# Two rods, one made of copper and other made of steel, of the same length and same cross sectional area are joined together. The thermal conductivity of copper and steel are $$385~\text{Js}^{-1}\text{K}^{-1}\text{m}^{-1}$$ and $$50~\text{Js}^{-1}\text{K}^{-1}\text{m}^{-1}$$ respectively. The free ends of copper and steel are held at $$100^\circ \text{C}$$ and $$0^\circ \text{C}$$ respectively. The temperature at the junction is, nearly: 1. $$12^\circ \text{C}$$ 2. $$50^\circ \text{C}$$ 3. $$73^\circ \text{C}$$ 4. $$88.5^\circ \text{C}$$

Subtopic:  Conduction |
70%
From NCERT
NEET - 2022
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A cup of coffee cools from $$90^{\circ}\mathrm{C}$$ $\mathrm{to}$ $$80~^{\circ}\mathrm{C}$$ in t minutes, when the room temperature is $$20^{\circ}\mathrm{C}$$$\mathrm{}$. The time taken by a similar cup of coffee to cool from $$80^{\circ}\mathrm{C}$$ $\mathrm{to}$ $$60^{\circ}\mathrm{C}$$ at room temperature same at $$20^{\circ}\mathrm{C}$$ is:
1. $$\frac{10}{13}t$$
2. $$\frac{5}{13}t$$
3. $$\frac{13}{10}t$$
4. $$\frac{13}{5}t$$

Subtopic:  Newton's Law of Cooling |
62%
From NCERT
NEET - 2021
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Consider a compound slab consisting of two different materials having equal thicknesses and thermal conductivities K and 2K, respectively. The equivalent thermal conductivity of the slab will be:

1. $2/6$ $\mathrm{K}$

2. $\sqrt{2}$ $\mathrm{K}$

3. $3\mathrm{K}$

4. $4/3$ $\mathrm{K}$

Subtopic:  Conduction |
71%
From NCERT
AIPMT - 2003
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We consider the radiation emitted by the human body. Which of the following statements is true:

 1 The radiation emitted is in the infrared region 2 The radiation is emitted only during the day 3 The radiation is emitted during the summers and absorbed during the winters 4 The radiation emitted lies in the ultraviolet region and hence is not visible
62%
From NCERT
AIPMT - 2003
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A cylindrical rod has temperatures ${\mathrm{T}}_{1}$ $\mathrm{and}$ ${\mathrm{T}}_{2}$ at its ends. The rate of flow of heat is ${Q}_{1}$ cal/sec. If all the linear dimensions are doubled while keeping the temperature constant, then the rate of flow of heat ${Q}_{2}$ will be:

1. $4{Q}_{1}$

2. $2{Q}_{1}$

3. $\frac{{Q}_{1}}{4}$

4. $\frac{{Q}_{1}}{2}$

Subtopic:  Conduction |
74%
From NCERT
AIPMT - 2001
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A black body has a wavelength ${\lambda }_{m}$ corresponding to maximum energy at 2000 K. Its wavelength corresponding to maximum energy at 3000 K will be:

1. $\frac{3}{2}{\lambda }_{m}$

2. $\frac{2}{3}{\lambda }_{m}$

3. $\frac{16}{81}{\lambda }_{m}$

4. $\frac{81}{16}{\lambda }_{m}$

Subtopic:  Wien's Displacement Law |
80%
From NCERT
AIPMT - 2001
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Unit of Stefan's constant is:

1. Watt-m2-K4

2. Watt-m2/K4

3. Watt/m2–K

4. Watt/m2 K4

Subtopic:  Stefan-Boltzmann Law |
77%
From NCERT
AIPMT - 2002
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Consider two rods of the same length and different specific heats $$(S_1,S_2)$$ conductivities $$(K_1,K_2)$$ and area of cross-sections $$(A_1,A_2)$$ and both having temperature $$T_1$$ and $$T_2$$ at their ends. If the rate of loss of heat due to conduction is equal, then:
1. $$K_1A_1=K_2A_2$$
2. $$\frac{K_1A_1}{S_1}=\frac{K_2A_2}{S_2}$$
3. $$K_2A_1=K_1A_2$$
4. $$\frac{K_2A_1}{S_2}=\frac{K_1A_2}{S_1}$$

Subtopic:  Conduction |
72%
From NCERT
AIPMT - 2002
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For a black body at a temperature of 727ºC, its radiating power is 60 watts and the temperature of the surroundings is 227ºC. If the temperature of the black body is changed to 1227ºC then its radiating power will be:

1. 304 W

2. 320 W

3. 240 W

4. 120 W

Subtopic:  Stefan-Boltzmann Law |
62%
From NCERT
AIPMT - 2002
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Which of the following is closest to an ideal black body?

 1 Black lamp 2 Cavity maintained at a constant temperature 3 Platinum black 4 A lump of charcoal heated to high temperature