Question

In a grid iron pendulum , there are 3 iron rods and 4 brass rods , Length of each brass rod is 50 cm . $\alpha$ of iron is $12 \times 10^{-6} \,/^{\circ} C$ and $\alpha$ of brass is $18 \times 10^{-6}\,/^{\circ} C$ . Length of each iron rod is

• A. 50 cm
• B. 100cm
• C. 120 cm
• D. 60 cm

Answer 1

Answer: (B)

100cm

Answer 2

Total change in lengths of the brass and iron rods must be same with equal change in temperature. Hence $3 l _{\text {iron }} \alpha_{\text {iron }} \Delta \theta=4 l _{\text {brass }} \alpha_{\text {brass }} \Delta \theta$ $\Longrightarrow l _{\text {iron }}=2 l _{\text {brass }}=100 cm$