105 practice questions covering Heat Transfer in Nature, organised into 0 topics.
105 questions include a written explanation.
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Sample questions
Q1
medium
Read these two statements about a room being warmed by a heater standing on the floor. (i) Air warmed by the heater rises towards the ceiling. (ii) Cooler air moves in near the floor to take its place. Which of these is correct?
ABoth (i) and (ii)
BOnly (i)
CNeither (i) nor (ii)
DOnly (ii)
Show answer and explanation
Correct answer: A - Both (i) and (ii)
Both statements describe the two halves of the same convection current. Warm air is lighter for its size and climbs, and the cooler air near the floor slides in to replace it, only to be heated and rise as well. Rejecting either statement would break the circulation that actually warms the room.
Q2
medium
Assertion (A): A person standing beside a bonfire can feel its heat on the exposed skin. Reason (R): Air is a poor conductor of heat.
ABoth A and R are true, and R is the correct explanation of A
BBoth A and R are true, but R is not the correct explanation of A
CA is true, but R is false
DA is false, but R is true
Show answer and explanation
Correct answer: B - Both A and R are true, but R is not the correct explanation of A
Both statements are true on their own. The warmth is felt because the fire sends out radiation, which crosses the gap in straight lines. That air conducts heat poorly is a fact, but it explains why conduction is not the route rather than why the warmth is felt, so R does not explain A.
Q3
medium
The same wax-and-rod demonstration is repeated using a wooden rod of the same size and the same flame. What is most likely to happen?
AThe wax pieces fall much sooner than they did on the metal rod
BThe wax pieces hardly melt, because wood conducts heat poorly
CAll the wax pieces fall together as soon as the flame is lit
DThe wax pieces fall in the reverse order, from the far end first
Show answer and explanation
Correct answer: B - The wax pieces hardly melt, because wood conducts heat poorly
Wood is a poor conductor, so heat crawls along it and very little reaches the wax pieces further down. They therefore stay in place while the wood near the flame chars. Heat cannot travel faster through wood than through metal, and it never skips to the far end first or arrives everywhere at once.
Q4
easy
Standing a little away from a glowing tandoor oven, a person feels the heat on the face at once. The main mode of heat transfer here is
Ainsulation
Bconvection
Cradiation
Dconduction
Show answer and explanation
Correct answer: C - radiation
Heat that crosses a gap of air and is felt immediately on the exposed side of the body is radiation, which travels in straight lines like light. Conduction through air is far too slow to be felt at a distance. Convection carries warm air upward rather than sideways to the face, and insulation is the blocking of heat.
Q5
easy
A woollen sweater keeps us warm in winter mainly because
Awool pulls heat out of the cold air outside
Bwool produces heat as soon as it is worn
Cwool is at a higher temperature than the body
Dwool and the air trapped in it are poor conductors, so body heat escapes slowly
Show answer and explanation
Correct answer: D - wool and the air trapped in it are poor conductors, so body heat escapes slowly
Wool and the still air caught between its fibres both conduct heat badly, so the warmth made by the body leaks away slowly. No cloth makes heat of its own, and heat never flows from cold outside air into a warmer body. A sweater lying on a chair is at room temperature, not above body temperature.
Q6
hard
A lighted candle stands at the bottom of a tall box that has two open chimneys on its top. A smoking incense stick is held over one chimney. The smoke is drawn down that chimney and later streams out of the other one. This shows that
Athe candle flame attracts smoke towards itself
Bhot air sinks to the bottom while cold air rises to the top
Cthe empty box sucks in anything held near its openings
Dcool air sinks down one chimney and warm air rises out of the other, making a moving current
Show answer and explanation
Correct answer: D - cool air sinks down one chimney and warm air rises out of the other, making a moving current
The candle warms the air above it, that warm air rises and escapes through one chimney, and cooler air is drawn in through the other to replace it, carrying the smoke with it. The smoke simply traces this circulation. A flame does not attract smoke, an open box does not suck air in by itself, and hot air rises rather than sinks.
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