Title THERMAL PHYSICS.pdf ✅

Thermal Physics  Digital www.allendigital.in [ 95 ] TEMPERATURE & THERMAL EXPANSION 1. At what temperature does the temperature in Celsius and Fahrenheit equalise (1) –40° (2) 40° (3) 36.6° (4) 38° 2. A difference of temperature of 25° C is equivalent to a difference of : (1) 45° F (2) 72° F (3) 32° F (4) 25° F 3. Which of the curves in figure represents the relation between Celsius and Fahrenheit temperature? (1) Curve a (2) Curve b (3) Curve c (4) Curve d 4. The graph AB shown in figure is a plot of temperature of a body in degree Celsius and degree Fahrenheit. Then (1) slope of line AB is 9/5 (2) slope of line AB is 5/9 (3) slope of line AB is 1/9 (4) slope of line AB is 3/9 5. Oxygen boils at –183°C. This temperature is approximately in Fahrenheit is :- (1) –329°F (2) –261°F (3) –215°F (4) –297°F 6. Using which of the following instrument, the temperature of the sun can be determined? (1) Platinum thermometer (2) Gas thermometer (3) Pyrometer (4) Vapour pressure thermometer 7. Two thermometers X and Y have ice points marked at 15° and 25° and steam points marked as 75° and 125° respectively. When thermometer X measures the temperature of a bath as 60° on it, what would thermometer Y read when it is used to measure the temperature of the same bath? (1) 60° (2) 75° (3) 100° (4) 90° 8. The figure below shows four isotropic solids having positive coefficient of thermal expansion. A student predicts that on heating the solid following things can happen. Mark true (T) or False (F) for comments made by the student. (i) The angle  in figure (1) will not change. (ii) The length of line in figure (2) will decrease. (iii) The radius of inner hole will decrease. (iv) The distance AB will increase. (1) T F F T (2) F T T F (3) T T T T (4) F F T F 9. At STP a rod is hung from a frame as shown in figure, leaving a small gap between the rod and floor. The frame and rod system is heated uniformly upto 350 K. Then (1) The rod will never touch the floor in any case. (2) If rod > frame, then rod may touch the floor. (3) If rod < frame, then rod may touch the floor. (4) None of the above 10. The volume of a metal sphere increases by 0.15% when its temperature is raised by 24°C.The coefficient of linear expansion of metal is : (1) 2.5 × 10–5/°C (2) 2.0 × 10–5/°C (3) –1.5 × 10–5/°C (4) 1.2 × 10–5/°C 11. Suppose there is a hole in a copper plate. On heating the plate, diameter of hole, would : (1) always increase (2) always decrease (3) always remain the same (4) none of these C c F a b d 32°F 212°F Fahrenheit A 100°C B Centigrade A B  Rod Exercise - I
NEET : Physics [ 96 ] www.allendigital.in  Digital 12. The table gives the initial length 0, change in temperature T and change in length  of four rods. Which rod has greatest coefficient of linear expansion Rod 0(m) T(°C) (m) A1 1 100 1 A2 1 100 2 A3 1.5 50 3 A4 2.5 20 4 (1) A1 (2) A2 (3) A3 (4) A4 13. An iron bar (Young’s modulus = 1011 N/m2,  = 10–6 /°C) 1 m long and 10–3 m2 in area is heated from 0°C to 100°C without being allowed to bend or expand. Find the compressive force developed inside the bar. (1) 10,000 N (2) 1000 N (3) 5000 N (4) 105 N 14. A rod of length 2m rests on smooth horizontal floor. If the rod is heated from 0°C to 20°C. Find the longitudinal strain developed? ( = 5 × 10–5/°C) (1) 10–3 (2) 2×10–3 (3) Zero (4) None CALORIMETRY 15. A body of mass 5 kg falls from a height of 30 metre. If its all mechanical energy is changed into heat, then heat produced will be:- (1) 350 cal (2) 150 cal (3) 60 cal (4) 6 cal 16. A bullet moving with velocity v collides against wall. consequently half of its kinetic energy is converted into heat. If the whole heat is acquired by the bullet, the rise in temperature will be:– (1) v2/4S (2) 4v2/2S (3) v2/2S (4) v2/S 17. The amount of heat required in converting 1 g ice at –10°C into steam at 100°C will be :– (1) 3028 J (2) 6056 J (3) 721 J (4) 616 J 18. 