Alternating Current

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

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

When a given coil of ohmic resistance 100 Ω and inductive reactance 100$\sqrt{3}$ Ω is connected to a 200 V DC source, the current flows in the circuit is

• 1 A

• 1.5 A

• 2 A

• $100\sqrt{3}$ Ω

The ratio of inductive reactance to capacitive reactance in an AC circuit will be

• ω LC

• ω² L

• zero

• ω² LC

In a step up transformer, the turns ratio of field is primary and secondary is 1 : 4. A  leclanche cell of emf 1.5 V is connected across the primary. The voltage developed across the secondary will be

• 3 V

• 6 V

• 1 V

• zero

When an AC source of emf e = E₀ sin (100t) is connected across a circuit, the phase difference between the emf e and the current i in the circuit is observed to be $\mathrm{\pi }$/4, as shown in the diagram. If the circuit consists possibly only of R-C or R-L or L-C is series, find the relationship between the two elements.

• R = 1 kΩ , C = 10 µF

• R = 1 kΩ , C = 1 µF

• R = 1 kΩ , L = 10 H

• R = 1 kΩ , L = 1 H