# Thermal Properties of Matter – Physics 9

## Thermal Properties of Matter – Physics 9

1.N molecules each of mass m of a gas Aand 2N molecules each of mass 2m of gas Bare contained in the same vessel which is maintained at temperature T. The mean square velocity of molecules of B type is v² and the mean square rectangular component of the velocity of A type is denoted by ω². Then ω²/v²

(a)2

(b)1

(c)1/3

(d)2/3

2.10 gm of ice cubes at 0°C are released in a tumbler(water equivalent 55 g) at 40°C.Assuming that negligible heat is taken from the surroundings, the temperature of water in the tumbler becomes nearly (L =80 cal/g)

(a)31°C

(b)22°C

(c)19°C

(d)15°C

3.A centigrade and a Fahrenheit thermometer are dipped in boiling water. The water temperature is lowered until theFahrenheit thermometer registers 140°. What is the fall in temperature as registered by the Centigrade thermometer?

(a)80°

(b)60°

(c)40°

(d)30°

4.Thermal capacity of 40 g of aluminum (s= 0.2 cal/g K) is

(a)168 joule /°C

(b)672 joule/°C

(c)840 joule/°C

(d)33.6 joule/°C

5.Mercury thermometer can be used to measure temperature up to

(a)260°C

(b)100°C

(c)357°C

(d)500°C

6.If the temperature of the sun is doubled, the rate of energy received on earth will be increased by a factor of

(a)2

(b)4

(c)8

(d)16

7.A body cools from 50.0°C to 48°C in 5s. How long will it take to cool from 40.0°C to 39°C?Assume the temperature of surroundings to be30.0°C and Newton’s law of cooling to be valid.

(a)2.5 s

(b)10 s

(c)20 s

(d)5 s

8.A beaker full of hot water is kept in a room. If itcoolsfrom80°C to 75°C in t1 minutes, from 75° C to 70°C in t2minutes and from 70°C to 65°C in t3minutes, then

(a)t1+t2+t3

(b)t1<t2=t3

(c)t1<t2<t3

(d)t1>t2>t3

9.A blackbody is at a temperature of 500 K. It emits energy at rate which is proportional to

(a)(500)²+²

(b)(500)³

(c)(500)²

(d)500

10.The radiant energy from the sun, incident normally at the surface of the earth is 20 kcal/m² min. What would have been the radiant energy, incident normally on the earth, if the sun had a temperature, twice of the present one?

(a)160 k cal/m²min

(b)40 k cal/m²min

(c)320k cal/m²min

(d)80 k cal/m²min

11.If 1 g of steam is mixed with 1 g of ice, then the resultant temperature of the mixture is

(a)270ºC

(b)230ºC

(c)100ºC

(d)50ºC

12.The coefficient of linear expansions of brass and steel are α1 and α2 respectively. When we take a brass rod of length *l*1 and a steel rod of length* l*2 at 0ºC, then the difference in their lengths(*l*2– *l*1) will remain the same at all temperatures if

(a)α1*l1=α2l2*

(b)α1*l2=α2l1*

(c)α1²*l1=α2l2*

(d)α1²*l1=α2/2l2/1*

13.The presence of gravitational field is required for the heat transfer by

(a)conduction

(b)stirring of liquids

(c)natural convection

(d)radiation

14.A black body has maximum wavelength λm at temperature 2000 K. Its corresponding wavelength at temperature 3000 K will be

(a)3/2λm

(b)2/3λm

(c)4/9λm

(d)9/4λm

15.A cylindrical rod having temperature T1and T2at its end. The rate of flow of heat is Q1cal/sec.If all the linear dimensions are doubled keeping temperature constant, then the rate of flow of heat Q2 will be

(a)4Q1

(b)2Q1

(c)Q1/4

(d)Q1/2

16.Wien’s law is concerned with

(a)the relation between emissivity and absorptivity of a radiating surface

(b)total radiation, emitted by a hot surface

(c)an expression for the spectral distribution of energy of a radiation from any source

(d)a relation between the temperature of a blackbody and the wavelength at which there is maximum radiant energy per unit wavelength

17.Radiation from which of the following sources, Atungstenapproximates black body radiation A tungsten

(a) lamp

(b)Sodium flame

(c)Hot lamp black

(d)A hole in a cavity maintained at constant temperature

18.Two rods of thermal conductivities K1 and K2, be equal cross-sections A1and A2and specific heats S1andS2are of equal lengths. The temperatures of two ends of each rod are T1and T2. The rate of flow of heat at the steady statbe equal if

(a)K1/A1S1=K2/A2S2

(b)K1A1=K2A2

(c)K1S1=K2S2

(d)A1S1=A2S2

19.Consider a compound slab consisting of two different materials having equal thicknesses and thermal conductivities Kand 2K, respectively.The equivalent thermal conductivity of the slab is

(a)4/3K

(b)2/3K

(c)√3K

(d)3 K

20.If λm denotes the wavelength at which the radiative emission from a black body at a temperature T Kis maximum, then

(a)λm∝T-¹

(b)λm∝T-4

(c)∝m is independent of T

(d)λm∝T

21.Which of the following circular rods (given radius and length l), each made of the same material and whose ends are maintained at the same temperature will conduct most heat?

(a)r= r0; l= l0

(b)r= 2r0; l= l0

(c)r= r0; l = 2l0

(d)r= 2r0; l= 2l0

22.The temperature of inversion of a thermocouple is 620°C and the neutral temperature is 300°C. What is the temperature of cold junction?

