC)
Power grid voltage step-up/step-down
Impedance matching in electronics
Changing the frequency would fundamentally alter the magnetizing current (ImтАЛ=2╧АfLmтАЛVтАЛ) and flux density, potentially leading to core saturation.
Option A and B are incorrect because transformers are specifically designed to change voltage and current levels via electromagnetic induction.
C is correct тАФ Frequency is the only electrical parameter that remains constant across the input and output windings of an ideal transformer.
Always remember that transformers act as impedance transformers: Z2тАЛ=Z1тАЛ(N1тАЛN2тАЛтАЛ)2. This is a frequent derivation required in competitive exams.