OBJECTIVE QUESTIONS FOR NEET AIIMS JIPMER www wisedane
OBJECTIVE QUESTIONS FOR NEET AIIMS JIPMER www. wisedane. com
PHYSICS HEAT AND THERMODYNAMICS SET 1 MCQ’S
Q 1. A faulty Thermometer has its fixed points marked 5 and 95. When this thermometer reads 68, the correct temperature in Celsius is : A. 68 o. C B. 70 o. C C. 66 o. C D. 72 o. C www. wisedane. com
ANSWER (B) EXPLANATION www. wisedane. com
Q 2. 200 gram of a solid ball at 20 o. C is dropped in an equal amount of water at 80 o. C. The resulting temperature is 60 o C. This means that specific heat of solid is A. One fourth of water B. One half of water C. Twice of water D. Four times of water. www. wisedane. com
ANSWER (B) EXPLANATION www. wisedane. com
Q 3. Equal masses of two liquids A and B contained in vessels of negligible heat capacity are supplied heat at the same rate. The temperature vs time graphs for the two liquid are shown in figure. if S represents sp. heat and L represents latent heat of liquid, then www. wisedane. com
ANSWER (D) EXPLANATION Ø As temperature of A rises faster than temperature of B, therefore, sp heat of A is less than that of B, i. e. , SA<SB. Horizontal portions of graphs represent conversion of liquid into vapours. Ø B. P. of A > BP of B. Therefore, LA>LB. www. wisedane. com
Q 4. Two liquids are at temps 20 o. C and 40 o. C. When same mass of both of them is mixed, the temperature of the mixture is 32 o. C. What is the ratio of their specific heats ? A. 1/3 B. 2/5 C. 3/2 D. 2/3 www. wisedane. com
ANSWER (D) EXPLANATION www. wisedane. com
Q 5. The height of Niagra fall is 50 m. The difference between the temperature of water at the top and the bottom of the fall is A. 117 o. C B. 11. 7 o. C C. 1. 17 o. C D. 0. 117 o. C www. wisedane. com
ANSWER (D) EXPLANATION www. wisedane. com
Q 6. The coefficient of apparent expansion of a liquid when heated in a copper vessel is C, and when heated in a silver vessel is S. If A is coefficient of linear expansion of copper, then the coefficient of linear expansion of silver is www. wisedane. com
ANSWER (B) EXPLANATION www. wisedane. com
A. 13. 12 g/cc B. 13. 65 g/cc C. 13. 51 g/cc D. 13. 22 g/cc www. wisedane. com
ANSWER (A) EXPLANATION www. wisedane. com
Q 8. Two metal rods A and B of equal lengths and equal cross sectional areas are joined end-to-end. The coefficients of thermal conductivity of A and B are in the ratio 2 : 3. When the free end of A is maintained at 100 o. C and the free end of B is maintained at 0 o. C, the temperature of the junction is: A. 30 o. C B. 40 o. C C. 50 o. C D. 60 o. C www. wisedane. com
ANSWER (B) EXPLANATION www. wisedane. com
Q 9. A cylindrical rod with one end in a steam chamber and the other end in ice results in melting of 0. 1 g of ice per second. If the rod is replaced by another with half the length and double the radius of the first and if thermal conductivity of the material of the second rod is ¼ that of the first, the rate at which ice melts in gm/sec will be A. 3 : 2 B. 1. 6 C. 0. 2 D. 0. 1 www. wisedane. com
ANSWER (C) EXPLANATION www. wisedane. com
Q 10. Two plates of same thickness, of coefficients of thermal conductivity K 1 and K 2 and areas of cross section A 1 and A 2 are connected as shown in figure. The common coefficient of thermal conductivity K will be www. wisedane. com
ANSWER (C) EXPLANATION www. wisedane. com
Q 11. Five rods of same dimensions are arranged as shown in Figure. They have thermal conductivities K 1, K 2, K 3, K 4 and K 5. When points A and B are maintained at different temperatures, no heat would flow through central rod, if www. wisedane. com
ANSWER (A) EXPLANATION www. wisedane. com
Q 12. The ratio of thermal conductivity of two rods of different materials is 5 : 4. The two rods of same area of cross section and same thermal resistance will have the lengths in the ratio A. 5 : 4 B. 1 : 9 C. 9 : 1 D. 4 : 5 www. wisedane. com
ANSWER (A) EXPLANATION www. wisedane. com
Q 13. Two metallic rods of same length, same material, same area of cross section are connected in (a) series (b) parallel. The conductivity of the combination would be (K is conductivity of each rod) A. 2 K, K/2 B. K/2, 2 K C. K, K D. 2 K, 2 K www. wisedane. com
ANSWER (C) EXPLANATION Ø The value of K depends only on nature of material. It would remain the same for series and parallel combinations. www. wisedane. com
Q 14. The temperature of coffee in a cup with time is most likely given by the curve in Figure www. wisedane. com
ANSWER (C) EXPLANATION Ø Fall of temperature with time follows an exponential curve as shown in figure. Ø This is as per Newton’s law of cooling. www. wisedane. com
Q 15. The temperature of a black body is increased by 50%, then the percentage increase of radiation is approximately A. 100% B. 25% C. 400% D. 500% www. wisedane. com
ANSWER (C) EXPLANATION www. wisedane. com
Q 16. A polished metal plate with a rough black spot on it is heated to about 1400 K and quickly taken to a dark room. The spot will appear A. Darker than plate B. Brighter than plate C. Equally bright D. Equally dark. www. wisedane. com
ANSWER (B) EXPLANATION Ø On heating, black spot absorbs max. radiation. Therefore, when plate is taken to a dark room, the spot will emit more radiations than the rest of the plate. Hence, it will appear brighter than the plate. www. wisedane. com
Q 17. A black body radiates at two temps T 1 and T 2, such that T 1<T 2. The frequency corresponding to max. intensity is A. Less at T 1 B. More at T 1 C. Equal in the two cases D. Cannot say. www. wisedane. com
ANSWER (A) EXPLANATION www. wisedane. com
Q 18. Two circular discs A and B with equal radii are blackened. They are heated to same temperature and are cooled under identical conditions. What inference do you draw from their cooling curves, Figure. A. A and B have same specific heats B. Sp. Heat of A is less C. Sp. Heat of B is less D. Nothing can be said www. wisedane. com
ANSWER (B) EXPLANATION Ø Cooling rate (R) is rate of fall of temperature, which according to Newton’s law varies inversely as sp. Ø Heat of the liquid. For A, rate of cooling is larger. Therefore, specific heat of A is less than specific heat of B. www. wisedane. com
Q 19. The frequency (vm) corresponding to which energy emitted by a black body is maximum may vary with temperature T of the body as shown in figure. which of the curves represents correct variation ? (a) A (b) B (c) C (d) D www. wisedane. com
ANSWER (A) EXPLANATION www. wisedane. com
Q 20. A body in laboratory takes 4 min. to cool from 61 o. C to 59 o. C. If the laboratory temp. is 30 o. C, then the time taken by it to cool from 51 o. C to 49 o. C is A. 4 min B. 6 min C. 8 min D. 5 min www. wisedane. com
ANSWER (B) EXPLANATION www. wisedane. com
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