Question

One application of electromagnetism is an electrical switch called a “relay.” These are used in many different kinds of systems that require a high power signal or circuit to be controlled by a small signal, or that require the control circuit to be completely electrically isolated from the controlled circuit. The long-range “action at a distance” magnetic force provides a solution to these issues. The diagram below left shows one possible relay geometry. This would allow, for example, high voltage to be switched between a and b using a relatively small current in the coil. Assume the diagram shows equilibrium when there is no current in the solenoid. Describe what happens, and why, to the magnet, the spring, and points a and b when a current flows through the solenoid. What direction should the current flow? (don’t just guess, explain why) What happens when the current is switched off?

to power supply magnet Ob spring solenoid

Answer 1

Here , the direction of current shows in the solenoid from this direction if you apply right hand thumb rule where curl finger denotes the direction of current and thumb denotes the direction of magnetic field produced by the solenoid .you can see that the magnetic field produced by the solenoid is directed away from the magnet and hence the Bob will remains same at a position .

Current should flow in oppsite direction of given mention direction so that the produced magnetic field will direct towards given magnet and attraction event occur between the magnet and the solenoid and Bob will move from position a to position b and circuit will become close and relay will operate and it will send the signal to the circuit breaker about fault.

If current switch off then no magnetic field produced by the solenoid and no attraction event occur between the magnet and solenoid and relay will not operate even though there is fault on transmission line and relay will not able to send signal about fault to circuit breaker and this fault current will make damage in the system .