TOPIC 5 ELECTRICITY CHAPTER 28 EXERCISE 28C CONTINUED
5. A step-up transformer operates with a 100 V supply and supplies an output with 3 A. If the ratio of primary to secondary windings is 1:30, determine the secondary voltage, primary current and power output, assuming 100% effi ciency.
6. A steady current in a 500-turn coil causes a fl ux of 2 × 10−3 Wb to pass through the ends of the coil. Calculate the average induced back emf, when the circuit is switched off and the fl ux falls to zero in 0.2 s.
7. If a coil of wire of resistance 200 Ω has a steady d.c. voltage of 10 V across it, what d.c. current is produced? If the same coil is now connected to a 10 V a.c. supply, what will happen?
8. A circuit is built so as to consist of a switch, a d.c. supply, an inductor coil and a bulb. What will happen if:
(i) the switch is closed? (ii) the switch is opened again?
(iii) the d.c. supply is replaced with an a.c. supply?
(iv) the inductor coil has a soft iron core placed inside it?
