10 Question-answer on transformer
1. If the number of turns in primary and secondary coil is increased to two times each, the mutual inductance
(a) Become 4 time
(b) Become 2 time
(c) Become 1/4 time
(d) Remains unchanged.
Ans: ( a)
2. A transformer is used to light 140 W, 24 V lamp from 240 V a.c. mains. The current in the main is 0.7 A. the efficiency of transformer is nearest to
(a) 90%
(b) 80%
(c) 70%
(d) 60%
Ans: ( b)
3. In a step down transformer, use of 120 V line, provides a pot. Diff. of 2400 V. if the primary coil has 75 turns, number of turns in secondary coil is:
(a) 150
(b) 1500
(c) 1200
(d) 1575
Ans: (b)
4. A low loss transformer has 230 V applied to primary and gives 4.6 V in secondary. The secondary is connected to a load which draws 5 A current. The current in primary is:
(a) 0.1 A
(b) 1.0 A
(c) 10 A
(d) 250 A
Ans : (a)
5. A transformer connected to 220 V line shows an output of 2 A at 11000 V. the efficiency of the transformer is 100%. The current drawn from the line is:
(a) 100 A
(b) 200 A
(c) 22 A
(d) 11 A
Ans: ( a)
6. Which of the following is correct?
(a) An induction coil has a closed-soft iron core whereas a transformer has a straight soft iron core.
(b) The human body generates electricity
(c) Resistance is reciprocal of conductance
(d) Resistance of the fuse wire is high.
Ans: (c)
7. In an ideal transformer, the voltage is stepped down from 11 kV to 220 V. if the primary current be 100A, the current in the secondary should be:
(a) 5 kA
(b) 1 kA
(c) 0.5 kA
(d) 0.1 kA
Ans: (c)
8. For long distance transmission, the a.c. is stepped up because at high voltage, the transmission is:
(a) Faster
(b) Economical
(c) Undamped
(d) Less dangerous.
Ans: (b,c)
9. The power loss in a transformer working on 220 V a.c. supply is 30%. The ratio of primary to secondary current when output voltage is 110 V is:
(a) 1 : 2
(b) 2 :1
(c) 1 : 1
(d) 5 : 7
Ans: ( d)
10. A transformer has an efficiency of 80%. It works at 4 kW and 100 V. if secondary voltage is 240 V, the current in primary coil is:
(a) 0.4 A
(b) 4 A
(c) 10 A
(d) 40 A
Ans: ( d)