2 kg ice at – 20°C is mixed with 5 kg water at 20°C. Then final amount of water in the mixture would be; Given specific heat of ice = 0.5 cal/g°C, Specific heat of water = 1 cal/g°C, Latent heat of fusion for ice = 80 cal/g. (1) 6 kg (2) 5 kg (3) 4 kg (4) 2 kg 19. Two identical masses of 5 kg each fall on a wheel from a height of 10m. The wheel disturbs a mass of 2kg water, the rise in temperature of water will be : (1) 2.6° C (2) 1.2° C (3) 0.32° C (4) 0.12° C 20. A block of mass 2.5 kg is heated to temperature of 500°C and placed on a large ice block. What is the maximum amount of ice that can melt (approx.). Specific heat for the body = 0.1 cal/g°C. (1) 1 kg (2) 1.5 kg (3) 2 kg (4) 2.5 kg 21. 1 kg of ice at –10°C is mixed with 4.4 kg of water at 30°C. The final temperature of mixture is: (specific heat of ice = 2100 J/kg-k) (1) 2.3°C (2) 4.4°C (3) 5.3°C (4) 8.7°C 22. The amount of heat required to convert 1 g of ice at 0°C into steam at 100°C, is (1) 716 cal. (2) 500 cal. (3) 180 cal. (4) 100 cal. 23. The latent heat for vapourisation for 1 g water is 536 cal. Its value in Joule/kg will be :- (1) 2.25 × 106 (2) 2.25 × 103 (3) 2.25 (4) None of these 24. If 10 g ice at 0°C is mixed with 10 g water at 20°C, the final temperature will be :- (1) 50°C (2) 10°C (3) 0°C (4) 15°C 25. 420 joule of energy supplied to 10 g of water will raise its temperature by nearly :- (1) 1°C (2) 4.2°C (3) 10°C (4) 42°C 26. A solid material is supplied with heat at a constant rate. The temperature of material is changing with heat input as shown in the figure. What does slope DE represent. (1) latent heat of liquid (2) latent heat of vapour (3) heat capacity of vapour (4) inverse of heat capacity of vapour Temperature A y B C D E O Heat Input x
Thermal Physics  Digital www.allendigital.in [ 97 ] 27. The graph shown in the figure represent change in the temperature of 5 kg of a substance as it absorbs heat at a constant rate of 42 kJ min–1. The latent heat of vaporization of the substance is : (1) 630 kJ kg–1 (2) 126 kJ kg–1 (3) 84 kJ kg–1 (4) 12.6 kJ kg–1 28. A block of ice with mass m falls into a lake. After impact, a mass of ice m/5 melts. Both the block of ice and the lake have a temperature of 0°C. If L represents the heat of fusion, the minimum distance the ice fell before striking the surface is (1) L 5g (2) 5L g (3) gL 5m (4) mL 5g 29. 10 g of ice at 0°C is kept in a calorimeter of water equivalent 10 g. How much heat should be supplied to the apparatus to evaporate the water thus formed? (Neglect loss of heat) (1) 6200 cal (2) 7200 cal (3) 13600 cal (4) 8200 cal 30. Figure shows the temperature variation when heat is added continuously to a specimen of ice (10 g) at –40 °C at constant rate. (Specific heat of ice = 0.53 cal/g °C and Lice = 80 cal/g, Lwater= 540 cal/g) Column–I Column–II (A) Value of Q1 (in cal) (P) 800 (B) Value of Q2 (in cal) (Q) 1000 (C) Value of Q3 (in cal) (R) 5400 (D) Value of Q4 (in cal) (S) 212 (T) 900 (1) A→S; B→P; C→Q; D→T (2) A→P; B→S; C→Q; D→R (3) A→P; B→S; C→R; D→Q (4) A→S; B→P; C→Q; D→R 31. The thermal capacity of any body is (1) a measure of its capacity to absorb heat (2) a measure of its capacity to provide heat (3) the quantity of heat required to raise its temperature by a unit degree (4) the quantity of heat required to raise the temperature of a unit mass of the body by a unit degree 32. 2 litre water at 27°C is heated by a 1 kW heater in an open container. On an average heat is lost to surroundings at the rate 160 J/s. The time required for the temperature to reach 77°C is (1) 8 min 20 sec (2) 10 min (3) 7 min (4) 14 min 33. A 2100 W continuous flow geyser (instant geyser) has water inlet temperature = 10°C while the water flows out at the rate of 20 g/s. The outlet temperature of water must be about (1) 20°C (2) 30°C (3) 35°C (4) 40°C 34. The ratio of coefficient of thermal conductivity of two different materials is 5:3. If the thermal resistance of rods of same area of these material is same, then what