Thermal Properties (Expansion Calorimetry Heat Transfer) — Practice Questions

Free NEET Physics multiple-choice questions on Thermal Properties (Expansion Calorimetry Heat Transfer). Attempt each question and reveal the answer with a full explanation.

The unit of emissivity is: Dimensionless W/m 2 J/s W/m 2 K 4 A bimetallic strip is made of brass and iron. When heated, it bends into an arc with the brass on the convex side. This is because: The coefficient of linear expansion of brass is greater than that of iron The coefficient of linear expansion of iron is greater than that of brass The density of brass is greater than iron Brass is a better conductor of heat than iron The unit of latent heat is: J/kg J/kg K J K kg/J If the ratio of the densities of two materials is 2:3 and the ratio of their specific heats is 1:2 , then the ratio of their thermal capacities per unit volume is: 1:3 1:2 3:2 4:3 A substance is in a solid state at 0 ∘ C . Heat is supplied to it at a constant rate and a graph of temperature versus time is plotted. The part of the graph that is horizontal represents: Phase change Specific heat capacity Thermal expansion Gas state The coefficient of linear expansion of a rod is α . If the temperature of the rod is increased by ΔT , the percentage increase in its volume is approximately: 3αΔT 100 αΔT 100 1 3 αΔT 100 3αΔT If the temperature of a star is doubled, the total power radiated by it increases by a factor of: 16 4 2 8 The value of coefficient of volume expansion of glycerin is 5 10 -4 K -1 . The fractional change in the density of glycerin for a rise of 40 C in its temperature, is: 0.020 0.025 0.010 0.015 A piece of glass is heated to a high temperature and then allowed to cool. If a graph is plotted between its temperature and time, it will be a: Exponential decay curve Straight line Hyperbola Parabola Two metal spheres of radii R 1 and R 2 are heated to the same temperature. They are allowed to cool in the same surroundings. The ratio of their initial rates of loss of heat is: R 1 2 : R 2 2 R 1 : R 2 R 1 3 : R 2 3 1 : 1 Which of the following substances has the highest specific heat? Water Ice Copper Mercury For a constant volume gas thermometer, the pressure of a gas at the triple point of water ( 273.16 K ) is P tr . If the pressure at another temperature T is P , then T (in Kelvin) is given by: 273.16 (P/P tr ) 273.16 (P tr /P) 273.16 + (P - P tr ) 273.16 (P/P tr ) According to Kirchhoff's law of radiation, for any body at a given temperature, the ratio of emissive power to absorptive power is: Equal to the emissive power of a black body at the same temperature Proportional to the square of the temperature Constant for all bodies but depends on wavelength Always equal to unity Steam at 100 C causes more severe burns than boiling water at 100 C because: Steam has latent heat of vaporization Steam is a gas Steam has higher specific heat Steam is at a higher temperature If the temperature of a star increases, the wavelength at which it emits maximum intensity radiation will: Shift towards shorter wavelengths (blue) Shift towards longer wavelengths (red) Remain unchanged Becomes zero Two metal rods 1 and 2 of same lengths have same temperature difference between their ends. Their thermal conductivities are K 1 and K 2 and cross-sectional areas A 1 and A 2 , respectively. If the rate of heat conduction in rod 1 is four times that in rod 2 , then: K 1 A 1 = 4 K 2 A 2 K 1 A 1 = K 2 A 2 4 K 1 A 1 = K 2 A 2 K 1 A 1 = 2 K 2 A 2 The coefficient of real expansion of a liquid is r and the coefficient of apparent expansion is a . If the coefficient of linear expansion of the vessel material is , then the correct relation is: r = a + 3 r = a - 3 a = r + 3 r = a + A