WBCS Mains Physics Electricity & Magnetism Questions 2023

Q17. A soap bubble is given a negative charge, then its radius

(A) Decreases
(B) Increases
(C) Remains unchanged
(D) Nothing can be predicted as information is insufficient

Correct Answer: (B) Increases

Q28. Quantity that remains unchanged in a transformer is

(A) Voltage
(B) Current
(C) Frequency
(D) Current density

Correct Answer: (C) Frequency

Q56. The direction of induced e.m.f. during electromagnetic induction is given by

(A) Faraday’s Law
(B) Lenz’s Law
(C) Maxwell’s Law
(D) Ampere’s Law

Correct Answer: (B) Lenz’s Law

Q86. The Electrostatic Precipitator is ideally used for the removal of which type of pollution?

(A) Outdoor Air pollution
(B) Indoor Air pollution
(C) Water pollution
(D) Odour pollution

Correct Answer: (A) Outdoor Air pollution

Q95. A 220 volt A.C. is more dangerous than 220 volt D.C. because

(A) The A.C. attracts.
(B) The D.C. repels.
(C) The body offers less resistance to A.C.
(D) Peak voltage for A.C. is much larger than 220 volt.

Correct Answer: (C) The body offers less resistance to A.C.

Q103. A magnetic field can be produced by

(A) Moving charge
(B) A changing electric field
(C) Both (A) and (B)
(D) None of the above

Correct Answer: (C) Both (A) and (B)

Q112. The positive temperature coefficient of resistance is for

(A) Carbon
(B) Germanium
(C) Copper
(D) An electrolyte

Correct Answer: (C) Copper

Q147. What is the frequency of supply A.C. (current) in India?

(A) 220 Hz
(B) 60 Hz
(C) 50 Hz
(D) 40 Hz

Correct Answer: (C) 50 Hz

Q149. Which of the following is the most suitable material for making a permanent magnet?

(A) Steel
(B) Soft iron
(C) Copper
(D) Nickel

Correct Answer: (A) Steel

Q151. In a charged capacitor, the energy resides in

(A) Positive charges
(B) Both positive and negative charges
(C) The field between the plates
(D) Around the edge of the plates

Correct Answer: (C) The field between the plates

Q156. Magnetic effect of current was discovered by

(A) Faraday
(B) Oersted
(C) Ampere
(D) Bohr

Correct Answer: (B) Oersted

Q196. Alternating current is transmitted to distant places at

(A) High voltage and low current
(B) High voltage and high current
(C) Low voltage and low current
(D) Low voltage and high current

Correct Answer: (A) High voltage and low current

WBCS Mains Physics Electricity & Magnetism Questions 2022

Q24. The material successfully used as induction core is

(A) Garnet
(B) AlNico magnet
(C) Ba-Sr ferrite
(D) Ni-Zn ferrite

Correct Answer: (D) Ni-Zn ferrite

Q32. Current in a circuit is wattless when the phase difference between current and voltage is

(A) 0
(B) π/2
(C) π
(D) −π

Correct Answer: (B) π/2

Q176. Electrical resistivity of a conductor

(A) Increases with temperature
(B) Decreases with temperature
(C) Does not change with temperature
(D) Decreases at lower temperature, then increases with temperature

Correct Answer: (A) Increases with temperature

WBCS Mains Physics Electricity & Magnetism Questions 2021

Q170. An electric motor

(A) Generates mechanical energy.
(B) Generates electric energy.
(C) Converts mechanical energy into electric energy.
(D) Converts electrical energy into mechanical energy.

Correct Answer: (D) Converts electrical energy into mechanical energy.

WBCS Mains Physics Electricity & Magnetism Questions 2020

Q6. A piece of wire of resistance R is cut into three equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R₁, then the ratio R/R₁ is

(A) 1/3
(B) 1
(C) 3
(D) 9

Correct Answer: (D) 9

Q9. At the time of short circuit, the current in the circuit

(A) Reduces substantially
(B) Does not change
(C) Increases heavily
(D) Varies continuously

Correct Answer: (C) Increases heavily

Q51. Two resistors R and 2R are connected in series in an electric circuit. The thermal energy developed in R and 2R are in the ratio

(A) 2 : 1
(B) 4 : 1
(C) 1 : 4
(D) 1 : 2

Correct Answer: (D) 1 : 2

Q66. Consider the following statements:

(i) An emf can be induced by moving a conductor in a magnetic field.
(ii) An emf can be induced by changing the magnetic field.

