A heat lamp emits infrared radiation whose rms electric field is E_rms = 3080 N/

Question

A heat lamp emits infrared radiation whose rms electric field is E_rms = 3080 N/C. (a) What is the average intensity of the radiation? (b) The radiation is focused on a person's leg over a circular area of radius 4.4 cm. What is the average power delivered to the leg? (c) The portion of the leg being radiated has a mass of 0.26 kg and a specific heat capacity of 3500 J/(kg middot C degree). How long does it take to raise its temperature by 2.1 C degree? Assume that there is no other heat transfer into or out of the portion of the leg being heated.

Explanation / Answer

a)

we know that intensity

I = E^2 / 2uc

where E is maximum Electric field

E = Erms ( 1.414)

so

I = 3.97 x 10^-8 W/m^2

b)

P = I x area

P = 2.41682 x 10^-10 W

c)

P x time = M s ( delta T)

P t = 0.26 x 3500x2.1

t = 7.9 x 10^12 s

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