Alternating Current

A 220 V input is supplied to a transformer. The output circuit draws a current 2.0 A at 440 V. If the efficiency of the transformer is 80%, the current drawn by the primary windings of the transformer is 

• 3.6 A

• 2.8 A

• 2.5 A

• 2.5 A

The two ends f a rod of length L and a uniform cross -sectional area A are kept at two temperatures T₁ and T₂ (T₂ > T₁) .The rate of heat transfer, dQ/dt, through the rod in steady state is given by

A galvanometer having a coil resistance of 60 Ω shows full-scale deflection when a current of 1.0 A passes through it. It can be converted into an ammeter to read currents up to 5.0 A by

• putting in parallel a resistance of 240 Ω

• putting in series a resistance of 15 Ω

• putting in series a resistance of 240 Ω

• putting in series a resistance of 240 Ω

In an AC circuit, the emf (e) and the current (i) at any instant are given respectively by

e = E₀ sin ωt
i = I_o sin (ωt -Φ)

The average power in the circuit over one cycle of AC is

In the circuit shown, the current through the 4 Ω resistor is 1 A when the points P and M are connected to a DC voltage source. The potential difference between the point M and N is 

• 1.5 V

• 1.0 V

• 0.5 V

• 0.5 V

The primary and secondary coil of a transformer have 50 and 1500 turns respectively. If the magnetic flux Φ linked with the primary coil is given Φ = Φ_o +4t, where Φ is in weber, t is time is second and Φ_o is a constant the output voltage across the secondary coil is:

• 90 V

• 120 V

• 220 V

• 220 V

A charged particle (charge q ) is moving n a circle of radius R with uniform speed v. The associated magnetic moment μ is given by:

• qvR/2

• qVR²

• qVR²/2

• qVR²/2

A common emitter amplifier has a voltage gain of 50, an input impedance of 100 Ω and an output impedance of 200 Ω. The power gain of the amplifier is:

• 500

• 1000

• 1250

• 1250

The core of a transformer is laminated because

• energy losses due to eddy currents may be minimised

• the weight of the transformer may be reduced

• rusting of the core may be prevented

• rusting of the core may be prevented

A coil of inductive reactance 31 Ω has a resistance of 8Ω. It is placed in series with a condenser of capacitative reactance 25Ω. The combination is connected to an a.c. soruce of 110 V. The power factor of the circuit is

• 0.56

• 0.64

• 0.80

• 0.80