A step–down transformer transforms a supply line voltage of 2200 volt into 220 volt. The primary coil has 5000 turns. The efficiency and power transmitted by the transformer are 90% and 8 kilowatts respectively. How many turns are there in the secondary one?

1.	5000	2.	50
3.	500	4.	5

Match List I (expression for current) with List II (RMS value of current) and select the correct answer.

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:

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?

If R and L are resistance and inductance of a choke coil and f is the frequency of current through it, then the average power of the choke coil is proportional to:
1.  \(R ~\)
2.  \(\frac{1}{f^2}\)
3.  \(\frac{1}{L^2}\)
4.  All of these

In the network shown below what is the reading of the a.c voltmeter?
                  
1. Zero

2. 100 V

3. 200 V

4. 500 V

The power factor of the given circuit is:
           

The power factor of a series LCR circuit in resonance condition is:

$1.$ $Zero$ $$
$2.$ $\frac{1}{2}$
$3.$ $\frac{1}{\sqrt{2}}$
$4.$ $1$

What is the instantaneous power of a resistor having resistance R across an ac supply of E=E₀sin ωt?

$1.$ $\frac{{E_0}^2}{R}{\sin }^2$ $\omega t$
$2.$ $\frac{{E_0}^2}{R}{\cos }^2$ $\omega t$
$3.$ $\frac{{E_0}^2}{R}$
$4.$ $zero$ $$

In a step-up transformer, the turn ratio is 1: 20. The resistance of 100 $\Omega$ connected across the secondary is drawing a current of 2 A. What are the primary voltage and current respectively?

1. 100 V, 0.5 A

2. 200 V, 10 A

3. 10 V, 40 A

4. 10 v, 20 A