Question

1. The emissive power of a sphere of area
0.02 mºis 0.5 kcal s'm? What is the
amount of heat radiated by the spherical
surface in 20 second?
Ans. 0.2 kcall​

Answer 1

Emissive power = E = 0.5kcal/m²s

Area = 0.02m²

Time = 20 sec

We need to calculate the amount of heat

Using formula of emissive power

E = Q/At

Q = EAt

Where, E = emissive power

A = area

t = time

Put the value into the formula

Q  = 0.5×10³×0.02×20

Q = 200 cal

Q = 200×4.184J

Q = 836.8 J

Hence, The amount of heat is 836.8 J.

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