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A DC generator works on the principle of Faraday’s laws of electromagnetic induction.
A magnetizing force and a static magnetic field are produced around a long straight conductor when a DC current passes through it. Magnetic field is greatly intensified if the wire is coiled and produced a static magnetic field around itself. A voltage and current are induced within the coil due to the movement of wire or variation in magnetic field.
Hence the correct option is C.
ADDITIONAL INFORMATION
* Ohm's law states that the current pass through a conductor is directly proportional to the voltage across it.
* Joule heating converts electric energy into heat energy by the presence of resistance in a circuit and produces heat.
Voltages and current in a transformer change but the power remains the same but that is only for an ideal transformer, usually there is a loss in power in the form of heat, sound, vibrations, eddy currents, etc. Only the frequency remains constant. It depends on the number of poles and the speed of the rotating magnet of the generator. Hence, the correct option is C.
The back emf is directly proportional to the speed of the motor in DC motors. The speed of the motor is zero when the motor starts moving. Hence, the back emf will be zero at that point.
Lenz law states that the direction of any magnetic induction effect always tends to oppose the cause which produce it. It is based on the law of conservation of energy. In order to do work against the direction of effect, we need to put more efforts which leads to the periodic change in magnetic flux hence more current will be influenced.
Lenz’s law is used to find the direction of electromagnetically induced electric current.
Hence A is the correct option.
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