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JEE Main202621 January 2026Morning ShiftPhysicsThermal Properties of MatterActual

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 10⁻⁶ / ^ C and 1.2 10⁻⁵ / ^ C , respectively. The length of this composite rod when its temperature is raised to 100^ C , is _ _ _ _ cm.

Options

  1. A120.20
  2. B120.15
  3. C120.06
  4. D120.03

Correct answer

B. 120.15

Step-by-step solution

Total length at 30°C = 120 cm, each rod = 60 cm _ Al = 24 10⁻⁶ /°C, _ Steel = 1.2 10⁻⁵ /°C T = 100 - 30 = 70 °C L_ Al = 60 24 10⁻⁶ 70 = 0.1008 cm L_ Steel = 60 1.2 10⁻⁵ 70 = 0.0504 cm Total expansion = 0.1008 + 0.0504 = 0.1512 cm Final length = 120 + 0.1512 = 120.15 cm

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