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

The primary and secondary coils of a transformer have 50 and 1500 turns respectively. If the magnetic flux $\varphi$ linked with the primary coils is given by \(\phi=\phi_0+4t\), where \(\phi\) is in webers, t is time in seconds, and \(\phi_0\) is a constant, the output voltage across the secondary coil is:

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

The primary winding of a transformer has 500 turns whereas its secondary has 5000 turns. The primary is connected to an ac supply of 20 V, 50 Hz. What will be the output of the secondary transformer?

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

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

1. 3.6A                                        2. 2.8A

3. 2.5A                                        4. 5.0A

In an ideal transformer, the voltage and the current in the primary are 200 volt and 2 amp. respectively. If the voltage in the secondary is 2000 volt. Then value of current in the secondary will be – 

1.  0.2 amp.                     

2.  2 amp. 

3.  10 amp.                       

4.  20 amp.