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Assume that the mass density of the Sun is uniform and treat solar radiation as blackbody radiation. It's given that the surface temperature of the Sun is $6000 K$ and assume that the Sun continues giving energy at the same rate in future. If the source of Sun's radiated energy was its gravitational potential energy instead of the nuclear fusion then the Sun will cease to exist in a time of the order of

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Important Questions on Physics

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Reasoning and General Awareness>General Knowledge and Current Affairs>Physics>Heat and Thermodynamics

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

1. Thermostat

2. Thermometer

3. Pyrometer

4. Thermocouple

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Reasoning and General Awareness>General Knowledge and Current Affairs>Physics>Heat and Thermodynamics

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

HARD

Reasoning and General Awareness>General Knowledge and Current Affairs>Physics>Heat and Thermodynamics

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

Reasoning and General Awareness>General Knowledge and Current Affairs>Physics>Heat and Thermodynamics

During summer, water kept in an earthen pot becomes cool because of the phenomenon of:

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Reasoning and General Awareness>General Knowledge and Current Affairs>Physics>Heat and Thermodynamics

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 :

HARD

Reasoning and General Awareness>General Knowledge and Current Affairs>Physics>Heat and Thermodynamics

The maximum wavelength of radiation emitted by a star is

289.8 nm

. Then intensity of radiation for the star is (Given : Stefan’s constant =

5.67 \times 10^{- 8} W m^{- 2} K^{- 4}

, Wien’s constant,

b = 2898 μm K)

HARD

Reasoning and General Awareness>General Knowledge and Current Affairs>Physics>Heat and Thermodynamics

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)

EASY

Reasoning and General Awareness>General Knowledge and Current Affairs>Physics>Heat and Thermodynamics

Which one of the following is a bad Thermal Conductor?

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Reasoning and General Awareness>General Knowledge and Current Affairs>Physics>Heat and Thermodynamics

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

Reasoning and General Awareness>General Knowledge and Current Affairs>Physics>Heat and Thermodynamics

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}}

EASY

Reasoning and General Awareness>General Knowledge and Current Affairs>Physics>Heat and Thermodynamics

Temperature is measured by the instrument called _____.

EASY

Reasoning and General Awareness>General Knowledge and Current Affairs>Physics>Heat and Thermodynamics

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

Reasoning and General Awareness>General Knowledge and Current Affairs>Physics>Heat and Thermodynamics

The linear expansion of a solid rod is independent of its _____.

MEDIUM

Reasoning and General Awareness>General Knowledge and Current Affairs>Physics>Heat and Thermodynamics

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

Reasoning and General Awareness>General Knowledge and Current Affairs>Physics>Heat and Thermodynamics

Temperature is measured by the instrument called:

EASY

Reasoning and General Awareness>General Knowledge and Current Affairs>Physics>Heat and Thermodynamics

If temperature of a black body increases from

300 K

900 K

, then the rate of energy radiation increases by

MEDIUM

Reasoning and General Awareness>General Knowledge and Current Affairs>Physics>Heat and Thermodynamics

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

Reasoning and General Awareness>General Knowledge and Current Affairs>Physics>Heat and Thermodynamics

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

Reasoning and General Awareness>General Knowledge and Current Affairs>Physics>Heat and Thermodynamics

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,

MEDIUM

Reasoning and General Awareness>General Knowledge and Current Affairs>Physics>Heat and Thermodynamics

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?

Important Questions on Physics

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