CBSE
Multiple Choice QuestionsIf temperature of the sun were to increase from T to 2 T and its radius from R to 2R, then how many times the radiant energy will be received on the earth ?
4
16
32
64
Consider a compound slab consisting of two, different materials having equal lengths, thicknesses and thermal conductivities K and 2 K respectively. The equivalent thermal conductivity of the slab is
3 K
A black body has a wavelength of λ at temperature 2000 K. Its corresponding wavelength at temperature 3000 K will be
A block of ice at - 10°C is slowly heated and converted to steam at 100°C. Which of the following curves represents this phenomenon qualitatively ?
In which mode of transmission, the heat waves travel along straight line with the speed of light?
thermal radiation
forced convection
natural convection
thermal conduction
An ideal black body at room temperature is thrown into a furnance. It is observed that
it is the darkest body at all times
it cannot be distinguished at all times
initially it is the darkest body and later it becomes brightest
initially it is the darkest body and later it cannot be distinguished
An ice box made of Styrofoam (Thermal conductivity = 0.01Jm-1 s-1 K-1 ) is used to keep liquids cool. It has a total wall area including lid of 0.8 m and wall thickness of 2.0 cm. A bottle of water is placed in the box and filled with ice. If the outside temperature is 30°C the rate of flow of heat into the box is (in J-s-1 )
16
14
12
10
A copper block of mass 4 kg is heated in a furnance to a temperature 425°C and then placed on a large ice block. The mass of ice that will melt in this process will be (Specific heat of copper = 500 J kg-1 ° C-1 and heat of fusion of ice = 336 kJ kg-1 )
0.5 kg
1 kg
1.5 kg
2.5 kg
An electric water kettle rated 2.1 kW is filled with 1.5 kg of water at 20°C. How many seconds does it take to reache boiling point of water ? Assume that there are no heat losses from the kettle. Specific heat capacity of water is 4200 Jkg-1 K-1 .
60
120
240
480
A brass rod of length 500 mm and diameter 3 mm is joined to a steel rod of same length and diameter at 50°C. If the coefficients of linear expansion of brass and steel are 2.5 x 10-5 ° C-1 and 1.25 x 10-5 ° C-1 , then change in length of the combined rod at 200°C is
2.4 mm
2.8 mm
3.2 mm
3.6 mm
