Physics Chapter 9 Entry test MCQs
26. The turn ratio of a transformer is 2:3. If the current through primary is 3A, then current through load resistance is
a. 2A
b. 1A
c. 1.5 A
d. 4.5 A
27. A transformer is used to
a. Convert direct current to alternating current
b. Convert alternating current to direct current
c. Change the level of alternating voltage
d. Convert mechanical energy to electrical energy
28. A transformer is used to light a 100 W and 110 V lamp from 220 V mains. If the main current is 0.5 A, the efficiency of the transformer is approximately.
a. 50%
b. 10%
c. 90%
d. 30%
29. If the current in the primary coil and number of turns in it are Ip and Np respectively and the number of turns and current in the secondary are Ns and Is respectively then the value the of Ns : Np
a. lp : ls
b. ls : lp
c. lp2 : ls2
d. ls2 : lp2
30. The ratio of emf across primary coil to the emf across secondary coil is
a. ls2 : lp2
b. ls : lp
c. Ns : Np
d. None of these
31. In step up transformer, voltage in the secondary increases and power in secondary
a. Decreases because voltage increases
b. Remain same
c. May increases if voltage remain same
d. Increases because current decreases
32. In a transformer heat is produced due to eddy current in
a. Iron core
b. Primary coil
c. Secondary coil
d. All of these
33. ————– is the energy expended to magnetize and demagnetize the core material in each cycle of the A.C.
a. Hysteresis loss
b. Power loss
c. Heat loss
d. All of the above
34. Laminated core in a transformer is used to reduce
a. Iron losses
b. Eddy current losses
c. Heat losses due to resistance
d. Hysteresis losses
35. The loss of power in transformer is due to
a. Resistance of coils
b. Eddy current
c. Magnetic hysteresis
d. All
36. A step-down transformer, transforms 220 volts to 11 volts. If the current in primary and secondary coil are 5A and 90 A respectively, efficiency of transformer is
a. 40%
b. 70%
c. 90%
d. 20%
37. If turns in primary = 50, secondary=200, primary voltage = 120V, primary current 3A,then output power will be about
a. 300 W
b. 360 W
c. Zero
d. 460 W
38. To improve efficiency of transformer the flux coupling between primary & secondary coils should be
a. May be small or may be maximum
b. Small
c. Zero
d. Maximum
39. Primary and secondary coils of a transformer have 50 and 200 turns respectively. When primary is connected to 9-volt battery secondary voltage is
a. 36
b. 90
c. Zero
d. 18
40. The ratio of secondary to the primary turns in a transformer is 3: 2. If the power output be P, then the input power neglecting all loses must be equal to
a. P
b. 5 P
c. 2/5 P
d. .5 P
41. The efficiency of transformer is very high because
a. It produces very low voltage
b. There is no moving part in a transformer
c. It produces very high voltage
d. None of the above
42. A step-down transformer is used on a 1000 line to deliver 20 A at 120 V at the secondary coil. If the efficiency of the transformer is 80% the current drawn from the line is.
a. 0.3 A
b. 3 A
c. 2.4 A
d. 30 A
43. A step-up transformer
a. Increases power-level
b. Decreases current-level
c. Increases voltage-level
d. Both B and C
44. The number of turns in the primary and secondary coil of a step-up transformer are 200 and 500 respectively. If the power in the input is 100 Watt and current 1A then the output power and current will respectively
a. 400 W, 4 A
b. 100 W, 2 A
c. 100 W, 0.4 A
d. 200 W, 0.2 A
PAST PAPER MCQS
45. A transformer changes 12V to 18000 V and there are 6000 turns in the secondary coil. The number of turns in the primary coil are:
a. 30
b. 40
c. 4
d. 20
46. The phenomenon of mutual induction is practically used is
a. Galvanometer
b. Transformer
c. Avometer
d. Generator
47. The phenomenon used for producing emf in coil of generator is;
a. Electrostatic induction
b. Mutual Induction
c. Electromagnetic inductions
d. Self-induction
48. The function of main transformer is to convert:
a. A high value alternating voltage to low value direct voltage
b. One direct voltage to another direct voltage of different magnitude
c. A high value alternating current to low value direct voltage
d. One alternating voltage to another alternating voltage of different magnitude
49. In transmission from grid station, power losses are minimized by:
a. Increasing resistance
b. Increasing current
c. Increasing voltage
d. Decreasing current
50. The domestic electricity supply has a frequency of:
a. 50 Hz
b. 150 Hz
c. 25 Hz
d. 100 Hz
51. Transformer is a device which steps up or steps down the input:
a. Energy
b. Current
c. Power
d. Voltage
52. If a stationary bar magnet is placed near a through the coil, the galvanometer shows: coil at rest so maximum lines of force passes
a. No current
b. Maximum current
c. Intermediate value of curren
d. Minimum current
53. Which is the correct relation:
a. Ns/Np = Is/Ip
b. Ns/Np=Vs/Vp
c. NsNp=Vs/Vp
d. None
54. In a step-up transformer, current across secondary is————.
a. Equal
b. Less
c. More
d. None
55. Find Turn ratio if Vs/Vp=2
a. 4:8
b. 2:1
c. 1:2
d. None