(A) (i) is true but (ii) is false
(B) (ii) is true but (i) is false
(C) Both (i) and (ii) are false
(D) Both (i) and (ii) are true

Correct Answer: (D) Both (i) and (ii) are true

WBCS Mains Physics Electricity & Magnetism Questions 2019

Q123. For a metallic wire, the ratio V/i [V = applied potential difference and i = current flowing] is

(A) Independent of temperature.
(B) Increases as the temperature rises.
(C) Decreases as the temperature rises.
(D) Increases or decreases as the temperature rises depending upon the metal.

Correct Answer: (B) Increases as the temperature rises.

Q157. An electric bulb marked as 50 W–200 V is connected across a 100 V supply. The present power of the bulb is

(A) 37.5 W
(B) 25 W
(C) 12.5 W
(D) 10 W

Correct Answer: (C) 12.5 W

Q182. In electromagnetic theory, the continuity equation relates

(A) Volume conservation
(B) Mass conservation
(C) Charge conservation
(D) Energy conservation

Correct Answer: (C) Charge conservation

WBCS Mains Physics Electricity & Magnetism Questions 2018

Q25. If the current passing through a resistance increases by two times, the heat generated will increase by

(A) 2 times
(B) 4 times
(C) 6 times
(D) 8 times

Correct Answer: (B) 4 times

Q45. The device that converts AC to DC is called

(A) Transformer
(B) Rectifier
(C) Induction motor
(D) Dynamo

Correct Answer: (B) Rectifier

Q92. The resistance of an ideal ammeter is

(A) Zero
(B) Small
(C) High
(D) Very high

Correct Answer: (A) Zero

WBCS Mains Physics Electricity & Magnetism Questions 2017

Q114. Iron loses its magnetic property at

(A) Melting point
(B) Curie point
(C) 1000°C
(D) Boiling point

Correct Answer: (B) Curie point

Q154. If two bulbs of 25 W and 100 W rated at 220 V are connected in series across a 440 V supply

(A) 25 W bulb will fuse.
(B) 100 W bulb will fuse.
(C) None of these will fuse.
(D) Both will fuse.

Correct Answer: (A) 25 W bulb will fuse.

Q162. Electronic polarization in dielectric materials occurs at a frequency around

(A) kHz
(B) MHz
(C) GHz
(D) None of the above

Correct Answer: (C) GHz

Q195. (Ni-Mn) ferrite is an example of a

(A) Ferrimagnetic material
(B) Paramagnetic material
(C) Ferromagnetic material
(D) None of the above

Correct Answer: (A) Ferrimagnetic material

Q196. Soft iron is used in many parts of electrical machines for its

(A) Low hysteresis loss and low permeability
(B) High hysteresis loss and low permeability
(C) Large density and large retentivity
(D) Low hysteresis loss and high permeability

Correct Answer: (D) Low hysteresis loss and high permeability.

Q197. Tangent galvanometer is used to measure

(A) Steady currents
(B) Current impulses
(C) Earth’s magnetic field
(D) None of the above

Correct Answer: (A) Steady currents

Q198. In a charged capacitor, the energy is stored as

(A) Positive charge
(B) Both as positive and negative charge
(C) The electric field between the plates
(D) The potential energy of the capacitor plates

Correct Answer: (C) The electric field between the plates

WBCS Mains Physics Electricity & Magnetism Questions 2016

Q8. In electric supply lines in India, which parameter is kept constant?

(A) Voltage
(B) Current
(C) Frequency
(D) Power

Correct Answer: (C) Frequency

Q10. Which one of the following is printed on a commonly used fluorescent tubelight?

(A) 220 K
(B) 273 K
(C) 6500 K
(D) 9000 K

Correct Answer: (C) 6500 K

Q11. Electricians use rubber gloves while working because

(A) Rubber is a good conductor.
(B) Rubber is an insulator.
(C) It is easy to work while wearing gloves.
(D) None of the above.

Correct Answer: (B) Rubber is an insulator.

Q12. The electrical circuits used to get smooth D.C. output from a rectified circuit is called

(A) Amplifier
(B) Filter
(C) Oscillator
(D) Full wave rectifier

Correct Answer: (B) Filter

Q87. The internal resistance of a dry cell is

(A) Equal to that of electrolytic cell
(B) Smaller than that of electrolytic cell
(C) Higher than that of electrolytic cell
(D) Zero

Correct Answer: (B) Smaller than that of electrolytic cell

WBCS Mains Physics Electricity & Magnetism Questions 2015

Q47. Fluorescent tubes are fitted with a choke. The choke coil

(A) Steps up the line voltage
(B) Steps down the line voltage
(C) Reduces the current in the circuit
(D) Chokes low frequency current

Correct Answer: (A) Steps up the line voltage