black body at temperature T radiates power P . If the temperature is increased to 2T and the emissivity is halved, the new power radiated will be: 8P 16P 4P 2P 200 g of water at 80 C is mixed with 300 g of water at 20 C in a calorimeter of negligible heat capacity. The final temperature of the mixture is: 44 C 50 C 40 C 56 C A circular hole is drilled in a metal sheet. When the sheet is heated, the area of the hole: Increases Decreases Remains the same Increases or decreases depending on the thickness According to Wien's displacement law, if the absolute temperature of a black body is tripled, the wavelength corresponding to maximum emission becomes: 1/3 times 3 times 9 times 1/9 times Which of the following is the units of Stefan-Boltzmann constant? W m -2 K -4 W m 2 K -4 W m -2 K 4 W m 2 K 4 The coefficient of volume expansion of a liquid is . The fractional change in its density / for a temperature rise T is approximately: - T T T / 3 3 T A hot body cools from 90 C to 80 C in t 1 seconds and from 80 C to 70 C in t 2 seconds. If the room temperature is 25 C , then: t 1 < t 2 t 1 > t 2 t 1 = t 2 t 1 = 2t 2 A metal cube of side a and coefficient of linear expansion is heated by temperature T . The increase in its surface area is approximately: 12 a 2 T 6 a 2 T 4 a 2 T 2 a 2 T The quantity of heat required to raise the temperature of a unit mass of a substance by 1 C is called its specific heat. The water equivalent of a body of mass m and specific heat s is: ms m/s s/m ms According to Newton's law of cooling, the rate of loss of heat of a body is directly proportional to the temperature difference between the body and its surroundings. The unit of the proportionality constant k in the equation dQ/dt = k(T - T s) is: J/s K J/K s/K J s/K The greenhouse effect is primarily based on the fact that: Glass is transparent to short wavelength solar radiation but opaque to long wavelength infrared radiation Glass is opaque to all types of solar radiation Glass reflects all thermal radiation Glass conducts heat very rapidly to the interior According to Prevost's theory of heat exchange: All bodies at all temperatures above absolute zero emit and absorb radiation simultaneously A body only radiates heat when it is hotter than its surroundings A body only absorbs heat when it is colder than its surroundings Radiation ceases when a body reaches thermal equilibrium with its surroundings The specific heat of a substance at its critical temperature is: Infinite Zero Constant Negative A black body is at 727 C . It emits energy at a rate which is proportional to: (1000) 4 (727) 4 (727) 2 (1000) 2 Two rods of same length and transfer a given amount of heat Q in 10 s when they are joined as shown in figure (a). When they are joined as shown in figure (b), they will transfer same amount of heat in: 2.5 s 40 s 20 s 5 s A black body is at a temperature of 5760 K . The energy of radiation emitted by the body at wavelength 250 nm is U 1 , at wavelength 500 nm is U 2 and at 1000 nm is U 3 . Wien's constant, b = 2.88 10 6 nm , K . Which of the following is correct? U 2 > U 1 U 1 > U 2 U 3 > U 2 U 1 = 0 Specific heat of a substance at its boiling point is: Infinite Zero Constant Depends on mass When M gram of ice at 0 C is mixed with M gram of water at 100 C , the final temperature of the mixture is: 10 C 50 C 40 C 0 C Two metal rods of the same length and area of cross-section are connected in series. Their thermal conductivities are K 1 and K 2 . The equivalent thermal conductivity of the combination is: 2 K 1 K 2 K 1 + K 2 K 1 K 2 K 1 + K 2 K 1 + K 2 K 1 + K 2 2 If 10 g of ice at 0 C is mixed with 10 g of water at 10 C , the final temperature of the mixture is: 0 C 5 C 10 C -5 C The solar constant is