Which one of the following statements best defines the concept of heat?
- A.The transformation of energy from one form to another
- B.The conversion of energy into mass and vice-versa due to temperature difference
- C.The transfer of energy due to temperature difference
- D.The change in volume of a substance with temperature
Correct answer
Explanation
The correct answer is C, The transfer of energy due to temperature difference. Heat is energy in transit: it flows from a hotter body to a colder one only because their temperatures differ, and stops when they reach the same temperature.
A body does not "contain" heat; it has internal energy, and heat is the part of it that moves across the boundary because of a temperature difference. Heat travels by conduction, convection and radiation. Its SI unit is the joule, though the calorie is still common: one calorie is about 4.186 joules. Temperature, by contrast, measures how hot or cold a body is.
A is wrong because changing energy from one form to another, as in a motor or a battery, describes energy conversion, not heat.
B is wrong because mass–energy conversion, E = mc², belongs to nuclear processes and is not caused by a temperature difference.
D is wrong because change of volume with temperature is thermal expansion, an effect of heating, not heat itself.
Exam tip: heat is energy that flows because of a temperature difference; temperature tells which way it flows.
Practice Questions
View allThe pressure exerted by a 760 mm column of mercury at 0 °C is known as
- A.1 pascal
- B.1 atmosphere
- C.1 bar
- D.1 poise
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Standard atmospheric pressure at sea level is defined as the pressure of a 760 mm column of mercury at 0 °C. In 1643 Evangelista Torricelli showed that air pressure holds up a column of mercury about 760 mm (76 cm) tall in a glass tube, inventing the mercury barometer.
Read the full explanation →Sound and light waves are
- A.respectively longitudinal and transverse in air
- B.respectively transverse and longitudinal in air
- C.both longitudinal in air
- D.both transverse in air
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Sound travels as compressions and rarefactions, while light is a transverse electromagnetic wave. In a longitudinal wave the particles of the medium vibrate back and forth along the direction in which the wave moves.
Read the full explanation →Which one of the following is the purest form of Carbon ?
- A.Charcoal
- B.Coke
- C.Fullerene
- D.Carbon black
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Fullerenes are made of carbon atoms alone, with no surface to trap other substances, so they are counted as the purest form of carbon.
Read the full explanation →A planet has a mass M₁ and radius R₁. The value of acceleration due to gravity on its surface is g₁. There is another planet 2, whose mass and radius both are two times that of the first planet. Which one of the following is the acceleration due to gravity on the surface of planet 2?
- A.g₁
- B.2g₁
- C.g₁/2
- D.g₁/4
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Surface gravity is g = GM/R², so doubling the mass doubles g while doubling the radius divides it by four, leaving g₁ × 2/4 = g₁/2.
Read the full explanation →Which one of the following is the major constituent of biogas ?
- A.Carbon dioxide
- B.Nitrous oxide
- C.Methane
- D.Oxygen
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Methane makes up the largest share of biogas, usually about 55 to 75 per cent, and it is the gas that burns.
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