Question

3. Consider a wire of length L and area of ​​cross-section A. We cut up the wire into 4 equal parts (we mean equal lengths) to get wires W1, W2, W3 and W4. Now, each wire W; (where i = 1,2, 3, 4) is stretched to i times its length. Then we put the larger three resistances in parallel and combine this in series with the smallest resistance. If the effective resistance is Re = aR / b, where R is the resistance of the original wire and a, b are positive integers with (a, b) = 1, then a - b is:​

Answer 1

Answer:

Work done is equal to the potential energy stored in the wire.

∴       W=U=21×Stress×Strain×Volume

OR         W=21×Y(Strain)2×Volume                    .............(1)               (Strain=Y×Strain)

   Strain=Lx            and    Volume=AL

∴    W=21×Y×L2x2×AL                ⟹W=2LYx2A