31.

A galvanometer has a resistance of 30 Q. It gives full scale deflection with a current of 2mA. Calculate, the value of the resistance needed to convert it into an ammeter of range 0 − 0.3 A. The value of the resistance needed to convert galvanometer into ammeter

• 0.2 Ω

• 0.3 Ω

• 0.4 Ω

• 0.52 Ω

The given circuit diagram shows a series L-C-R circuit connected to a variable frequency 230 V, source: L =5.0 H, C = 80 µF, R = 40 Ω

The frequency and impedance of the circuit at the resonating frequency are

• 50 rad/s and 5.75 A

• 1000 rad/s and 3 A

• 10 rad/s and 2 A

• 20 rad/s and 4 A

The instantaneous current and voltage of an AC circuit are given by I= 10 sin 300t A and V  = 200 sin 300t V. The power dissipation in the circuit is

• 500 W

• 2000 W

• 1000 W

• 100 W

In a series L-C-R circuit, the voltages across an inductor, a capacitor and a resistor are 30V, 30V and 60 V respectively. The phase difference between the applied voltage and the current in the circuit is

• O°

• 90°

• 30°

• 60°

An AC source, of voltage V =V_m sin ωt, is applied across a series RC circuit in which the capacitive impedance is 'a' times the resistance in the circuit. The value of the power factor of the circuit is

• O

• $1/\sqrt{1 + {\mathrm{a}}^2}$

• $\sqrt{1 + {\mathrm{a}}^2}$

• None of these

Current in a circuit falls steadily from 2.0 A to 0.0 A in 10 ms. If an average emf of 200 V is induced, then the self-inductance of the circuit is

• 1 H

• 2 H

• 1/2 H

• 2 H

A rectangular coil of area A, having number of turns N is rotated at f revolutions per second in a uniform magnetic field B. The maximum emf induced in the coil is

• $2 \mathrm{\pi }$fNB

• 2fNBA

• $2 \mathrm{\pi }$fBA

• $2 \mathrm{\pi }$fNBA

The polarity of the capacitor in the situation described by Fig.

• Plate A and plate B both positive

• Plate A negative and plate B positive

• Plate A positive and plate B negative

• Plate A and plate B both negative

A step down transformer operated on a 2.5 kV line. It supplies a load with 20 A. The ratio of the primary winding to the secondary is 10 : 1. If the transformer is 90% efficient, the power output is

• 4.5 X 10⁴ W

• 4.5 × 10² W

• 6 x 10⁴ W

• 6 X 10⁴ w

A step down transformer operated on a 2.5 kV line. It supplies a load with 20 A. The ratio of the primary winding to the secondary is 10 : 1. If the transformer is 90% efficient, the voltage in the secondary is

• 225 V

• 550 V

• 250 V

• 200 V