Physics - Thermal Properties Matter - Quiz-5

The ratio of energy of emitted radiation of a black body at 27 $° C$ and 927 $° C$ is

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() 1 : 4
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() 1 : 16
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() 1 : 64
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() 1 : 256

Two spherical black bodies of radii $r_{1}$ and $r_{2}$ and with surface temperature $T_{1}$ and $T_{2}$ respectively radiate the same power. Then the ratio of $r_{1}$ and $r_{2}$ will be
(a) ${(\frac{T_{2}}{T_{1}})}^{2}$ (b) ${(\frac{T_{2}}{T_{1}})}^{4}$
(c) ${(\frac{T_{1}}{T_{2}})}^{2}$ (d) ${(\frac{T_{1}}{T_{2}})}^{4}$

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4

A black body is at a temperature 300 K. It emits energy at a rate, which is proportional to
(a) 300 (b) ${(300)}^{2}$
(c) ${(300)}^{3}$ (d) ${(300)}^{4}$

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Two identical metal balls at temperature 200 $° C$ and 400 $° C$ kept in air at 27 $° C$ . The ratio of net heat loss by these bodies is

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1/4
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1/2
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1/16
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$\frac{473^{4} - 300^{4}}{673^{4} - 300^{4}}$

The radiation emitted by a star A is 10,000 times that of the sun. If the surface temperatures of the sun and the star A are 6000 K and 2000 K respectively, the ratio of the radii of the star A and the sun is

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300 : 1
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600 : 1
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900 : 1
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1200 : 1

Star A has radius r surface temperature T while star B has radius 4r and surface temperature T/2. The ratio of the power of two stars, $P_{A}$ : $P_{B}$ is

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16 : 1
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1 : 16
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1 : 1
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1 : 4

Suppose the sun expands so that its radius becomes 100 times its present radius and its surface temperature becomes half of its present value. The total energy emitted by it then will increase by a factor of

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$10^{4}$
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625
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256
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16

If the temperature of the body is increased from –73 $° C$ to 327 $° C$ , then the ratio of energy emitted per second in both cases is :

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1 : 3
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1 : 81
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1 : 27
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1 : 9

If the sun’s surface radiates heat at $6.3 \times 10^{7} {Wm}^{- 2 then t}$ he temperature of the sun, assuming it to be a black body, will be:
$(σ = 5.7 \times 10^{- 8} {Wm}^{- 2} K^{- 4})$

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$5.8 \times 10^{3} K$
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$8.5 \times 10^{3} K$
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$3.5 \times 10^{8} K$
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$5.3 \times 10^{8} K$

The value of Stefan’s constant is
(a) $5.67 \times 10^{- 8} W / m^{2} - K^{4}$ (b) $5.67 \times 10^{- 5} W / m^{2} - K^{4}$
(c) $5.67 \times 10^{- 11} W / m^{2} - K^{4}$ (d) None of these

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4

Rate of cooling at 600K, if surrounding temperature is 300K is R. The rate of cooling at 900K is

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$\frac{16}{3} R$
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2R
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3R
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$\frac{2}{3} R$

A black body of surface area 10 ${cm}^{2}$ is heated to 127°C and is suspended in a room at temperature 27°C. The initial rate of loss of heat from the body at the room temperature will be

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2.99 W
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1.89 W
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1.18 W
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0.99 W

Two identical objects A and B are at temperatures $T_{A}$ and $T_{B}$ respectively. Both objects are placed in a room with perfectly absorbing walls maintained at temperatures T( $T_{A}$ >T> $T_{B}$ ). The objects A and B attain temperature T eventually. Which one of the following is the correct statement?

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‘A’ only emits radiations while B only absorbs them until both attain temperature
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A loses more radiations than it absorbs while B absorbs more radiations than it emits until temperature T is attained
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Both A and B only absorb radiations until they attain temperature T
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Both A and B only emit radiations until they attain temperature T

When the body has the same temperature as that of surroundings

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It does not radiate heat
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It radiates the same quantity of heat as it absorbs
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It radiates less quantity of heat as it receives from surroundings
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It radiates more quantity of heat as it receives heat from surroundings

The spectral energy distribution of star is maximum at twice temperature as that of sun. The total energy radiated by star is

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Twice as that of the sun
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Same as that of the sun
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Sixteen times as that of the sun
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One sixteenth of sun

While finding specific heat capacity using a calorimeter, error might occur due to:

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absence of insulating lid
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absence of water equivalent
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both 1 and 2
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neither 1 nor 2

