Physics Objective Test No.19


   Multiple Choice Questions
1. The earth receives at its surface radiation from the sun at the rate of 1400 W/m2. the distance of
the centre of the sun from the surface of the earth is 1.5 ´ 1011 m and the radius of the sun 
is 7.0 ´ 108 m. treating sun as a black body, it follows from the above data that its surface
temperature is,
a) 5801 K
b) 106 K
c) 50.1 K
d) 2801°C
Answer
2. The process of heat transfer in which heat is transferred with actual migration of medium 
particles is known as
a) Conduction
b) Convection
c) Radiation
d) Reflection
Answer
3. A black body is at a temperature of 500 K. It emits energy at a rate which is proportional to
a) 500
b) (500)2
c) (500)3
d) (500)4
Answer
4. Which of the following is most repaid process
a) Conduction
b) Convection
c) Radiation
d) None of these
Answer
5. The wavelength of maximum energy released during an atomic explosion was 2.93 ´ 10-10m.
 the maximum temperature attained must be (Wien’s constant = 2.93 ´ 10-3mK) 
a) 5.86 ´ 107 K
b) 10-13 K
c) 10-7 K
d) 107 K
Answer
6. If a = 0.72, r = 0.24, then the value of t is
a) 0.02
b) 0.04
c) 0.4
d) 0.2
Answer
7. A body cools from 50°C to 46°C in 5 minutes and to 40°C in the next 10 minutes. The 
surrounding temperature is
a) 30°C
b) 28°C
c) 36°C
d) 32°C
Answer
8. According to Wien’s law
a) λm T = constant
b) λm/T = constant
c) T/λm  =constant
d) T + λm  = constant
Answer
9. A black body is at 300 K. it emits energy at a rate which is proportional to
a) (300)
b) (300)2
c) (300)4
d) (300)3
Answer
10. Which of the following will radiate heat to large extent?
a) Rough surface
b) Polished surface
c) Black rough surface
d) Black polished surface
Answer

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