Thermodynamics PYQ — Page 6

Assuming the sun to have a spherical outer surface of radius $r$, radiating like a black body at temperature $t^{\circ} \mathrm{C}$, the power received by a unit surface, (normal to the incident rays) at a distance $R$ from the centre of the sun is: where $\sigma$ is the Stefan's constant

An engine has an efficiency of $1 / 6$. When the temperature of sink is reduced by $62^{\circ} \mathrm{C}$, its efficiency is doubled. Temperatures of the source is:

A Carnot engine whose sink is at $300 \mathrm{~K}$ has an efficiency of $40 \%$. By how much should the temperature of source be increased so as to increase its efficiency by $50 \%$ of original efficiency?

A black body at $1227^{\circ} \mathrm{C}$ emits radiations with maximum intensity at a wavelength of $5000 Å$. If the temperature of the body is increased by $1000^{\circ} \mathrm{C}$, the maximum intensity will be observed at:

The molar specific heat at constant pressure of an ideal gas is (7/2) $R$. The ratio of specific heat at constant pressure to that at constant volume is:

An ideal gas heat engine operates in carnot cycle between $227^{\circ} \mathrm{C}$ and $127^{\circ} \mathrm{C}$. It absorbs $6 \times 10^4$ cal of heat at higher temperature. Amount of heat converted into work, is:

Which of the following rods, (given radius $r$ and length $l$) each made of the same material and whose ends are maintained at the same temperature will conduct most heat?

The temperature of inversion of a thermocouple is $620^{\circ} \mathrm{C}$ and the neutral temperature is $300^{\circ} \mathrm{C}$. What is the temperature of cold junction?

Which of the following processes is reversible?

The equation of state for $5 \mathrm{~g}$ of oxygen at a pressure $P$ and temperature $T$, when occupying a volume $V$, will be: (where $R$ is the gas constant)

If $\lambda_m$ denotes the wavelength at which the radioactive emission from a black body at a temperature $T K$ is maximum, then:

One mole of an ideal gas at an initial temperature of $T~ K$ does $6~ R$ joules of work adiabatically. If the ratio of specific heats of this gas at constant pressure and at constant volume is $5 / 3$, the final temperature of gas will be:

Consider a compound slab consisting of two different materials having equal thickness and thermal conductivities $K$ and $2 K$, respectively. The equivalent thermal conductivity of the slab is:

We consider the radiation emitted by the human body. Which one of the following statement is true?

An ideal gas heat engine operates in a Carnot cycle between $227^{\circ} \mathrm{C}$ and $127^{\circ} \mathrm{C}$. It absorbs $6 \mathrm{kcal}$ at the higher temperature. The amount of heat (in kcal) converted into work is equal to:

Unit of Stefan's constant is:

The Wien's displacement law expresses the relation between:

The efficiency of the Carnot engine is $50 \%$ and the temperature of the sink is $500 \mathrm{~K}$. If the temperature of the source is kept constant and its efficiency raised to $60 \%$, then the required temperature of the sink will be:

For a black body at temperature $727^{\circ} \mathrm{C}$, its radiating power is $60 \mathrm{~W}$ and the temperature of surrounding is $227^{\circ} \mathrm{C}$. If temperature of the black body is changed to $1227^{\circ} \mathrm{C}$, then its radiating power will be:

Consider two rods of the same length and different specific heats $\left(S_1, S_2\right)$, conductivities $\left(K_1, K_2\right)$ and area of cross sections $\left(A_1, A_2\right)$ and both having temperature $T_1$ and $T_2$ at their ends. If the rate of loss of heat due to conduction is equal then:

Which of the following is best close to an ideal black body?