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Lokseva Pratishthan’s junior college, Class: XIIth Science, Date: 14/01/2022, Subject: Physics, , Phulgaon, Pune, Practice test (2021-22), , Marks: 25, Time: 1.30 hr., Seat No.:, , Instructions, The question paper is divided into four sections, Section A: Q.No.1 contains Four multiple choice type of questions carrying one mark each, Q.No.2 contains Three very short answer type of questions carrying one mark each, Section B: Q.No.3 to Q.No.08 contains Six short answer type of questions carrying two marks each, (Attempt any four), Section C: Q.No.09 to Q. No.11 contains Three short answer type of questions carrying three marks each, (Attempt any two), Section D: Q.No.12 to Q.No.13 contains Two long answer type of questions carrying four marks each, (Attempt any one), , Section A, Q1.Select and write the correct answer, , 04 marks, , (i). If a = 0.72 and r = 0.24, then the value of tr is, (a) 0.02 (b) 0.04 (c) 0.4 (d) 0.2, (ii). The ratio of emissive power of perfectly blackbody at 1327oC and 527oC is, (a) 4:1 (b) 16 : 1 (c) 2 : 1 (d) 8 : 1, (iii). A good reflector is a ............, (a) good absorber, (b) good transmitter, (c) poor absorber, (d) none of the above, (iv). For a perfect blackbody, (a) a = 1 (b) a=0 (c) r=1 (d) a <1, , Q2. Answer the following, 03 marks, (i).Why are the bottoms of cooking utensils blackened and tops polished?, (ii).Define emissive power., (iii).Define coefficient of Emission ., Section B, Attempt any Four, 08 marks, Q.3.State (i) Stefan-Boltmann law and (ii) Wein’s displacement law., Q.4. Calculate the energy radiated in one minute by a blackbody of surface area 200, cm2 at 127oC (σ = 5.7 × 10-8J m-2 s-1 K-4)., Q.5. What will happen to the mean square speed of the molecules of a gas if the, temperature of the gas increases?, Q.6. Define athermanous substances and diathermanous substances., Q.7. The difference between the two molar specific heats of a gas is 8000 J kg-1 K-1. If, the ratio of the two specific heats is 1.65, calculate the two molar specific heats., Q.8 Calculate the value of λmax for solar radiation assuming that surface temperature, of Sun is 5800 K (b = 2.897 ×10-3 m K). In which part of the electromagnetic, spectrum, does this value lie?

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Section C, Attempt any two, , 06 marks, , Q.9. Explain spectral distribution of blackbody radiation., Q.10. Compare the rate of loss of heat from a metal sphere at 827 ºC with the rate of, loss of heat from the same sphere at 427 ºC, if the temperature of the surrounding is 27, ºC., Q.11.(a)Coefficient of absorption (b)Coefficient of reflection (c)Coefficient of transmission, , Section D, Attempt any one, Q.12.State and prove Kirchoff’s law of heat radiation., Q13.What is a perfect blackbody ? How can it be realized in practice?, ********************, , 04 marks