A bucket full of hot water cools from 75 $° C$ to 70 $° C$ in time $T_{1}$ , from 70 $° C$ to 65 $° C$ in time $T_{2}$ and from 65 $° C$ to 60 $° C$ in time $T_{3}$ , then

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$T_{1} = T_{2} = T_{3}$
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$T_{1} > T_{2} > T_{3}$
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$T_{1} < T_{2} < T_{3}$
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$T_{1} > T_{2} < T_{3}$

Consider two hot bodies, $B_{1}$ and $B_{2}$ which have temperatures of 100 $° C$ and 80 $° C$ respectively at t=0. The temperature of the surroundings is 40 $° C$ . The ratio of the respective rates of cooling $R_{1}$ and $R_{2}$ of these two bodies at t=0 will be:

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$R_{1} : R_{2} = 3 : 2$
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$R_{1} : R_{2} = 5 : 4$
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$R_{1} : R_{2} = 2 : 3$
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$R_{1} : R_{2} = 4 : 5$

Newton's law of cooling is a special case of

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Stefan's law
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Kirchhoff's law
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Wien's law
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Planck's law

In Newton's experiment of cooling, the water equivalent of two similar calorimeters is 10 gm each. They are filled with 350 gm of water and 300 gm of a liquid (equal volumes) separately. The time taken by water and liquid to cool from 70°C to 60°C is 3 min and 95 sec respectively. The specific heat of the liquid will be

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0.3 Cal/gm $\times$ °C
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0.5 Cal/gm $\times$ °C
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0.6 Cal/gm $\times$ °C
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0.8 Cal/gm $\times$ °C

Which of the following statements is true/correct ?

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During clear nights, the temperature rises steadily upward near the ground level
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Newton's law of cooling, an approximate form of Stefan's law, is valid only for natural convection
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The total energy emitted by a black body per unit time per unit area is proportional to the square of its temperature in the Kelvin scale
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Two spheres of the same material have radii 1m and 4m and temperatures 4000 K and 2000 K respectively. The energy radiated per second by the first sphere is greater than that radiated per second by the second sphere

The rates of cooling of two different liquids put in exactly similar calorimeters and kept in identical surroundings are the same if

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Different volumes of the liquids at the same temperature are taken
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Equal volumes of the liquids at the same temperature are taken
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The masses of the liquids are equal
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Equal masses of the liquids at the same temperature are taken

The temperature of a liquid drops from 365 K to 361 K in 2 minutes. Find the time during which temperature of the liquid drops from 344 K to 342 K . Temperature of room is 293 K
(a) 84 sec (b) 72 sec
(c) 66 sec (d) 60 sec

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Newton’s law of cooling, holds good only if the temperature difference between the body and the surroundings is

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Less than 10 $° C$
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More than 10 $° C$
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Less than 100 $° C$
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More than 100 $° C$

The temperature of a body falls from 50 $° C$ to 40 $° C$ in 10 minutes. If the temperature of the surroundings is 20 $° C$ , then temperature of the body after another 10 minutes will be-

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36.6 $° C$
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33.3 $° C$
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35 $° C$
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30 $° C$

A body takes 5 minutes to cool from 90 $° C$ to 60 $° C$ . If the temperature of the surroundings is 20 $° C$ , the time taken by it to cool from 60 $° C$ to 30 $° C$ will be.

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5 min
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8 min
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11 min
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12 min

An object is cooled from 75°C to 65°C in 2 minutes in a room at 30°C. The time taken to cool another object from 55°C to 45°C in the same room in minutes is -

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4
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5
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6
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7

A cane is taken out from a refrigerator at 0°C. The atmospheric temperature is 25°C. If $t_{1}$ is the time taken to heat from 0°C to 5°C and $t_{2}$ is the time taken from 10°C to 15°C, then

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$t_{1} > t_{2}$
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$t_{1} < t_{2}$
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$t_{1} = t_{2}$
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There is no relation

Two rods (one semi-circular and other straight) of same material and of same cross-sectional area are joined as shown in the figure. The points A and B are maintained at different temperature. The ratio of the heat transferred through a cross-section of a semi-circular rod to the heat transferred through a cross section of the straight rod in a given time is

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2 : $π$
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1 : 2
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$π$ : 2
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3 : 2

A wall is made up of two layers A and B. The thickness of the two layers is the same, but materials are different. The thermal conductivity of A is double than that of B. In thermal equilibrium the temperature difference between the two ends is 36 $° C$ . Then the difference of temperature at the two surfaces of A will be

(a) 6 $° C$ (b) 12 $° C$
(c) 18 $° C$ (d) 24 $° C$

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Practice Physics Quiz Questions and Answers

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Practice Physics Quiz Questions and Answers

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