H1. The rate at which the radient energy reaches the surface from the sun is about 1.4 kw/m2. The distance from the earth to the sun is about 1.5 x 1011 and the radius of sun is about 0.7 x 109m
(a) What is the rate radiation of energy, per unit area from the sun’s surface?
(b) What is the temperature of sun’s surface assuming it to be a black body?
Solution: (a) The energy crossing through a unit area per second
= D: Distance between sun and earth.
= 1.4 x 103
P = 3.96 x 1026
= 6.43 x 107 wm-2
(b) = 1
E = T4
T = = 5803 K
H2: A 2m long wire of resistance 4 ohm and diameter 0.64 is coated with plastic insulation of thickness 0.06mm. when a current of 5a flows through the wire, find the temperature difference across the insulation in steady state if K = 0.16 x 10-2 cal/cm 0c see.
Solution: H =
H = -
Q1 - Q2 = 20 c
H3: Consider a spherical black body for the body to cool down from 1000k to 300 K ? Density of Cu = a x 103 kg/m3 and specific heat = 4 KJ/kg.
Solution: = AT4
|t = 127 x 103 sec|
(4) Absorptive Power(a)
(5) Emmissive Power(e)
(7) Black Body