A heat lamp emits infrared radiation whose rms electric field is E rms = 3052 N/

Question

A heat lamp emits infrared radiation whose rms electric field is Erms = 3052 N/C.

(a) What is the average intensity of the radiation?
______W/m2

(b) The radiation is focused on a person's leg over a circular area of radius 3.6 cm. What is the average power delivered to the leg?
________W

(c) The portion of the leg being radiated has a mass of 0.27 kg and a specific heat capacity of 3500 J/(kg · C°).How long does it take to raise its temperature by 2.2 C°? Assume that there is no other heat transfer into or out of the portion of the leg being heated.

_____s

Explanation / Answer

Formula for average intensity is

I  =   c o Erms2 = 3 x 108* 8.85 x 10-12* (3052)^2 = 2.47x 104W /m2

formula for average power is

                P = I A

=  2.47 x104 W / m2  * ( pi * r2 )

                                =   2.47 x 104 * 3.14 * ( 3.6x 10-2)2

                                = 1.00 x 102 W

(c)

P = Q/t = mc del T/ t

t =  mc del T/ P

=( 0.27 kg * 3500 * 2.2 ) /100 W

                 = 20.79 s

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