EXERCISE 8

1. A transformer has 200 turns in the primary, 50 turns in the secondary, and 120 volts applied to the primary (Ep). What is the voltage across the secondary (Es)?

2. There are 400 turns of wire in an iron-core coil. If this coil is to be used as the primary of a transformer, how many turns must be wound on the coil to form the secondary winding of the transformer to have a secondary voltage of one volt if the primary voltage is five volts?

3. A transformer has a 6:1 voltage ratio. Find the current in the secondary if the current in the primary is 200 milliamperes.

4. A transformer with a turns ratio of 1:12 has 3 amperes of current in the secondary. What is the value of current in the primary?

5. If the input power to a transformer is 650 watts and the output power is 610 watts, what is the efficiency?

6. A transformer has 500 turns on the primary and 1500 turns on the secondary. If 45 volts are applied to the primary, what is the voltage developed across the secondary?

7. A transformer has a turns ratio of 7:1. If 5 volts is developed across the secondary, what is the voltage applied to the primary?

8. A transformer has 60 volts applied to its primary and 420 volts appearing across its secondary. If there are 800 turns on the primary, what is the number of turns in the secondary?

9. A transformer with a turns ratio of 1:3 has what current ratio?

10. A transformer has a turns ratio of 5:1 and a current of 5 amperes flowing in the secondary. What is the current flowing in the primary?

11. The input power to a transformer is 1,000 watts and the output power is 500 watts. What is the efficiency of the transformer, expressed as a percentage?

12. What ratio of transformer is required to make a load of resistance 30 Ω to have a resistance of 270 Ω?

13. Determine the optimum value of load resistance for maximum power transfer if the load is connected to an amplifier of output resistance 147 Ω through a transformer with a turns ratio of 7:2.

14. A transformer having a turns ratio of 8:1 supplies a load of resistance 50 Ω. Determine the equivalent input resistance of the transformer.

15. A single-phase, 240 V/2 880 V ideal transformer is supplied from a 240 V source through a cable of resistance 3 Ω. If the load across the secondary winding is 720 Ω determine (a) the primary current flowing and (b) the power dissipated in the load resistance.

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