is ratio of length of these rods- (1) 3:5 (2) 5:3 (3) 25:9 (4) 9:25 35. Rate of heat flow through a cylindrical rod is Q1. Temperatures of ends of rod are T1 and T2. If all the linear dimensions of the rod become double and temperature difference remains same, it's rate of heat flow is Q2, then :– (1) Q1 = 2Q2 (2) Q2 = 2Q1 (3) Q2 = 4Q1 (4) Q1 = 4Q2 36. A heat flux of 4000 J/s is to be passed through a copper rod of length 10 cm and area of cross section 100 cm2. The thermal conductivity of copper is 400 W/m°C. The two ends of this rod must be kept at a temperature difference of (1) 1°C (2) 10°C (3) 100°C (4) 1000°C Temperature (°C) time (min) 0 5 10 15 20 25 30 35 40 4550 25 50 75 200 100 125 150 175 225 0 –40 Q1 Q2 Q3 Q4 100 Q(cal) Temp. (°C)
NEET : Physics [ 98 ] www.allendigital.in  Digital 37. The coefficient of thermal conductivity of copper is nine times that of steel. In the composite cylindrical bar shown in the figure what will be the temperature at the junction of copper and steel? (1) 75°C (2) 67°C (3) 33°C (4) 25°C 38. The figure shows the face and interface temperature of a composite slab containing of four layers of two materials having identical thickness. Under steady state condition, find the value of temperature  (1) 5°C (2) 10°C (3) –15°C (4) 15°C 39. Three rods made of the same material and having the same cross-section have been joined as shown in the figure. Each rod is of the same length. The left and right ends are kept at 0°C and 90°C respectively. The temperature of the junction of the three rods will be : (1) 45°C (2) 60°C (3) 30°C (4) 20°C 40. The coefficient of thermal conductivity depends upon- (1) Temperature difference of two ends (2) Area of the plate (3) Thickness of the plate (4) Material of the plate 41. Which of the following cylindrical rods will conduct most heat, when their ends are maintained at the same steady temperature (1) Length 1 m; radius 1 cm (2) Length 2 m; radius 1 cm (3) Length 2 m; radius 2 cm (4) Length 1 m; radius 2 cm 42. Gravitational force is required for – (1) Stirring of liquid (2) Convection (3) Conduction (4) Radiation 43. The layers of atmosphere are heated through - (1) Convection (2) Conduction (3) Radiation (4) 2 and 3 both 44. The lengths and radii of two rods made of same material are in the ratios 1 : 2 and 2 : 3 respectively. If the temperature difference between the ends for the two rods be the same then in the steady state. The amount of heat flowing per second through them will be in the ratio of (1) 1 : 3 (2) 4 : 3 (3) 8 : 9 (4) 3 : 2 45. Two metal rods, 1 & 2 of same length have same temperature difference between their ends, their thermal conductivities are K1 & K2 and cross sectional areas A1 & A2 respectively. What is required condition for same rate of heat conduction in them. (1) K1 = K2 (2) K1 A1 = K2 A2 (3) 1 2 1 2 K K = A A (4) 1 2 2 2 1 2 K K = 46. The temperature of hot and cold end of a 20 cm long rod in thermal steady state are at 100°C and 20°C respectively. Temperature at the centre of the rod is (1) 50°C (2) 60°C (3) 40°C (4) 30°C 47. Consider a compound slab consisting of two different materials having equal thicknesses and thermal conductivities K and 2K, respectively. The equivalent thermal conductivity of the slab is (1) 3K (2) 4 3 K (3) 2 3 K (4) 2K 48. Under steady state, the temperature of a body (1) Increases with time (2) Decreases with time (3) Does not change with time and is same at all the points of the body (4) Does not change with time but is different at different points of the body 49. The area of the glass of a window of a room is 10m2 and thickness 2 mm. The outer and inner temperature are 40°C and 20°C respectively. Thermal conductivity of glass in MKS system is 0.2 then heat flowing in the room per second will be - (1) 3 × 104 joules (2) 2 × 104 joules (3) 30 joules (4) 45 joules 100°C copper steel 0°C 18 cm 6 cm k = thermal conductivity k 2k k 2k 20°C 10°C  –5°C –10°C 90°C 90°C 0°C