10 Question-answer on transformer

10 Question-answer on transformer | Learn Physics

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

(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%

(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

(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

(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

(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

(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

(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

(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

(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

(d) 40 A

Ans: ( d)

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