A power transmission line feeds input power at 2300V to a step down transformer with its primary windings having 4000 turns, giving the output power at 230 V. If the current in the primary of the transformer is 5A, and its efficiency is 90%, the output current would be:

1. 50 A

2. 45 A

3. 25 A

4. 20 A

At a moment (t = 0), when the charge on capacitor C₁ is zero, the switch is closed. If I₀ be the current through inductor at t = 0 , for t > 0                               

1. maximum current through inductor equals I₀/2.    

2. maximum current through inductor equals $\frac{{\mathrm{C}}_1{\mathrm{I}}_0}{{\mathrm{C}}_1+{\mathrm{C}}_2}$

3. maximum charge on ${\mathrm{C}}_1=\frac{{\mathrm{C}}_1{\mathrm{I}}_0\sqrt{{\mathrm{LC}}_2}}{{\mathrm{C}}_1+{\mathrm{C}}_2}$

4. maximum charge on ${\mathrm{C}}_1={\mathrm{C}}_1{\mathrm{I}}_0\sqrt{\frac{\mathrm{L}}{{\mathrm{C}}_1+{\mathrm{C}}_2}}$

A wire of resistance R is connected in series with an inductor of reactance $\mathrm{\omega }$L. Then quality factor of RL circuit is

1.  $\frac{R}{\omega L}$

2.  $\frac{\omega L}{\mathrm{R}}$

3.  $\frac{R}{\sqrt{R^2 + {\omega }^2{L}^2}}$

4.  $\frac{\omega L}{\sqrt{R^2 + {\omega }^2{L}^2}}$

Which of the following combinations should be selected for better tuning of an LCR circuit used for communication?

1.  R = 25 $\Omega$, L = 2.5 H, C = 45 $\mu F$

2.  R = 15 $\Omega$, L = 3.5 H, C = 30 $\mu F$

3.  R = 25 $\Omega$, L = 1.5 H, C = 45 $\mu F$

4.  R = 20 $\Omega$, L = 1.5 H, C = 35 $\mu F$

The core of a transformer is laminated to reduce energy losses due to  

(1) Eddy currents

(2) Hysteresis

(3) Resistance in winding

(4) None of these

A power transformer is used to step up an alternating e.m.f. of 220 V to 11 kV to transmit 4.4 kW of power. If the primary coil has 1000 turns, what is the current rating of the secondary ? Assume 100% efficiency for the transformer 

(1) 4 A

(2) 0.4 A

(3) 0.04 A

(4) 0.2 A

A step-down transformer is connected to main supply 200V to operate a 6V, 30W bulb. The current in primary is 

(1) 3 A

(2) 1.5 A

(3) 0.3 A

(4) 0.15 A

A transformer having efficiency of 90% is working on 200 V and 3 kW power supply. If the current in the secondary coil is 6A, the voltage across the secondary coil and the current in the primary coil respectively are

(1) 300V,15A

(2) 450V,15A

(3) 450V,13.5A

(4) 600V,15A