Chapter 20, Problem 31Q

To determine

To design: A relay to close an electrical switch.

Answer to Problem 31Q

A relay can be designed by using a strong magnetic field of solenoid attracting a piece of iron connected to a circuit carrying a large current.

Explanation of Solution

Introduction:

A solenoid is designed by wrapping coils around an iron bar. When coils are passed with a current then a combination of iron bar and coil i.e. solenoid acts as an electromagnet.

As shown in the figure below, a relay is designed, by wrapping coils around an iron rod works as a combination of a solenoid. This combination is later placed near and pointing towards an end of a piece of iron connected with spring to the large current-carrying circuit. This spring helps to keep the iron away to keep the circuit open. When the relay is activated then all the magnetic domains in the iron bar inside the coils align themselves in a destined direction to maximize the magnetic field. This generates a strong magnetic field that attracts the iron connected with the spring towards it. When it is attracted then circuit closes and allows it to flow through the large current.

  

Conclusion:

Thus, a relay can be designed by using a strong magnetic field of solenoid attracting a piece of iron connected to it and allows it to flow through a large current circuit.