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JEE Main 20199 AprilEvening Shift
Exam
JEE Main
Year
2019
Date
9 April
Shift
Evening Shift
Subject
Physics
Chapter
Thermal Properties of Matter

JEE Main 2019 · 9 April · Evening Shift · Physics · Thermal Properties of Matter

Two materials having coefficients of thermal conductivity 3K and K...

Two materials having coefficients of thermal conductivity 3KandK3K and K and thickness d and 3d3\text{d} respectively, are joined to form a slab as shown in the figure. The temperatures of the outer surfaces are θ2andθ1{\theta}_{2} and {\theta}_{1} respectively, \left({\theta}_{2} > {\theta}_{1}\right) . The temperature at the interface is

Two materials having coefficients of thermal conductivity 3K and K and thickness d and 3d respectively, are joined to

Options

  1. Aθ2+θ12\dfrac{{\theta}_{2} + {\theta}_{1}}{2}
  2. Bθ16+5θ26\dfrac{{\theta}_{1}}{6} + \dfrac{5{\theta}_{2}}{6}
  3. Cθ13+2θ23\dfrac{{\theta}_{1}}{3} + \dfrac{2{\theta}_{2}}{3}
  4. Dθ110+9θ210\dfrac{{\theta}_{1}}{10} + \dfrac{9{\theta}_{2}}{10}

Correct answer

D. θ110+9θ210\dfrac{{\theta}_{1}}{10} + \dfrac{9{\theta}_{2}}{10}

Step-by-step solution

Two materials having coefficients of thermal conductivity 3K and K and thickness d and 3d respectively, are joined to

Let the temperature of the junction T°CT ° C .

Rate of heat flow in Rod 11 = rate of heat flow in Rod 22

3kAd(θ2−T)=kA3d(T−θ1)\dfrac{3kA}{d}\left({\theta}_{2} - T\right) = \dfrac{kA}{3d}\left(T - {\theta}_{1}\right)

⇒9(θ2−T)=(T−θ1)⇒ 9\left({\theta}_{2} - T\right) = \left(T - {\theta}_{1}\right)

⇒10T=9θ2+θ1⇒ 10T = 9{\theta}_{2} + {\theta}_{1}

⇒T=9θ2+θ110=θ110+9θ210⇒ T = \dfrac{9{\theta}_{2} + {\theta}_{1}}{10} = \dfrac{{\theta}_{1}}{10} + \dfrac{9{\theta}_{2}}{10}

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