Electrical Machines (Transformer)

1) What is the unit of resistance?
A. ohms
B. watts
C. Ampere
D. mho

2) The primary and secondary winding of transformer are linked each other by
A. Conduction.
B. Mutual induction.
C. Not linked at all.
D. Self induction.

3) Which parameter does not change during transformation action in transformer?
A. Voltage
B. Frequency
C. Current
D. None of these

4) Secondary current of a step down transformer is
A. Lower than primary current
B. Higher than primary current
C. Equal to primary current
D. Double than primary current

5) The core of transformer must have
A. Low reluctance
B. High resistance
C. High reluctance
D. Low resistance

6) The working principle of transformer depends upon
A. Ohms law
B. Lenz’s Law
C. Fleming’s left hand rule
D. Faraday’s Law of Electromagnetic Induction.

7) An ideal transformer is one which has
A. No winding resistance
B. No leakage reactance
C. No losses
D. All of above

8) In an ideal transformer the magnetizing current lags behind applied primary voltage by an angle of
A. 90o
B. 75o
C. - 90o
D. 45o

9) In an ideal transformers
A. Both primary and secondary induced emfs are self induced emfs
B. Both primary and secondary induced emfs are mutually induced emfs
C. Primary induced emf is self induced and secondary induced emf is mutually induced
D. Primary induced emf is mutually induced and secondary induced emf is self induced

10) The input power under no load condition of transformer consists of
A. Core losses in transformer
B. core losses and very small amount of copper loss in primary.
C. copper loss in transformers
D. significant amount of copper loss along with negligible amount of core losses.

Answers:
1. a
2. b
3. b
4. b
5. a
6. d
7. d
8. a
9. c
10. b

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