approximately 1360 W/m 2 . If the distance between the Earth and the Sun were doubled, the solar constant would become: 340 W/m 2 680 W/m 2 2720 W/m 2 1360 W/m 2 Two metal rods of thermal conductivities K 1 and K 2 , having the same length and area of cross-section, are connected in parallel. The equivalent thermal conductivity of the system is: (K 1 + K 2)/2 (K 1 + K 2) 2K 1K 2 / (K 1 + K 2) K 1 K 2 A black body at 227 C radiates heat at the rate of 7 cal/cm 2 s . At a temperature of 727 C , the rate of heat radiated in the same units will be: 112 80 50 28 The amount of heat required to convert 1 g of ice at -10 C into steam at 100 C is: ( s ice = 0.5 cal/g C , L f = 80 cal/g , L v = 540 cal/g ) 725 cal 625 cal 720 cal 540 cal The wavelengths of maximum emission for two stars A and B are 4800 and 6000 respectively. If the temperature of star A is 5000 K , then the temperature of star B is: 4000 K 6250 K 3000 K 4800 K Molar specific heat capacity of a substance at its melting point is: Infinite Zero Finite and positive Negative Two cylinders of same material have their radii in the ratio 2:1 and lengths in the ratio 1:2 . If they are subjected to the same temperature difference, the ratio of their rates of heat flow is: 8:1 4:1 2:1 1:1 A black body emits maximum radiation at wavelength max at temperature T . If the temperature is increased to 2T , the wavelength of maximum emission will be: max / 2 2 max max / 4 4 max A black body at 1227 ∘ C emits radiations with maximum intensity at wavelength 5000 Å . If the temperature of the body is increased by 1000 ∘ C , the maximum intensity will be observed at: 3000 Å 4000 Å 2500 Å 6000 Å Newton's law of cooling is used to calculate the time taken by a body to cool from 60 ∘ C to 50 ∘ C . If the surrounding temperature is 30 ∘ C and it takes 10 minutes , how much more time will it take to cool from 50 ∘ C to 40 ∘ C ? 15 minutes 10 minutes 12 minutes 20 minutes A body cools from 50 ∘ C to 40 ∘ C in 5 minutes when the surrounding temperature is 20 ∘ C . In what time will it cool from 40 ∘ C to 30 ∘ C ? 9 minutes 5 minutes 7.5 minutes 10 minutes Two black bodies at temperatures T 1 and T 2 ( T 1 > T 2 ) are placed in an environment at T 0 . The ratio of their net rates of loss of heat is: (T 1 4 - T 0 4) / (T 2 4 - T 0 4) (T 1 - T 0) / (T 2 - T 0) T 1 4 / T 2 4 (T 1 2 - T 0 2) / (T 2 2 - T 0 2) According to Newton's law of cooling, a plot of (T - T s) versus time t (where T s is surrounding temperature) will be a: Straight line with negative slope Straight line with positive slope Parabola Exponential curve Two slabs A and B of equal surface area are placed one over the other. Their thicknesses are l 1, l 2 and thermal conductivities are K 1, K 2 . The thermal resistance of the composite slab is: (l 1/K 1A) + (l 2/K 2A) (l 1+l 2) / (K 1+K 2)A (K 1l 1 + K 2l 2) / A (l 1+l 2) / (K 1K 2)A Two slabs of thermal conductivities K and 2K and thickness L and 2L respectively are joined in series. The temperature of the free ends are T 1 and T 2 . The temperature of the interface is: (T 1 + T 2)/2 (2T 1 + T 2)/3 (T 1 + 2T 2)/3 (3T 1 + T 2)/4 Three rods of identical cross-sectional area and made of the same material form the sides of an isosceles triangle ABC right-angled at B . The points A and C are maintained at temperatures T and 2 T respectively. In the steady state, the temperature of point B is: T( 2 + 1) 2 T( 2 + 2) 3 3T 2 + 1 T 2 + 1 A solid body floats in a liquid at 0 C . When the temperature is increased, the body sinks. This happens because: The density of the liquid decreases faster than the density of the solid The density of the solid decreases faster than the density of the liquid The mass of the liquid decreases The volume of the solid