A heat lamp emits infrared radiation whose rms electric field is E rms = 3052 N/
ID: 1431914 • Letter: A
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