# The power radiated by a black body is $$P$$ and it radiates maximum energy at wavelength ${}_{}$$$\lambda_0$$. Temperature of the black body is now changed so that it radiates maximum energy at the wavelength $$\frac{3}{4}\lambda_0$$. The power radiated by it now becomes $$nP$$. The value of $$n$$ is: 1. $$\frac{3}{4}$$ 2. $$\frac{4}{3}$$ 3. $$\frac{256}{81}$$ 4. $$\frac{81}{256}$$

Subtopic:  Wien's Displacement Law |
65%
From NCERT
NEET - 2018
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Two identical bodies are made of a material for which the heat capacity increases with temperature. One of these is at $$100~^{\circ}\mathrm{C}$$, while the other one is at $$0~^{\circ}\mathrm{C}.$$ If the two bodies are brought into contact, then assuming no heat loss, the final common temperature is:

 1 $$50~^{\circ}\mathrm{C}$$ 2 more than $$50~^{\circ}\mathrm{C}$$ 3 less than $$50~^{\circ}\mathrm{C}$$ but greater than $$0~^{\circ}\mathrm{C}$$ 4 $$0~^{\circ}\mathrm{C}$$
Subtopic:  Calorimetry |
64%
From NCERT
NEET - 2016
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A body cools from a temperature of $$3T$$ to $$2T$$ in $$10$$ minutes. The room temperature is $$T$$. Assuming that Newton's law of cooling is applicable, the temperature of the body at the end of the next $$10$$ minutes will be:

 1 $$\frac{7}{4}T$$ 2 $$\frac{3}{2}T$$ 3 $$\frac{4}{3}T$$ 4 $$T$$

Subtopic:  Newton's Law of Cooling |
72%
From NCERT
NEET - 2016
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A spherical black body with a radius of $$12$$ cm radiates $$450$$ W power at $$500$$ K. If the radius were halved and the temperature is doubled, the power radiated in watts would be:
1. $$450$$
2. $$1000$$
3. $$1800$$
4. $$225$$

72%
From NCERT
NEET - 2017
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The coefficient of linear expansion of brass and steel rods are $$\alpha_1$$ and $$\alpha_2$$. Lengths of brass and steel rods are $$L_1$$ and $$L_2$$ respectively. If $$(L_2-L_1)$$ remains the same at all temperatures, which one of the following relations holds good?
1. $$\alpha_1L_2^2=\alpha_2L_1^2$$
2. $$\alpha_1^2L_2=\alpha_2^2L_1$$
3. $$\alpha_1L_1=\alpha_2L_2$$
4. $$\alpha_1L_2=\alpha_2L_1$$

Subtopic:  Thermal Expansion |
88%
From NCERT
NEET - 2016
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A black body is at a temperature of $$5760~\mathrm{K}$$. The energy of radiation emitted by the body at wavelength $$250~\mathrm{nm}$$ is $$U_1$$, at wavelength $$500~\mathrm{nm}$$ is $$U_2$$ and that at $$1000~\mathrm{nm}$$ is $$U_3$$. Wien’s constant, $$\mathrm{b}=2.88 \times 10^6 \mathrm{~nm}-\mathrm{K}$$. Which of the following is correct?
1. $$\mathrm{U}_3 =0$$
2. $$\mathrm{U}_1 >\mathrm{U}_2$$
3. $$\mathrm{U}_2 >\mathrm{U}_1$$
4. $$\mathrm{U}_1 =0$$
Subtopic:  Wien's Displacement Law |
64%
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. The value of $$h$$ is:
[Latent heat of ice is $$3.4 \times 10^5~\text{J/kg}$$ and $$g=10~\text{N/kg}$$]
1. $$544~\text{km}$$
2. $$136~\text{km}$$
3. $$68~\text{km}$$
4. $$34~\text{km}$$
Subtopic:  Calorimetry |
81%
From NCERT
NEET - 2016
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The value of the coefficient of volume expansion of glycerine is $$5\times10^{-4} \mathrm{~K^{-1}}$$. The fractional change in the density of glycerine for a rise of $$40^\circ \text{C}$$ in its temperature is:
1. $$0.015$$
2. $$0.020$$
3. $$0.025$$
4. $$0.010$$

Subtopic:  Thermal Expansion |
81%
From NCERT
NEET - 2015
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On observing light from three different stars $$P$$, $$Q$$, and $$R$$, it was found that the intensity of the violet colour is maximum in the spectrum of $$P$$, the intensity of the green colour is maximum in the spectrum of $$R$$ and the intensity of the red colour is maximum in the spectrum of $$Q$$. If $$T_P$$$$T_Q$$, and $$T_R$$ are the respective absolute temperatures of $$P$$, $$Q$$, and $$R$$, then it can be concluded from the above observations that:
1. $$T_P>T_Q>T_R$$
2. $$T_P>T_R>T_Q$$
3. $$T_P<T_R<T_Q$$
4. $$T_P<T_Q<T_R$$

Subtopic:  Wien's Displacement Law |
65%
From NCERT
NEET - 2015
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The two ends of a metal rod are maintained at temperatures $$100~^\circ\text{C}$$ and $$110~^\circ\text{C}.$$ The rate of heat flow in the rod is found to be $$4.0$$ J/s. If the ends are maintained at temperatures $$200~^\circ \text{C}$$ and $$210 ~^\circ \text{C},$$ 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 |
83%
From NCERT
NEET - 2015
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