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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Two rods $$\mathrm{P}$$ and $$\mathrm{Q}$$  of equal length and having cross-sections $$A_P$$ $$A_Q$$ respectively, have the same temperature difference across their ends. If $$k_P$$ $\mathrm{and}$ $$k_Q$$ are their thermal conductivities, then the condition for their equal rate of conduction of heat will be:
1. $$k_PA_P = k_QA_Q$$
2. $$\frac{\sqrt{k_P}}{A_P} - \frac{\sqrt{k_Q}}{A_Q}$$
3. $$k_PA_Q = k_QA_P$$
4. $$k^2_PA_P = k^2_QA_Q$$

Subtopic:  Conduction |
86%
From NCERT
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Three rods made of the same material and having the same cross-section have been joined as shown in the figure. Each rod has the same length. The left and right ends are kept at $$0^{\circ}\mathrm{C}$$ $and$ $$90^{\circ}\mathrm{C}$$, respectively. The temperature at the junction of the three rods will be:

1. $$45^{\circ}\mathrm{C}$$
2. $$60^{\circ}\mathrm{C}$$
3. $$30^{\circ}\mathrm{C}$$
4. $$20^{\circ}\mathrm{C}$$

Subtopic:  Conduction |
84%
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 |
80%
From NCERT
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The temperature of the hot and cold ends of a 20 cm long rod in a thermal steady state is at $$100^{\circ}\mathrm{C}$$ and $$20^{\circ}\mathrm{C}$$ respectively. The temperature at the centre of the rod will be:
1. $$50^{\circ}\mathrm{C}$$
2. $$60^{\circ}\mathrm{C}$$
3. $$40^{\circ}\mathrm{C}$$
4. $$30^{\circ}\mathrm{C}$$

Subtopic:  Conduction |
81%
From NCERT
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Two conducting slabs of heat conductivity $$K_{1} ~ \text{and} ~K_{2}$$ are joined as shown in fig. If the temperature at the ends of the slabs are $$\theta_{1}\ and\ \theta_{2} \ (\theta_{1} > \theta_{2} ),$$then the final temperature $$\left(\theta\right)_{m}$$of the junction will be:

 1 $$\frac{K_{1} \theta_{1} + K_{2} \theta_{2}}{K_{1} + K_{2}}$$ 2 $$\frac{K_{1} \theta_{2} + K_{2} \theta_{1}}{K_{1} + K_{2}}$$ 3 $$\frac{K_{1} \theta_{2} + K_{2} \theta_{1}}{K_{1} - K_{2}}$$ 4 None
Subtopic:  Conduction |
83%
From NCERT
AIPMT - 1999
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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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Four rods of the same material with different radii and length $\mathcal{l}$ are used to connect two heat reservoirs at different temperatures. In which of the following cases is the heat conduction fastest?

1. $r=\frac{1}{3}\mathrm{cm},$ $\mathcal{l}=\frac{1}{9}\mathrm{cm}$

2. r = 3 cm, $\mathcal{l}$ = 9 cm

3. r = 4 cm, $\mathcal{l}$ = 8 cm

4. r = 1 cm, $\mathcal{l}$ = 1 cm

Subtopic:  Conduction |
73%
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 |
74%
From NCERT
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Two slabs A and B of equal surface area are placed one over the other such that their surfaces are completely in contact. The thickness of slab A is twice that of B. The coefficient of thermal conductivity of slab A is twice that of B. The first surface of slab A is maintained at $$100^{\circ}\mathrm{C}$$$,$ while the second surface of slab B is maintained at $$25^{\circ}\mathrm{C}$$. The temperature at the common surface will be:
1. $$62.5^{\circ}\mathrm{C}$$
2. $$45^{\circ}\mathrm{C}$$
3. $$55^{\circ}\mathrm{C}$$
4. $$85^{\circ}\mathrm{C}$$

Subtopic:  Conduction |
72%
From NCERT
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