171.

Assertion: Woolen clothes keep the body warm in winter.

Reason:  Air is a bad conductor of heat.

• If both the assertion and reason are true and reason is a correct explanation of the assertion.

• If both assertion and reason are true but assertion is not a correct explanation of the assertion.

• If the assertion is true but the reason is false.

• If both assertion and reason are false.

A solid sphere and a hollow sphere are heated the same temperature. Point out the true statement.

• hollow sphere cools more quickly

• both hollow and solid sphere cools more quickly

• solid sphere cools more quickly

• none of the statement is true

1 Kcal of heat flowing through a rod iron. When the rod is cut down to 4 pieces then what will be the heat flowing through each piece having same differential temperature?

• 1/2 Kcal

• 1/4 Kcal

• 1 Kcal

• 1/15 Kcal

Temperature of the star is determined by

• distance

• colour

• size

• none of these

If hot water is mixed with cold water

• temperature first increases then become constant

• temperature first decreases then become constant

• increases continuously

• first it is uncertain then it become constant

A constant pressure air thermometer gave a reading 47.5 units of volume when immersed in ice-cold water and 67 units in a boiling liquid. The boiling point of the liquid, is

• 125^°C

• 100^°C

• 135^°C

• 112^°C

For an enclosure maintained at 1000 K, the maximum radiation occurs at wavelength λ_m. If the temperature is raised to 2000 K, the peak will shift to

• $\frac{5}{2}{\mathrm{\lambda }}_{\mathrm{m}}$

• $\frac{1}{2}{\mathrm{\lambda }}_{\mathrm{m}}$

• $\frac{7}{2}{\mathrm{\lambda }}_{\mathrm{m}}$

• $\frac{3}{2}{\mathrm{\lambda }}_{\mathrm{m}}$

A metallic solid sphere is rotating about its diameter as axes of rotation. If the temperature is increased by 200°C, the percentage increase in its moment of inertia is (Coefficient of linear expansion of the metal = ${10}^{-5}/°\mathrm{C}$)

• 0.1%

• 0.2%

• 0.3%

• 0.4%

A vessel containing 0.1 m³ of air at 76 cm of Hg is connected to an evacuated vessel of capacity 0.09m³. The resultant air pressure is

• 20 cm of Hg

• 30 cm of Hg

• 40 cm of Hg

• 60 cm of Hg

A black body of mass 34.38 g and surface area 19.2 cm² is at an initial temperature of 400 K. It is allowed to cool inside an evacuated enclosure kept at constant temperature 300 K. The rate of cooling is 0.04${}^{°}\mathrm{C}$/s. The specific heat of the body is (Stefan's constant σ = 5.73 × 10^-8 Jm^-2K^-4)

• 2800 J/kg-k

• 2100 J/kg-k

• 1400 J/kg-K

• 1200 J/kg-K