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

(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)