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Thermal Properties of Matter MCQs for NEET — Physics Questions with Answers

Practice free Thermal Properties of Matter (Physics) NEET multiple-choice questions online with instant answers and detailed explanations. No login required.

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The wavelength of radiation emitted by a body depends upon

The nature of its surface

The area of its surface

The temperature of its surface

All the above factors

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Explanation

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Colour of shining bright star is an indication of its

Distance from the earth

Size

Temperature

Mass

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Explanation

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A black body at 200 K is found to exit maximum energy at a wavelength of $14 μm$ . When its temperature is raised to 1000K, the wavelength at which maximum energy is emitted is

$14 μm$

$70 μF$

$2.8 μm$

$2.8 nm$

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Explanation

(c) $λ_{m 1} T_{1} = λ_{m 2} T_{2} \Rightarrow λ_{m 2} = \frac{λ_{m 1} T_{1}}{T_{2}} = \frac{14 \times 200}{1000} = 2.8 μm$

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If the temperature of the sun becomes twice its present temperature, then

Radiated energy would be predominantly in infrared

Radiated energy would be predominantly in ultraviolet

Radiated energy would be predominantly in X-ray region

Radiated energy would become twice the present radiated energy

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Explanation

(b) The wavelength corresponding to maximum emission of radiation from the sun is $λ_{\max} = 4753 \overset{0}{A}$ (close to the wavelength of violet colour of visible region). Hence if temperature is doubled $λ_{m}$ is decreased $(λ_{m} \propto \frac{1}{T})$ i.e. mostly ultraviolet radiations emits.

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The maximum energy in the thermal radiation from a hot source occurs at a wavelength of $11 \times 10^{- 5}$ cm. According to Wein's law, the temperature of the source (on Kelvin scale) will be n times the temperature of another source (on Kelvin scale) for which the wavelength at maximum energy is $5.5 \times 10^{- 5}$ cm. The value n is

$\frac{1}{2}$

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Explanation

(c) $\frac{T_{1}}{T_{2}} = \frac{λ_{m 2}}{λ_{m 1}} = \frac{5.5 \times 10^{5}}{11 \times 10^{5}} = \frac{1}{2} \Rightarrow n = \frac{1}{2}$

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How is the temperature of stars determined by ?

Stefan’s law

Wein’s displacement law

Kirchhoff’s law

Ohm’s law

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Explanation

(b) The temperature of stars is determined by using the wavelength of light coming from them in Wan's displacement law.

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On increasing the temperature of a substance gradually, which of the following colours will be noticed by you ?

White

Yellow

Green

Red

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Explanation

(a)

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A black body has maximum wavelength $λ_{m}$ at temperature 2000 K. Its corresponding wavelength at temperature 3000 K will be

$\frac{3}{2} λ_{m}$

$\frac{2}{3} λ_{m}$

$\frac{4}{9} λ_{m}$

$\frac{9}{4} λ_{m}$

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Explanation

(b) $λ_{m_{2}} = \frac{T_{1}}{T_{2}} \times λ_{m_{1}} = \frac{2000}{3000} \times λ_{m_{1}} = \frac{2}{3} λ_{m_{1}} = \frac{2}{3} λ_{m}$

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A black body at a temperature of 1640 K has the wavelength corresponding to maximum emission equal to 1.75 $μm$ . Assuming the moon to be a perfectly black body, the temperature of the moon, if the wavelength corresponding to maximum emission is 14.35 $μ$ m is

100 K

150 K

200 K

250 K

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Explanation

(c) $\frac{T_{2}}{T_{1}} = \frac{λ_{m_{1}}}{λ_{m_{2}}} = \frac{1.75}{14.35} \Rightarrow T_{2} = \frac{1.75}{14.35} \times 1640 = 200 K$

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A particular star (assuming it as a black body) has a surface temperature of about $5 \times 10^{4} K$ . The wavelength in nanometers at which its radiation becomes maximum is -
(b = 0.0029 mK)

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Explanation

(b) According to Wein’s displacement law

$λ_{m} T = b or λ_{m} = \frac{b}{T} = \frac{0.0029}{5 \times 10^{4}} = 58 \times 10^{- 9} m = 58 nm$

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