15.1: A transformer is needed to convert a mains 240 V supply into a 12 V supply. If there are 2000 turns on the primary coil, then find the number of turns on the secondary coil. Ans. (100)


15.2: A step-up transformer has a turn ratios of 1 : 100. An alternating supply of 20 V is 15 .5 connected across the primary coil. What is the secondary voltage? Ans. (2000 V)

15.3: A step-down transformer has a turns ratio of 100 : 1. An ac voltage of amplitude 170 V is applied to the primary. If the current in the primary is 1.0 mA, what is the current in the secondary? Ans. (0.1A)


15.4: A transformer, designed to convert the voltage from 240 V a.c. mains to 12 V, has 4000 turns on the primary coil. How many turns should be on the secondary coil? If the transformer were 100% efficient, what current would flow through the primary coil when the current in the secondary coil was 0.4 A? Ans. (200, 0.02A)


15.5: A power station generates 500 MW of electrical power which is fed to a transmission line. What current would flow in the transmission line if the input voltage is 250 kV? Ans. (2 x 103 A)