Latest Posts

A transformer of efficiency 90% draws an input power of 4 kW. An electrical appliance connected across the secondary draws a current of 6 A. The impedance of the device is

1) 60 Ω 2) 50 Ω 3) 80 Ω 4) 100 Ω 5) 120 Ω Answer: 4) 100 Ω Solution: η... View Article

An electric motor runs a DC source of emf 200 V and draws a current of 10 A. If the efficiency is 40%, then the resistance of the armature is

1) 5 Ω 2) 12 Ω 3) 120 Ω 4) 160 Ω Answer: 2) 12 Ω Solution: Input power = VI... View Article

Energy associated with a moving charge is due to

1) electric field 2) magnetic field 3) Both (a) and (b) 4) None of these Answer: 1) electric field Solution: The... View Article

In a coil when current changes from 10 A to 2 A in time 0.1 s, induced emf is 3.28 V. What is self-inductance of the coil?

1) 4H 2) 0.4 H 3) 0.04 H 4) 5 H Answer: 3) 0.04 H Solution: Induced emf = L x... View Article

If coil is open, then L and R become

1) ∞ and 0 2) 0 and ∞ 3) ∞ and ∞ 4) 0 and 0 Answer: 2) 0 and ∞... View Article

A solenoid of inductance 2 H carries a current 1 A. What is the magnetic energy stored in a solenoid?

1) 2 J 2) 1 J 3) 4 J 4) 5 J Answer:2) 1 J Solution: Magnetic energy stored, Um... View Article

Induced emf in the coil depends upon

1) conductivity of coil 2) amount of flux 3) rate of change of linked flux 4) resistance of coil Answer: 3)... View Article

In 0.1s, the current in a coil increases from 1 A to 1.5 A. If the inductance of the coil is 60 mH, then induced current in external resistance of 3 Ω will be

1) 1 A 2) 0.5 A 3) 0.2 A 4) 0.1 A Answer: 4) 0.1 A Solution: Induced emf is, L(di/dt)... View Article

Energy required to establish a current of 4 A in a coil of self inductance L= 200 mH is

1) 0.16 J 2) 0.18 J 3) 0.40 J 4) 1.6 J Answer: 4) 1.6 J Solution: Energy stored in a... View Article

Quantity that remains unchanged in a transformer is

1) voltage 2) current 3) frequency 4) None of these Answer: 3) frequency Solution: Frequency remains unchanged in a transformer

A transformer is used to light a 100 W and 110 V lamp from a 220 V mains. If the main current is 0.5 A, the efficiency of a transformer is approximately

1) 30% 2) 50% 3) 90% 4) 10% Answer: 3) 90% Solution: Power = 100 W Current in the primary, Ip... View Article

A transformer rated at 10 kW is used to connect a 5 kV transmission line to a 240 V circuit. The ratio of turns in the windings of the transformer is

1) 5 2) 20.8 3) 104 4) 40 Answer: 2) 20.8 Solution: The ratio of turns in the windings of the... View Article

The number of turns in primary and secondary coils of a transformer is 50 and 200, respectively. If the current in the primary coil is 4 A, then the current in the secondary coil is

1) 1 A 2) 2 A 3) 4 A 4) 5 A Answer: 1) 1 A Solution: In a transformer Np/Ns... View Article

Turn ratio is 1.25. The step-up transformer operates at 230 V and the current through secondary is 2 A. Then, current in the primary is

1) 25 A 2) 100 A 3) 50 A 4) 20 A Answer:3) 50 A Solution: in an ideal transformer,... View Article

A step-down transformer has 50 turns on secondary and 1000 turns on the primary winding. If a transformer is connected to 220 V and 1 A AC source, what is the output current of the transformer?

1) 1/20 A 2) 20 A 3) 100 A 4) 2 A Answer: 2) 20 A Solution: Number of turns in... View Article

Light with an energy flux of 18 w/m³ or Wm^–3 falls on a non-reflecting surface at normal to the surface. If the surface has an area of 20m². The average force exerted on the surface during 30 minutes is ______________

1) 6.48 x 105 N 2) 3.60 x 102 N 3) 1.2 x 10-6 N 4) 2.16 x 10-3 N... View Article

«
1
…
936
937
938
939
940
…
5,472
»