Why birds are often seen to swell their features in winter?

Two bodies at different temperatures T₁ and T₂, if brought in thermal contact do not necessarily settle at the mean temperature \(\frac { ({ T }_{ 1 }+{ T }_{ 2 }) }{ 2 } \) . Why?

Usually a good conductor of heat is a good conductor of electricity also. Give reason.

Why the temperature above 1200⁰C cannot be measured accurately by a platinum resistance thermometer?

A tightened glass stopper can be taken out easily by pouring hot water around the neck of the bottle. Why?

Two thermos flasks are of the same height and same capacity. One has a circular cross-section while the other has a square cross-section. Which of the two is better?

The coolant used in a nuclear reactor should have high specific heat. Why?

Why it is much hotter above a fire than by its side?

The coefficient of volume expansion of glycerine is 49 x 10^-5 K^-1 .What is the fractional change in its density for a 30 °C rise in temperature ?

At what temperature (in ⁰C) Will be speed of sound air be 3 times its value at 0⁰ C?

A steel girder is 50 m long and has a cross-sectional area 250 cm² . What is the force exerted by the girder when heated from 5^oC to 25^o C ?

A metallic ball has a radius of 9.0 cm at 0⁰C. Calculate the change in its volume when it is heated to 90⁰ C. Given the coefficient of linear expansion of metal of ball is 1.2 x 10^-5 K.

A spherical black body with a radius of 12 em radiates 450 W power at 500 K. What would be tile power of radiation if radius were to be halved and the temperature doubled.

Good reflectors are poor emitters of thermal radiation. Explain

If the earth did not have an atmosphere it would become intolerable cold why?

Heat Flow through a Glass
Calculate the rate of loss of heat through a glass window of area 1000 cm²  and thickness 0.4 cm. When temperature inside is 37⁰ c and outside is -5⁰ C. Coefficient of thermal conductivity of glass is 2.2 x 10^-3 cal s^-1 cm^-1K^-1.

Aman went for a weekend trip with his parents and grandparents to a remote village. His grandfather showed him the fields and the crops they grow. As they moved forward, they saw that a bullock cart got struck in wet mud and the driver was not able to push it out by himself. Seeing him in distress, Aman ran to his help and together they pushed it out, but iron rim of the wheel came out.
They tried to put it on the wheel but it was smaller than diameter of wheel. Suddenly, he got an idea. He collected some wood and set them on fire and heated the rim and then rim easily slipped on the wheel. Cartman thanked Aman and moved away.
(i) What values of Aman does the incident show?
(ii) If the diameter of the rim and ring were 5.243 m and 5.231 m respectively at 27 \(^{0}\)C. To what temperature had Aman heated the ring so as to fit the rim of the wheel? Coefficient of linear expansion of iron = 1.20 x 10^-5 K^-1
(iii) Which property of solids is used in this phenomenon?

A resistance thermometer reads the resistance R= 20.0 \(\Omega \) , 27.5\(\Omega \)  and 50.0 \(\Omega \) at the ice point (0^o C), the steam point (100^o C) , the zinc point (420^o C), respectively. Assuming that the resistance varies with temperature as R_t = R_o \((1+\alpha t+\beta { t }^{ 2 })\) , where t is temperature in Celsius scale. Determine the value R_{o ,\(\alpha \) and \( \beta \) .}

A circular disc made by iron is rotating about its axis of rotation with a uniform angular speed \(\omega \)
Determine the change in the linear speed of particle at the rim in percentage. The disc of rim is slowly heated from 20^o C to 50^o C keeping the angular speed uniform. Give that coefficient of linear expansion for the material of iron is  \(1.2\times 10^{ -5\quad }\)\(^{0}\)C^-1