Two wires A and B with circular cross-section are made of the same metal and have equal lengths, but the resistance of wire A is five times greater than that of wire B. What is the ratio of the radius of A to that of B?

The ratio of radius of A to that of B is .                                        

Explanation:

The resistance of a wire is given by :

l is length of wire

A is area of cross section

Resistance of wire A is : .......(1)

Resistance of wire B,   .....(2)

As and (given)

From equation (1) and (2) and putting given condition, we get :

Since, . So,

So, the ratio of radius of A to that of B is .

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