Electrician Exam Question Answers 3

Does frequent starting and stopping of fluorescent lighting affect the age of the light?
Answer: Yes, the life of the fluorescent light is affected by the frequent starting and stopping. A bulb that is constantly left over on will have more life compared to that on which are frequently switched on and off.

What is the material used in making core of the transformer?
Answer: Transformer is made of CRGO (cold Rolled Grain Oriented) material to reduce losses.

Do feeders contain circuits connect to them?
Answer: No, feeders are not connected to any circuits in intermediate position.

What causes the induction motor to rotate?
Answer: Motor consists of stator windings and rotor windings.When 3 phase power is supplied to stator of induction motor current flows through the winding and produces flux. This flux will cut the stationary rotor winding and emf is induced in rotor windings. As the rotor windings are short circuited, current starts flowing the rotor windings. This current will produce an magnetic field which opposes the main magnetic field and hence the torque is produced and motor starts rotate.

If a DC motor is rapidly disconnected from the line, what must be provided?
Answer: A means of shorting out of the motor, either directly or through a resistance, so that the collapsing magnetic field does not induce a high voltage.

What is the difference between the alternator and dc generator?
Answer: Both DC generator and Alternator differ in the way in which the power is taken out of the machine. Alternator uses slip rings to take the power out and dc generator uses commutator which converts the bi directional current to unidirectional current.