Question

One morning an old man walked bare-foot to replace the fuse wire in kit kat fitted with power supply mains for his house. Suddenly he screamed and collapsed on the floor. His wife cried loudly for help. His neighbour's son Anil heard the cries and rushed to the place with shoes on. He took a wooden baton and used it to switch off the main supply.
Answer the following questions :
(i) What is the voltage and frequency of mains supply in India?
(ii) These days most of the electrical devices we use require a.c. voltage. Why?
(iii) Can a transformer be used to step up d.c. voltage?
(iv) Write two qualities displayed by Anil by his action.

Answer 1

(i)

The voltage of mains supply in India is 220 V rms and frequency is 50 Hz.

(ii)

Since most of the devices are used on mains supply which supplies a.c. voltage, they are designed to be used with a.c. voltage.

(iii)

Transformer can only step-up and step-down a.c. voltages as transformer consists of inductors. The secondary of transformer induces voltage only when a changing flux is passed through it according to:

$e=-\frac{d\varphi }{dt}$

For d.c. voltages, $\varphi$ is constant and hence, secondary coil does not induce any voltage for d.c.

(iv)

The two qualities displayed by Anil in the action are:

1. Preventing himself being the earthing conductor by putting on wooden shoes.Anil is caring as well as intelligent and helpful also.

2. Switching off the mains supply to prevent the old man to act as an earthing conductor.