(a)320°C

(b)20°C

(c)–20°C

(d)40°C

23.A black body at 1227°C emits radiations with maximum intensity at a wavelength of 5000Å. If the temperature of the body is increased by 1000°C, the maximum intensity will be observed at

(a)5000Å

(b)6000Å

(c)3000Å

(d)4000Å

24.A black body is at 727°C. It emits energy at a rate which is proportional to

(a)(1000)4

(b)(1000)2

(c)(727)4

(d)(727)2

25.If the cold junction of a thermocouple is kept at 0°C and the hot junction is kept at T°C then the relation between neutral temperature (Tn) and temperature of inversion (Ti) is

(a)Tn= 2Ti

(b)Tn= Ti– T

(c)Tn= Ti+ T

(d)Tn= Ti/2

26.Assuming the sun to have a spherical outer surface of radius r, radiating like a black body at temperature t°C, the power received by a unit surface, (normal to the incident rays) at a distance R from the centre of the sun is

(a)r²σ(t+273)4/ 4πR²

(b)16π²r²σt4/R²

(c)r²σ(t-273)4/R²

(d)4πr²σt4/R²

where σ is Stefan’s constant.

27.On a new scale of temperature (which is linear)and called the W scale, the freezing and boiling points of water are 39° W and 239° W respectively. What will be the temperature on the new scale, corresponding to a temperature of 39° C on the Celsius scale?

(a)78° W

(b)117° W

(c)200° W

(d)139° W

28.An electric kettle takes 4A current at 220 V. How much time will it take to boil 1 kg of water from temperature 20°C? The temperature of boiling water is 100° C.

(a)6.3 min

(b)8.4 min

(c)12.6 min

(d)4.2 min

29.The two ends of a rod of length L and a uniform cross-sectional area A are kept at two temperatures T1 and T2(T1> T2). The rate of heat transfer, dQ/dt through the rod in a steady state is given by:

(a)dQ/dt=k(T1-T2)/LA

(b)dQ/dt=kLA(T1-T2)

(c)dQ/dt=kA(T1-T2)/L

(d)dQ/dt=kL(T1-T2)/A

30.A black body at 227°C radiates heat at the rate of 7 cals/cm²s. At a temperature of 727°C, the rate of heat radiated in the same units will be:

(a)50

(b)112

(c)80

(d)60

31.A cylindrical metallic rod in thermal contact with two reservoirs of heat at its two ends conducts an amount of heat Q in time t. The metallic rod is melted and the material is formed into a rod of half the radius of the original rod. What is the amount of heat conducted by the new rod, when placed in thermal contact with the two reservoirs in time t?

(a)Q/4

(b)Q/16

(c)2Q

(d)Q/2

32.The total radiant energy per unit area, normal to the direction of incidence, received at a distance R from the centre of a star of radius r, who seouter surface radiates as a black body at a temperature T K is given by:

(a)αr²T4/R²

(b)αr²T4/4πr²

(c)αr²T4/r²

(d)4παr²T4/R²

33.If the radius of a star is Rand it acts as a blackbody, what would be the temperature of the star, in which the rate of energy production is Q ?

(a)Q/4πR² α

(b)(Q/4πR²σ)-½

(c)(4πR²Q/σ)¼

(d)(Q/4πR²σ)¼

34.Liquid oxygen at 50 K is heated to 300 K at the constant pressure of 1 atm. The rate of heating is constant. Which one of the following graphs represents the variation of temperature with time?

(a)TemperatureTime

(b)TimeTemperature

(c)TemperatureTime

(d)TemperatureTime

35.A slab of stone of area0.36 m² and thickness0.1 m is exposed on the lower surface to steam at100°C. A block of ice at0°C rests on the upper surface of the slab. In one hour 4.8 kg of ice is melted. The thermal conductivity of slab is :(Given latent heat of fusion of ice = 3.36 ×10²+2+1 -¹Jkg.) :

(a)1.24 J/m/s/°C

(b)1.29 J/m/s/°C

(c)2.05 J/m/s/°C

(d)1.02 J/m/s/°C

36.A piece of iron is heated in a flame. It first becomes dull red then becomes reddish yellow and finally turns to white hot. The correct explanation for the above observation is possible by using

(a)Wien’s displacement law

(b)Kirchoff’s law

(c)Newton’s law of cooling

(d)Stefan’s law

37.The molar specific heats of an ideal gas at constant pressure and volume are denoted byCp and Cv, respectively. If γ= Cp/Cv and R is the universal gas constant, then Cv is equal to

(a)R/(γ -1)

(b)(γ -1)/R

(c)γR

(d)1+γ/1-γ

38.The density of water at 20°C is 998 kg/m³ and at40°C 992 kg/m³. The coefficient of volume expansion of water is

(a)10–4/°C

(b)3 × 10–4/°C

(c)2 × 10–4/°C

(d)6 × 10–4/°C

39.Two metal rods 1and 2 of same lengths have same temperature difference between their ends.Their thermal conductivities are K1and K2andcross sectional areas A1and A2, respectively. If the rate of heat conduction in rod 1is four times that in rod 2, then

(a)K1A1= K2A2

(b)K1A1 = 4K2A2

(c)K1A1 = 2K2A2

(d)4K1A1= K2A2

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