116. Drinks kept in a vacuum flask remain hot or cold as the case may be for a long time because
(a) both walls are silvered on the vacuum side
(b) there is vacuum between the double walls
(c) the cork is a poor conductor of heat
(d) of all the above
Ans: (d)
117. A stone floor feels cold to the bare feet but a carpet on the same floor feels warm. This is because
(a) the floor and carpet are at different temperatures
(b) the stone conveys the heat away from the feet more rapidly than the carpet
(c) the carpet is a better conductor of heat than the stone
(d) the human body maintains a constant temperature
Ans: (b)
118. A bolometer is used to measure
(a) the quantity of heat energy in a body
(b) thermal radiations quantitatively
(c) high temperature
(d) the intensity of sound
Ans: (b)
119. Water has maximum density at
(a) 0° C
(b) -15° C
(c) 4° C
(d) 15° C
Ans: (c)
120. Body A is kept in contact with body B. Heat will flow from A to B if
(a) the heat content of A is greater than that of B
(b) the temperature of A is greater than that of B
(c) the specific heat of A is greater than that of B
(d) the specific heat of B is greater than that of A
Ans: (b)
121. Air escaping rapidly from a narrow orifice in an inflated tyre feels cool because
(a) the speed with which it escapes cools it down
(b) of the higher temperature of the surroundings
(c) of sudden expansion causing loss of internal energy
(d) there is no real fall in temperature
Ans: (c)
122. The atmosphere gets heated up mainly by
(a) direct sun’s rays
(b) radiation from earth’s surface
(c) radiogenic heat (resulting from radioactive decay)
(d) cosmic rays coming from space
Ans: (b)
123. The plants in a greenhouse are enclosed in a glass enclosure because
(a) glass allows the heat radiations of shorter wavelengths from the sun to pass through
(b) the plants absorb them – these shorter wavelengths – and reradiate them in the form of longer wavelengths
(c) the longer wavelengths cannot penetrate through the glass walls
(d) All the above
Ans: (d)
124. The cover of a solar cooker is made of glass because
(a) it absorbs sun’s rays
(b) it reflects sun’s rays
(c) it retains the heat inside by the greenhouse effect
(d) it radiates heat better than metals
Ans: (c)
125. The inside of both the walls of a thermos flask is silvered i.e., on the vacuum side in order to reduce heat loss by
(a) convection
(b) radiation
(c) conduction
(d) All the three
Ans: (b)
126. When ice just melts
(a) there is no change in volume
(b) there is no change in temperature
(c) heat is given out
(d) there is no change of state
Ans: (b)
127. Before the invention of geostationary satellites, television stations could not transmit their programmes to far off places because
(a) these signals are electromagnetic in nature
(b) these are not electromagnetic in nature
(c) their wavelength is very large
(d) they are not reflected by the ionosphere but pass through it
Ans: (d)
128. Heat transfer
(a) cools the body that transfers it
(b) heats the body that absorbs the heat
(c) may change the physical state of the substance
(d) All the above
Ans: (d)
129. The presence of impurities
(a) lowers the melting point of ice
(b) raises the melting point of ice
(c) has no effect on the melting point of ice
(d) may lower or raise the melting point depending upon the type of impurities
Ans: (a)
130. In a freezer ice cubes will be formed more quickly in trays made of
(a) rubber
(b) plastic
(c) aluminium
(d) wood
Ans: (c)