# MCQs on Application of EMI (Motor, Dynamo, Transformer) ### Electromagnetic Interference Examples with Answers:

Ques: If a coil made of conducting wires is rotated between poles pieces of the permanent magnet. The motion will generate a current and this device is called
(a) An electric motor
(b) An electric generator
(c) An electromagnet
(d) All of above

Ans. (b)

Ques: In a transformer, the number of turns in primary and secondary are 500 and 2000 respectively. If current in primary is 48 A, the current in the secondary is
(a) 12 A
(b) 24 A
(c) 48 A
(d) 144 A

Ans. (a)

Ques: Core of transformer is made up of
(a) Soft iron
(b) Steel
(c) Iron
(d) Alnico

Ans. (a)

Ques: Quantity that remains unchanged in a transformer is
(a) Voltage
(b) Current
(c) Frequency
(d) None of the above

Ans. (c)

Ques: In a step up transformer, 220 V is converted into 200 V. The number of turns in primary coil is 600. What is the number of turns in the secondary coil
(a) 60
(b) 600
(c) 6000
(d) 100

Ans. (c)

Ques: The ratio of secondary to primary turns is 9 : 4. If power input is P, what will be the ratio of power output (neglect all losses) to power input
(a) 4 : 9
(b) 9 : 4
(c) 5 : 4
(d) 1 : 1

Ans. (d)

Ques: An ideal transformer has 500 and 5000 turn in primary and secondary windings respectively. If the primary voltage is connected to a 6V battery then the secondary voltage is
(a) 0
(b) 60 V
(c) 0.6 V
(d) 6.0 V

Ans. (a)

Ques: A step-up transformer has transformation ratio of 3 : 2. What is the voltage in secondary if voltage in primary is 30 V
(a) 45 V
(b) 15 V
(c) 90 V
(d) 300 V

Ans. (a)

Ques: The number of turns in the primary coil of a transformer is 200 and the number of turns in the secondary coil is 10. If 240 volt AC is applied to the primary, the output from the secondary will be
(a) 48 V
(b) 24 V
(c) 12 V
(d) 6 V

Ans. (c)

Ques: The efficiency of transformer is very high because
(a) There is no moving part in a transformer
(b) It produces very high voltage
(c) It produces very low voltage
(d) None of the above

Ans. (a)

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Ques: In a transformer the primary has 500 turns and secondary has 50 turns. 100 volts are applied to the primary coil, the voltage developed in the secondary will be
(a) 1 V
(b) 10 V
(c) 1000 V
(d) 10000 V

Ans. (b)

Ques: The alternating voltage induced in the secondary coil of a transformer is mainly due to
(a) A varying electric field
(b) A varying magnetic field
(c) The vibrations of the primary coil
(d) The iron core of the transformer

Ans. (b)

Ques: An ideal transformer has 100 turns in the primary and 250 turns in the secondary. The peak value of the ac is 28 V. The r.m.s. secondary voltage is nearest to
(a) 50 V
(b) 70 V
(c) 100 V
(d)  40 V

Ans. (a)

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Ques: Fan is based on
(a) Electric Motor
(b) Electric dynamo
(c) Both
(d) None of these

Ans. (a)

Ques: In an induction coil with resistance, the induced emf will be maximum when
(a) The switch is put on due to high resistance
(b) The switch is put off due to high resistance
(c) The switch is put on due to low resistance
(d) The switch is put off due to low resistance

Ans. (b)

Ques: In transformer, core is made of soft iron to reduce
(a) Hysteresis losses
(b) Eddy current losses
(c) Force opposing electric current
(d) None of the above

Ans. (a)

Ques: When the speed of a dc motor increases the armature current
(a) Increases
(b) Decreases
(c) Does not change
(d) Increases and decreases continuously

Ans. (b)

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Ques: If rotational velocity of a dynamo armature is doubled, then induced e.m.f. will become
(a) Half
(b) Two times
(c) Four times
(d) Unchanged

Ans. (b)

Ques: The pointer of a dead-beat galvanometer gives a steady deflection because
(a) Eddy currents are produced in the conducting frame over which the coil is wound
(b) Its magnet is very strong
(c) Its pointer is very light
(d) Its frame is made of abonite

Ans. (a)

Ques: Dynamo core is laminated because
(a) Magnetic field increases
(b) Magnetic saturation level in core increases
(c) Residual magnetism in core decreases
(d) Loss of energy in core due to eddy currents decreases

Ans. (d)

Ques: A transformer is based on the principle of
(a) Mutual inductance
(b) Self  inductance
(c) Ampere’s law
(d) Lenz’s law

Ans. (a)

Ques: Use of eddy currents is done in the following except
(a) Moving coil galvanometer
(b) Electric brakes
(c) Induction motor
(d) Dynamo

Ans. (d)

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Ques: A transformer connected to 220 volt line shows an output of 2 A at 11000 volt. The efficiency is 100%. The current drawn from the line is
(a) 100 A
(b) 200 A
(c) 22 A
(d) 11 A

Ans. (a)

Ques: Large transformers, when used for some time, become hot and are cooled by circulating oil. The heating of transformer is due to
(a) Heating effect of current alone
(b) Hysteresis loss alone
(c) Both the hysteresis loss and heating effect of current
(d) None of the above

Ans. (c)