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) rate of change of linked... 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) = 60 x [(1.5 - 1)/0.1] = 300 mV The induced... 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 self-inductor, E = (1/2)Li2 = (1/2) x 200 x 10-3... 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... View Article
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 = 0.5 A Voltage across the primary, Vp... 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 transformer is (Np/Ns) = (Vp/Vs)... 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 = Is/Ip (50/200) = Is/1 ⇒ Is = 1 A... 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, ⇒ Ip = (25/1) x 2 = 50 A... View Article
The induction furnace is based on the heating effect of 1) electric field 2) eddy current 3) magnetic field 4) gravitational field Answer: 2) eddy current Solution: Eddy current has... View Article
For a large industrial city with many load variations, the DC generator should be 1) series 2) shunt-wound 3) mixed wound 4) Any of the above Answer: 3) mixed wound Solution: The DC generator must be mixed wound to... View Article
The core of a transformer is laminated to reduce 1) flux leakage 2) output power 3) hysteresis 4) copper loss 5) eddy current Answer: 5) eddy current Solution: Eddy currents are... View Article
A transformer works on the principle of 1) magnetic effect of the electrical current 2) mutual induction 3) electrical inertia 4) self-induction Answer: 2) mutual induction... 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 the primary winding, Np= 1000 turns 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 Answer: 3) 1.2 x 10-6 N Solution: The average force by light on the... View Article
In the microwave oven, we use electromagnetic oscillators which produce electromagnetic waves in the wavelength range 1) 1mm to 10m 2) 0.7 μm to 1mm 3) 0.1 m to 1mm 4) 0.1 μm to 0.7 μm Answer: 3) 0.1 m to 1mm Solution: In the microwave oven,... View Article
Our eyes respond to wavelength ranging from 1) 400nm to 700nm 2) -∞ to +∞ 3) 1mm to 700nm 4) 700nm to 800nm Answer: 1) 400nm to 700nm Solution: Our eyes respond to... View Article
What is the ratio of velocities of light rays of wavelengths 4000oA and 8000oA in vacuum? 1) 1 : 2 2) 1 : 1 3) 2 : 1 4) cannot be determined Answer:2) 1 : 1 Solution: The velocity of all light rays is the same. Hence, the ratio... View Article
Unit of energy density of electromagnetic wave is _____________ 1) Jm-3 2) Jm-2 3) Wm-2 4) None of these Answer: 1) Jm-3 Solution: Energy density = Energy/Volume = J/m3 = Jm-3... View Article
The frequency of electromagnetic wave having wavelength 25mm is ____________ Hz 1) 1.2 x 1010 2) 7.5 x 105 3) 1.2 x 108 4) 7.5 x 106 Answer: 1) 1.2 x 1010Hz Solution: Frequency= velocity/wavelength f =c/λ... View Article
Which of the following electromagnetic waves is used in telecommunication? 1) radio waves 2) visible radiations 3) ultraviolet rays 4) microwaves Answer: 4) microwaves Solution: Microwaves are used... View Article
