Concept:The magnetic effect of an electric current is the ability of a current to set up a magnetic field or interact with one.
Explanation:Among the options, the dynamo is the only device that operates through a magnetic/ electromagnetic action.
In a dynamo, a coil rotates inside a magnetic field, so the magnetic flux linked with the coil changes continuously.
This changing flux induces an electromotive force in the coil, and this force drives an electric current through the circuit.
Therefore the dynamo works by using the interaction between electricity and magnetism.
An electric heater uses the heating effect of current, a photocell uses the photoelectric effect, and a cold cathode is based on electron emission from an unheated electrode.
None of these three devices depends on magnetism as its principle of operation.
Answer:C. Dynamo