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Following graph shows the correct variation in intensity of heat radiations by black body and frequency at a fixed temperature

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Important Questions on Thermal Properties of Matter

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

If a piece of metal is heated to temperature

θ

and then allowed to cool in a room which is at temperature

θ_{0}

, the graph between the temperature

T

of the metal and time

t

will be closest to :

MEDIUM

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

The power radiated by a black body is P and it radiates maximum energy at wavelength,

λ_{0}

. If the temperature of the black body is now changed so that it radiates maximum energy at wavelength

\frac{3}{4} λ_{0}

, the power radiated by it becomes nP. The value of n is

MEDIUM

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

A black body is at a temperature of

5760 K.

The energy of radiation emitted by the body at wavelength

250 nm

U_{1}

, at wavelength

500 nm

U_{2}

and that at

1000 nm

U_{3}

. Wien's constant,

b = 2.88 \times 10^{6} nm K.

Which of the following is correct?

MEDIUM

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

A current of $0.1 A$ flows through a $25 Ω$ resistor represented by the circuit diagram. The current in the $80 Ω$ resistor is:

Question Image

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

Ordinary bodies

A

and

B

radiate maximum energy with wavelength difference

4 μ m

. The absolute temperature of body

A

3

times that of

B

. The wavelength at which body

B

radiates maximum energy is

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

Two spherical black bodies have radii

r_{1}

and

r_{2}

. Their surface temperatures are

T_{1}

and

T_{2}

. If they radiate same power then

\frac{r_{2}}{r_{1}}

MEDIUM

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

A body cools from

{50.0}^{o} C

{49.9}^{o} C

5 s.

How long will it take to cool from

{40.0}^{o} C

{39.9}^{o} C

? Assume the temperature of surroundings to be

{30.0}^{o} C

and Newton's law of cooling to be valid

HARD

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

Parallel rays of light of intensity

I = 912 W m^{- 2}

are incident on a spherical black body kept in surroundings of temperature 300 K. Take Stefan-Boltzmann constant

σ = 5.7 \times 10^{-8} W m^{- 2} K^{- 4}

and assume that the energy exchange with the surroundings is only through radiation. The final steady state temperature of the black body is close to

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

A black body has maximum wavelength

λ_{m}

at temperature

2200 K .

Its corresponding wavelength at temperature

3300 K

will be

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

The plots of intensity versus wavelength for three black bodies at temperature $T_{1}$ , $T_{2}$ , $T_{3}$ , respectively, are shown in the figure. Their temperatures are such that

Question Image

MEDIUM

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

X g

of ice at

0^{o} C

is added to 340g of water at

20^{o} C

. The final temperature of the resultant mixture is

5^{o} C

. The value of

X

(in g) is closest to

[Heat of fusion of ice

= 333 J / g

; Specific heat of water

= 4.184 J / g . K

]

MEDIUM

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

Three stars

A, B, C

have surface temperatures

T_{A}, T_{B}, T_{C}

respectively. Star A appears bluish, star

B

appears reddish and star

C

yellowish. Hence,

MEDIUM

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

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 doubled, the power radiated in watt would be

MEDIUM

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

Two bottles

A

and

B

have radii

R_{A}

and

R_{B}

and heights

h_{A}

and

h_{B}

respectively with

R_{B} = 2 R_{A}

and

h_{B} = 2 h_{A}

. These are filled with hot water at

60 ° C

. Consider that heat loss for the bottles takes place only from side surfaces. If the time the water takes to cool down to

50 ° C

t_{A}

and

t_{B}

for bottles

A

and

B

, respectively, then

t_{A}

and

t_{B}

are best related as,

HARD

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

A black coloured solid sphere of radius $R$ and mass $M$ is inside a cavity with a vacuum inside. The walls of the cavity are maintained at temperature $T_{0}$ . The initial temperature of the sphere is $3 T_{0}$ . If the specific heat of the material of the sphere varies as $α T^{3}$ per unit mass with the temperature $T$ of the sphere, where $α$ is a constant, then the time taken for the sphere to cool down to temperature $2 T_{0}$ will be

( $σ$ is Stefan Boltzmann constant)

MEDIUM

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

Two identical beakers

A

and

B

contain equal volumes of two different liquids at

60 ° C

each and left to cool down. Liquid in

A

has density of

8 \times 10^{2} k g m^{- 3}

and specific heat of

2000 J k g^{- 1} K^{- 1}

while the liquid in

B

has density

10^{3} k g m^{- 3}

and specific heat of

4000 J k g^{- 1} K^{- 1}

. Which of the following best describes their temperature versus time graph schematically? (assume the emissivity of both the beakers to be the same)

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

The instrument used to regulate temperature to a particular degree is called:

1. Thermostat

2. Thermometer

3. Pyrometer

4. Thermocouple

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

The wavelength of the radiation emitted by a black body is

6 mm

and Wein's constant is

3 \times 10^{- 3} mK .

Then temperature of black body is

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

In the case of black body for energy distribution, energy radiated by a blackbody which is given by, Planck's formula reduces to Rayleigh Jean's formula for

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

On observing light from three different stars

P

Q

and

R

, it was found that intensity of violet colour is maximum in the spectrum of

P

, the intensity of green colour is maximum in the spectrum of

R

and the intensity of 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 :

Following graph shows the correct variation in intensity of heat radiations by black body and frequency at a fixed temperature

Important Questions on Thermal Properties of Matter

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