JEE Main 2026 Jan 21 Shift 1, Physics Q15: Thermal Expansion

JEE Main2026Jan 21, Shift 1Physics

An aluminium and steel rods having same lengths and cross-sections are joined to make total length of 120 cm at 30°C. The coefficient of linear expansion of aluminium and steel are $24 \times 1 0^{- 6}$ /°C and $1.2 \times 1 0^{- 5}$ /°C, respectively. The length of this composite rod when its temperature is raised to 100°C, is ____ cm.

A
120.20
B
120.15
C
120.03
D
120.06

Solution

Each rod is 60 cm long. Temperature rise $Δ T = 70$ °C. Each rod expands independently and the total final length is the sum:

$L_{f ina l} = 60 (1 + 24 \times 1 0^{- 6} \cdot 70) + 60 (1 + 12 \times 1 0^{- 6} \cdot 70)$

$= 60 (2 + (24 + 12) \times 1 0^{- 6} \cdot 70) = 60 (2 + 0.00252) = 120.15$ cm.

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JEE Main 2026 Jan 21 Shift 1, Physics Q15: Thermal Expansion

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