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Two rods, A and B, of different materials having the same cross-sectional area are welded together as shown in the figure. Their thermal conductivities are ${K}_{1}$ and ${K}_{2}$. The thermal conductivity of the composite rod will be:

1. $\frac{{K}_{1}+{K}_{2}}{2}$

2. $\frac{3\left({K}_{1}+{K}_{2}\right)}{2}$

3. ${K}_{1}+{K}_{2}$

4. $2\left({K}_{1}+{K}_{2}\right)$

Subtopic: Conduction |

78%

From NCERT

NEET - 2017

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A spherical black body with a radius of 12 cm radiates 450-watt power at 500 K. If the radius were halved and the temperature doubled, the power radiated in watts would be:

1. | 225 | 2. | 450 |

3. | 1000 | 4. | 1800 |

Subtopic: Stefan-Boltzmann Law |

74%

From NCERT

NEET - 2017

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The coefficients of linear expansion of brass and steel rods are α_{1} and α_{2}, lengths of brass and steel rods are l_{1} and l_{2} respectively. If (l_{2} - l_{1}) is maintained the same at all temperatures, Which one of the following relations holds good?

1. α_{1}l_{2}^{2} = α_{2}l_{1}^{2}

2. α_{1}^{2}l_{2 }= α_{2}^{2}l_{1}

3. α_{1}l_{1 }= α_{2}l_{2}

4. α_{1}l_{2 }= α_{2}l_{1}

Subtopic: Thermal Expansion |

83%

From NCERT

NEET - 2016

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A piece of ice falls from a height \(h\) so that it melts completely. Only one-quarter of the heat produced is absorbed by the ice, and all energy of ice gets converted into heat during its fall. The value of \(h\) is: (Latent heat of ice is \(3.4\times10^5\) J/kg and \(g=10\) N/kg)

1. | \(544\) km | 2. | \(136\) km |

3. | \(68\) km | 4. | \(34\) km |

Subtopic: Calorimetry |

76%

From NCERT

NEET - 2016

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The two ends of a metal rod are maintained at temperatures \(100^{\circ}\mathrm{C}\) and \(110^{\circ}\mathrm{C}\). The rate of heat flow in the rod is found to be 4.0 J/s. If the ends are maintained at temperatures \(200^{\circ}\mathrm{C}\) and \(210^{\circ}\mathrm{C}\), the rate of heat flow will be:

1. 44.0 J/s

2. 16.8 J/s

3. 8.0 J/s

4. 4.0 J/s

Subtopic: Conduction |

87%

From NCERT

NEET - 2015

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A certain quantity of water cools from \(70^{\circ}\mathrm{C}\) to \(60^{\circ}\mathrm{C}\) in the first 5 minutes and to \(54^{\circ}\mathrm{C}\) in the next 5 minutes.

The temperature of the surroundings will be:

1. | \(45^{\circ}\mathrm{C}\) | 2. | \(20^{\circ}\mathrm{C}\) |

3. | \(42^{\circ}\mathrm{C}\) | 4. | \(10^{\circ}\mathrm{C}\) |

Subtopic: Newton's Law of Cooling |

77%

From NCERT

NEET - 2014

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The temperature of a wire of length 1 *meter* and an area of cross-section 1cm^{2} is increased from \(0^{\circ} \mathrm {C}\) to \(100^{\circ} \mathrm {C}\). If the rod is not allowed to increase in length, the force required will be: \((\alpha = 10^{-5}/ ^{\circ} \mathrm {C} ~\text{and} ~Y = 10^{11} ~\text{N/m}^2)\)

1. | \(10^3 \mathrm{~N} \) | 2. | \(10^4 \mathrm{~N} \) |

3. | \(10^5 \mathrm{~N} \) | 4. | \(10^9 \mathrm{~N}\) |

Subtopic: Thermal Stress |

81%

From NCERT

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A metal bar of length *\(L\)* and area of cross-section *\(A\) i*s clamped between two rigid supports. For the material of the rod, its Young’s modulus is *\(Y\)* and the coefficient of linear expansion is \(\alpha\). If the temperature of the rod is increased by \(\Delta t^{\circ} \mathrm{C}\), the force exerted by the rod on the supports will be:

1. \(YAL\Delta t\)

2. \(YA\alpha\Delta t\)

3. \(\frac{YL\alpha\Delta t}{A}\)

4. \(Y\alpha AL\Delta t\)

Subtopic: Thermal Stress |

81%

From NCERT

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When two ends of a rod wrapped with cotton are maintained at different temperatures and, after some time, every point of the rod attains a constant temperature, then:

1. | Conduction of heat at different points of the rod stops because the temperature is not increasing |

2. | The rod is a bad conductor of heat |

3. | Heat is being radiated from each point of the rod |

4. | Each point of the rod is giving heat to its neighbour at the same rate at which it is receiving heat |

Subtopic: Conduction |

75%

From NCERT

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Mud houses are cooler in the summer and warmer in the winter because:

1. | the mud is a superconductor of heat. |

2. | the mud is a good conductor of heat. |

3. | the mud is a bad conductor of heat. |

4. | None of the above |

Subtopic: Conduction |

81%

From NCERT

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