b
ઊર્જા \( = \frac{1}{2} \times \) પ્રતિબળ \(\times\) વિકૃતિ \(\times\) \(volume\) \( = \frac{1}{2} \times \frac{F}{A}\) \(\times\) \(strain \)\(\times\)\( AL\) \( = \frac{1}{2} \times F \times strain \times L\)

\((A)\) \(U = \frac{1}{2} \times 10 \times {10^{ - 3}} \times L = 5 \times {10^{ - 3}}L\);

\((B)\) \(U = \frac{1}{2} \times 15 \times {10^{ - 3}} \times L = 7.5 \times {10^{ - 3}}L\)

\((C)\) \(U = \frac{1}{2} \times 10 \times {10^{ - 4}} \times L = 0.5 \times {10^{ - 3}}L\);

\((D)\) \(U = \frac{1}{2} \times 5 \times {10^{ - 3}} = 2.5 \times {10^{ - 3}}L\)