Q. No.The core of a transformer is laminated because:
| 1. | Energy losses due to eddy currents may be minimized |
| 2. | The weight of the transformer may be reduced |
| 3. | Rusting of the core may be prevented |
| 4. | Ratio of voltage in primary and secondary may be increased |
Turn ratio of a step-up transformer is \(1: 25\). If current in load coil is \(2~\text{A}\), then the current in primary coil will be:
| 1. | \(25~\text{A}\) | 2. | \(50~\text{A}\) |
| 3. | \(0.25~\text{A}\) | 4. | \(0.5~\text{A}\) |
The primary and secondary coils of a transformer have 50 and 1500 turns respectively. If the magnetic flux 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:
| 1. | 120 V | 2. | 220 V |
| 3. | 30 V | 4. | 90 V |
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?
| 1. | 200 V, 50 Hz |
| 2. | 2 V, 50 Hz |
| 3. | 200 V, 500 Hz |
| 4. | 2 V, 5 Hz |
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 |
In a step-up transformer, the turn ratio is 1: 20. The resistance of 100 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
When a step-down transformer is connected to a 2400 volt line, the output load receives 80 amps of current. The ratio of the turns in the primary and secondary coils is 20:1. If transformer efficiency is 100%, then the current flowing in the primary coil will be:
| 1. | 1600 A | 2. | 20 A |
| 3. | 4 A | 4. | 1.5 A |
In the transformer shown in the figure, the ratio of the number of turns of the primary to the secondary is N1/N2=1/50. If a voltage source of 10 V is connected across the primary, then the induced current through the load of 10 kΩ in the secondary is:
1. \(\frac{1}{20}~A\)
2. zero
3. \(\frac{1}{10}~A\)
4. \(\frac{1}{5}~A\)
1. 3.6 A
2. 2.8 A
3. 2.5 A
4. 5.0 A
A transformer has an efficiency of 90% when working on a 200 V and 3 kW power supply. If the current in the secondary coil is 6 A, the voltage across the secondary coil and the current in the primary coil, respectively, are:
1. 300 V, 15 A
2. 450 V, 15 A
3. 450 V, 13.5 A
4. 600 V, 15 A
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