Question

What's the function of Plug key ?

Answer 1

A plug key is just like a switch. It has a small metal rod and a base in which wires are connected. When the circuit is to be switched on, the metal rod is inserted in the base. 

A rheostat helps in adjusting resistance. It is used in labs in the experiment of Ohm's law. 
For experiment, we need different readings. For different readings, we need different resistance (Since the voltage is constant) 
So for different resistances, rheostat is used. 
(You cannot look for different wires for your desired resistance. It will just be too tedious.)


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