AC generator and Transformer

1. Electrical energy is transmitted over large distances at high alternating voltages. Which of the following statements is not correct?

• For a given power level, there is a lower current.

• Lower current implies less power loss

• Transmission lines can be made thinner

• It is easy to reduce the voltage at the receiving end using step-down transformers.

1. In an ac generator, a coil with N turns, all of the same area A and total resistance R, rotates with frequency ω in a magnetic field B. Then the maximum value of emf generated in the coil is :

• NABR

• NABω

• NABRω

• NAB

1. Which quantity is increased in a step-down transformer?

(a) (b) Voltage (c) (d)

• Current

• Voltage

• Power

• Frequency

1. A transformer is used to light a 100 W and 110 V lamp from a 220 V mains. If the main current is 0.5 A, the efficiency of the transformer is approximately:

• 30%

• 50%

• 90%

• 10%

. The core of a transformer is laminated as :

• it improves the ratio of voltage in the primary

  and secondary may be increased.

• it checks rusting of the core may be stopped.

• it reduces energy losses due to eddy currents.

• it increases flux linkage.

If rotational velocity of an armature is doubled, emf

generated in a generator will be :

• Half

• Two times

• Four times

• Unchanged

The output of a step-down transformer is measured

to be 24 V when connected to a 12 W Light bulb.

The value of the peak current is : 

• (1/ 1.414) A

• 1.414 A

• 2 A

• (2 X 1.414) A

Quantity that remains unchanged in a transformer

is :

• Current

• Voltage

• Frequency

• None of the above

Which of the following losses in transformer is also

known as variable loss:

• Copper loss

• Stray loss

• Dielectric loss

• Core loss

A generator produces a voltage that is given by V = 240 sin 120t volt, where t is in

second. The frequency and r.m.s voltage are :

• 60 Hz. & 240 volt

• 19Hz. & 120 volt

• 19 Hz. & 170 volt

• 754 Hz. & 170 volt.