The unit of Stefan's constant is

• Wm^-2 K^-1

• Wm K^-4

• Wm^-2 K^-4

• Nm^-2 K^-4

A black body at 227°C radiates heat at the rate of 7 cal/cm² -s. At a temperature of 727°C. the rate of heat radiated in the same units will be

• 80

• 60

• 50

• 112

According to Newton's law of cooling, the rate of cooling of a body is proportional to ($\mathrm{\Delta \theta }$)ⁿ 1, where Δθ is the difference of the temperature of the body and the surroundings and n is equal to

• 2

• 3

• 4

• 1

Calculate the amount of heat (in calories) required to convert 5g of ice at 0°C to steam at 100°C

• 3100

• 3200

• 3600

• 4200

A beaker is completely filled with water at 4°C. It will overflow if:

• heated above 4°C

• cooled below 4°C

• both heated and cooled above and below 4°C respectively

• none of these

If the temperature difference on the two sides of a wall increases from 100°C to 200°C, its thermal conductivity :

• remains unchanged

• is doubled

• is halved

• becomes four times

Let there be four articles having colours blue, red, black and white. When they are heated together and allowed to cool, which article will cool at the earliest?

• Blue

• Red

• Black

• White

A piece of red glass when heated in dark to the red hot state will appear to be :

• White

• Red

• Green

• Invisible

The temperature of the black body increases from T to 2T. The factor by which the rate of emission will increase is

• 4

• 2

• 16

• 8

A body has initial temperature of 80°C. It cools by radiation process. In 5 minutes, it cools down to 64°C and in 10 minutes, it cools down to 52$°$C. The temperature of  surrounding is:

• 8°C

• 16$°$C

• 32$°$C

• 24$°$C