# Radiation Questions: Paper – 04

 1 Which one of the following constants is not related to radiation? (a) Solar constant (b) Stefan’s constant (c) Boltzmann’s constant (d) Wien’s constant Answer: (c) 2 Rate of cooling of body is 0.5°C/min, when the system is 50°C above the surroundings. When a system is 30°C above the surroundings, the rate of cooling will be (MHT-CET-2004) (a) 0.3°C/min (b) 0.6°C/min (c) 0.7°C/min (d) 0.4°C/min Answer: (a) 3 The sun emits light with a maximum wavelength of 510 nm while another star X emits light of maximum wavelength of 350 nm. What is the ratio of the surface temperatures of the sun and the star? (a) 0.35 (b) 1.5 (c) 1.1 (d) 0.69 Answer: (d) 4 A sphere cube and a thin circular plate all made of the same material and having the same mass are initially heated to a temperature of 300°C. which of these cools fastest? (MHT-CET-2000) (a) Sphere (b) Cube (c) Plate (d) None of these Answer: (c) 5 An extremely hot star would appear to be (a) Yellow (b) Orange (c) Blue (d) Red Answer: (c) 6 A body at higher temperature T°K radiates heat at a rate which is proportional to (MHT-CET-2001) (a) T (b) T2 (c) T–4 (d) T4 Answer: (d) 7 A black body emissive power is 81 J/m2 sec it is at 300 K another one ordinary body emissivity is 0.8 it is at 500 K then what is the emissive power of ordinary body? (MHT-CET-2008) (a) 200 J/m2 sec (b) 300 J/m2 sec (c) 400 J/m2 sec (d) 500 J/m2 sec Answer: (d) 8 Which one of the following constants is related to radiation? (a) Gravitational constant (b) Planck’s constant (c) Critical constant (d) Boltzmann’s constant Answer: (b) 9 If a black body is heated from 27°C to 927°C. then the ratio of radiation emitted will be (MHT-CET-2005) (a) 1: 4 (b) 1: 16 (c) 1: 8 (d) 1: 256 Answer: (d) 10 You are given a sphere, a cube and a thin circular plate, all made from copper and all having the same mass. If they are heated to a temperature of 200°C, then which are of them will cool fasted? (a) Sphere (b) Thin circular plate (c) Cube (d) All at the same rate Answer: (b) 11 For a given body at a particular temperature, its coefficients of reflection and transmission are 0.63 and 0.21 respectively. Then its coefficient of emission at the same temperature will be (a) 0.16 (b) 0.32 (c) 0.84 (d) 0.36 Answer: (a) 12 The unit of Stefa’s constant is (MHT-CET-2006) (a) watt/m2 K4 (b) watt/m3 K (c) watt/m2 K (d) watt/m3 K4 Answer: (a) 13 A body of surface area 25 × 10–3 m2 emits 0.4 Kcal of heat in 20 s at 50°C. What is the emissive power of the body at that temperature? (a) 0.5 Kcal/m2/S (b) 0.6 Kcal/m2/S (c) 0.7 Kcal/m2/S (d) 0.8 Kcal/m2/S Answer: (d) 14 The wavelength of maximum energy release during an atomic explosion was 2.93 × 10–10 m. the maximum temperature attained must be (Wein’s constant = 2.93 × 10–3 mK) (MHT-CET-2002) (a) 5.86 × 107 K (b) 10–13 k (c) 10–7 K (d) 107 K Answer: (d) 15 The solar constant for the earth is about 1.8 J/m2/S. what is the solar constant for a black body situated on a planet which is situated at a distance of 0.3 times the distance of the earth from the sun? (a) 9 J/m2/S (b) 12 J/m2/S (c) 15 J/m2/S (d) 20 J/m2/S Answer: (d) 16 Emissivity of perfectly black body is (MHT-CET-2003) (a) 1 (b) 2 (c) 5 (d) 0 Answer: (a) 17 The velocity of thermal radiation (V) is related to the velocity of light (C) as (a) V > C (b) V < C (c) (d) V = C Answer: (d) 18 If a = 0.72, r = 0.24, then value of t is (MHT-CET-2003) (a) 0.02 (b) 0.04 (c) 0.4 (d) 0.2 Answer: (b) 19 Wien’s constant units is (MHT-CET-2008) (a) m.k (b) kg (c) m.m (d) mg. Answer: (a) 20 A liquid takes 5 minutes to cool from 80°C to 50°C. how much time it will take to cool from 60°C to 30°C, if the temperature of the surrounding is 20°C? (a) 5 minutes (b) 7 minutes (c) 9 minutes (d) 12 minutes Answer: (c)