Question:

A copper rod of 88 cm and an aluminium rod of unknown length have their increase in length independent of increase in temperature. The length of aluminium rod is :(αCu=1.7×10⁻⁵K⁻¹;and αAl=2.2×10⁻⁵K⁻¹)

6.8cm

113.9cm

88cm

68cm

Correct option is D. 68cm
We know,
αCuLCu = αAlLA
⇒1.7×10⁻⁵ × 88cm = 2.2×10⁻⁵ × LAl
⇒LAl = (1.7 × 88) / 2.2 = 68cm