decreases Two rods of same length and same area of cross-section are joined in series. Their thermal conductivities are in the ratio 2:3 . If the temperature of the free end of the first rod is 100 C and that of the second rod is 20 C , the temperature of the junction in steady state is: 68 C 50 C 60 C 40 C The ratio of the emissive power of a black body at 300 K and 600 K is: 1:16 1:4 1:8 1:2 If the temperature of a hot body is increased by 50 % , the amount of radiation emitted by it increases by approximately: 400 % 50 % 100 % 225 % Which of the following graphs correctly represents the variation of the coefficient of volume expansion of copper with temperature T (in K)? A curve that increases and then becomes constant at high temperatures A straight line passing through origin A straight line parallel to temperature axis A curve that decreases with temperature Two bodies A and B have thermal emissivities of 0.01 and 0.81 respectively. Their surface areas are same. They emit the same total radiant power. If the temperature of B is T B , then the temperature of A is: 3T B 9T B T B/3 T B/9 For a constant volume gas thermometer, the pressure of a gas at the triple point of water is 20 kPa . What is the pressure of the gas at the boiling point of water ( 373.15 K )? (Triple point = 273.16 K ) 27.32 kPa 14.64 kPa 40.00 kPa 20.00 kPa A spherical black body with a radius of 12 cm radiates 450 W power at 500 K . If the radius were halved and the temperature doubled, the power radiated in watt would be: 1800 225 450 900 The temperature of a body is increased from -73 C to 327 C . The ratio of energy emitted per second is: 1 : 81 1 : 3 1 : 9 1 : 27 Two metal rods X and Y of same length have their thermal conductivities in the ratio 2:3 and cross-sectional areas in the ratio 3:2 . What is the ratio of their thermal resistances? 1 : 1 4 : 9 9 : 4 2 : 3 The coefficient of linear expansion of brass and steel are 1 and 2 . If we take a brass rod of length L 1 and a steel rod of length L 2 , then the difference in their lengths (L 2 - L 1) will remain the same at all temperatures if: 1 L 1 = 2 L 2 1 L 2 = 2 L 1 1 2 L 1 = 2 2 L 2 1 L 1 2 = 2 L 2 2 The heat required to raise the temperature of 1 mole of an ideal gas at constant pressure by 10 C is Q p . The heat required to raise the temperature of the same gas at constant volume by 10 C is Q v . The relation between Q p and Q v is ( R is gas constant): Q p - Q v = 10R Q p - Q v = R Q v - Q p = 10R Q p = Q v A block of wood floats in a liquid with 1/4 of its volume outside the liquid. When the temperature of the liquid is increased, the block sinks further. This happens because: The density of the liquid decreases more than the density of the wood The density of the wood decreases more than the density of the liquid The surface tension of the liquid increases The viscosity of the liquid increases A piece of iron is heated in a flame. It first becomes dull red, then reddish yellow and finally white hot. The correct explanation for these changes is: Wien's Displacement Law Stefan's Law Kirchhoff's Law Newton's Law of Cooling Two bodies A and B are placed in an evacuated enclosure. The surface area of A is twice that of B , and the absolute temperature of A is half that of B . The ratio of the rate of radiant energy emitted by A to that by B is: 1 : 8 1 : 4 1 : 2 1 : 16 When 1 g of steam at 100 C is passed into 1 g of ice at 0 C , the final temperature of the mixture is: 100 C 50 C 80 C 0 C A cup of tea cools from 80 C to 60 C in 1 minute. The ambient temperature is 30 C . In next 1 minute, its temperature will be: 48 C 40 C 42 C 50 C An ice cube of mass 0.1 kg at 0 C is placed in an isolated container which is at 227 C . The specific heat s of the