Question

Three discs, A, B and C having radii 2 m, 4 m and 6 m respectively are coated with carbon black on their outer surfaces. The wavelengths corresponding to maximum intensity are 300 nm, 400 nm and 500 nm, respectively. The power radiated by them are QA, QB and QC respectively

Answer 1

according to Wein's displacement:

law λT = constant

so ratio of temperatures of the three discs will be 1/3:1/4:1/5 = 20:15:12

and ratio of area of the discs = 1:4:9

now according to Stephan's law Q α  A × T4

so ratio Qa:Qb:Qc = 1×(20)4 : 4×(15)4 : 9×(12)4

on solving we will get that Qb is maximum.

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