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

For the circuit shown in figure, the voltage across 4 Ω resistance is

• 1 V

• 2 V

• 4 V

• 5 V

A LED has a voltage drop of 2V across it and passes a current of 10 mA. When it operates with a 6V battery through a limiting resistor R. The value of R is

• 40 kΩ

• 200 Ω

• 4 kΩ

• 400 Ω

A series R-L-C circuit driven with E_rms = 100V and frequency f_d = 50 Hz is shown below.

What new capacitance should be connected to maximize the average power, if other parameters of the circuit are not changed ?

• 41.6 µF

• 33.5 µF

• 39.8 µF

• 31.3 µF

An L-C-R series circuit with 100 Ω resistance is connected to an AC source of 200 V and angular frequency 300 rad s^-1 . When only the capacitance is removed, the current lags behind the voltage by 60°. When only the inductance is removed, the current leads the voltage by 60°. The average power dissipated in this L-C-R circuit is

• 0

• 400 W

• 200 W

• 800 W

Given,

R₁ = 10 Ω, C₁ = 2µF, R₂ = 20 and C₂ =  4F

The time constants (in µs) for the circuits I, II, III are respectively.

• 18, 18/9, 4

• 4, 8/9, 18

• 18, 4, 8/9

• 8/9, 18, 4