container varies with temperature T according to s = A + BT , where A = 100 cal/kg K and B = 2 10 -2 cal/kg K 2 . If the final temperature of the container is 27 C , the mass of the container is (Latent heat of fusion of ice = 8 10 4 cal/kg , Specific heat of water = 10 3 cal/kg K ): 0.495 kg 0.595 kg 0.695 kg 0.795 kg A pendulum clock keeps correct time at 20 C . If the temperature rises to 40 C , the clock will: (Coefficient of linear expansion of pendulum = 1.2 10 -5 / C ) Lose 10.37 seconds per day Gain 10.37 seconds per day Lose 5.18 seconds per day Gain 20.74 seconds per day The specific heat capacity of a metal at low temperatures varies with temperature T as C = kT 3 . The heat required to raise the temperature of n moles of the metal from T 1 to T 2 is: nk 4 (T 2 4 - T 1 4) nk 3 (T 2 3 - T 1 3) nk(T 2 4 - T 1 4) k 4 (T 2 4 - T 1 4) A rod of length L has a varying cross-sectional area A(x) = A 0 e ax . If the thermal conductivity is K , the thermal resistance of the rod is: 1 - e -aL KA 0 a e aL - 1 KA 0 a L KA 0 aL KA 0 Two bodies A and B have thermal emissivities of 0.01 and 0.81 respectively. The outer surface areas of the two bodies are same. The two bodies emit total radiant power at the same rate. The wavelength B corresponding to maximum spectral emissive power of B is shifted from the wavelength A corresponding to maximum spectral emissive power of A by 1.0 m . If the temperature of A is 5802 K , then: B = 1.5 m B = 0.5 m B = 0.25 m B = 1.0 m The rate of steady heat flow through a spherical shell of inner radius r 1 , outer radius r 2 , and thermal conductivity K , with temperatures T 1 and T 2 ( T 1 > T 2 ) is: 4 K r 1 r 2 (T 1 - T 2) r 2 - r 1 4 K (T 1 - T 2) r 2 - r 1 K (T 1 - T 2) 4 (r 2 - r 1) 4 K r 1 r 2 (T 1 - T 2) r 1 + r 2 Two spheres of different materials one with double the radius and one-fourth the wall thickness of the other are filled with ice. If the time taken by ice to melt completely at the same temperature is same, the ratio of thermal conductivities is: 1:8 8:1 1:4 4:1 Newton's law of cooling is a special case of: Stefan-Boltzmann Law Wien's Law Kirchhoff's Law Planck's Law A piece of ice falls from a height h so that it melts completely. Only one-quarter of the heat produced is absorbed by the ice and all energy of ice gets converted into heat during its fall. The value of h is ( L = 3.4 10 5 J/kg , g = 10 m/s 2 ): 136 km 34 km 68 km 544 km The density of a substance at 0 C is 10 g/cc and at 100 C its density is 9.7 g/cc . The coefficient of linear expansion of the substance is: 10 -4 / C 3 10 -4 / C 10 -3 / C 10 -2 / C Heat is flowing through a conductor of length l from x=0 to x=l . If its thermal conductivity K varies as K = K 0(1 + ax) , where a is a constant, then in steady state, the temperature gradient (dT/dx) is proportional to: (1 + ax) -1 (1 + ax) (1 + ax) -2 Constant A metal sphere and a metal cube of the same material and same mass are heated to the same temperature and allowed to cool in the same surroundings. The ratio of their initial rates of cooling is: ( /6) 1/3 : 1 1 : ( /6) 1/3 : 6 1 : 1 The temperature of an interface between two slabs of thickness d 1 and d 2 and thermal conductivities K 1 and K 2 in steady state is (where T 1 and T 2 are outer temperatures): (K 1 T 1/d 1 + K 2 T 2/d 2) / (K 1/d 1 + K 2/d 2) (K 1 T 1 + K 2 T 2) / (K 1 + K 2) (T 1 + T 2)/2 (d 1 T 1 + d 2 T 2) / (d 1 + d 2) The temperature of a metallic sphere of radius R is increased by a small amount T . If the linear coefficient of thermal expansion of the metal is , the approximate increase in the volume of the sphere is: 2 R 3 T 3 R 3 T 4 R 3 T 6 R 3 T The unit of the coefficient of thermal conductivity is: W m -1 K -1 J m K -1 W m K -1 J m -1 K -1