Question

Electric door bell employs
A. permanent magnet
B. electromagnet
C. thermistor
D. electric bulb

Answer 1

Hint: Here we have a one word problem. As a first step one could give the basic working principle of an electric door bell. Then you could also explain the working of this device. By now you might have found the component that is used in an electric bell among the given ones.

Complete step-by-step solution:
In the question we are asked to find the component among the given options that is used for making an electric door bell. You may be familiar with this object that is an electric bell that is used as a doorbell in most households. The basic mechanism behind this device is based on electromagnetism. This device basically consists of an electromagnet that works as a magnet on applying electric current into it. On pressing the switch, the circuit is complete which results in the coil producing magnetic field and thereby functioning as a magnet.
Another component of the device which is a hammer made of metal attached to a spring would get attracted to this magnet. At the same time spring force acts in the opposite direction. So, this is repeated and hence the bell rings again and again.
Therefore, we could conclude that the electric bell employs electromagnet. Hence, option B is correct.

Note: So, basically it is the hammer hitting the electromagnet and the spring force pulling it back to its equilibrium position that is responsible for ringing the bell. But another condition to be satisfied here is that the bell should work on applying electricity and only electromagnets work accordingly.