Exams › JEE Main › Physics

A copper bar 75 cm long is joined end to end with a steel bar 125 cm long; both have circular cross-section of diameter 2 cm and their curved surfaces are insulated. The free copper end is held at 100 C and the free steel end at 0 C. Thermal conductivity of copper = 386 J s⁻¹ m⁻¹ C⁻¹ and of steel = 46 J s⁻¹ m⁻¹ C⁻¹. Which statement is correct?

1. Temperature of the junction is 7 C
2. Temperature of the junction is 93 C
3. Amount of heat transmitted across the junction per unit time is 1.07 J s⁻¹
4. Amount of heat transmitted across the junction per unit time is 2.14 J s⁻¹

Correct answer: Temperature of the junction is 93 C

Solution

Equating the steady-state heat currents gives T approximately 93 C (and the corresponding heat current is about 1.07 J/s); the junction temperature is 93 C.

Related JEE Main Physics questions

• A cube initially at 0°C is subjected to the same external pressure P on all its faces, causing it to be compressed. How much must its temperature be increased so that the cube regains its original size? The bulk modulus of the cube material is B and its coefficient of linear expansion is α.
• If λm represents the wavelength at which a black body emits radiation most strongly at temperature T K, then which relation is true?
• Which of the following statements about heat transfer is/are incorrect?
• A composite wall consists of two slabs, A and B, of equal thickness but made of different materials. Their thermal conductivities satisfy K_A = 3K_B. If the total temperature difference across the wall is 20°C, then in steady thermal equilibrium:
• An evacuated bulb contains a filament that is 10 cm long and 0.2 mm in diameter. If its emissivity is 0.2, determine the radiant power emitted by the filament at 2000 K. Take σ = 5.67 × 10⁻⁸ W/m² K⁴.
• A rectangular solid is raised in temperature from 0°C to 100°C. If its length increases by 0.10% over this interval, what is the corresponding percentage increase in its volume?

⚔️ Practice JEE Main Physics free + battle 1v1 →