Assume the mostly infrared radiation from a heat lamp acts like a continuous wav

Question

Assume the mostly infrared radiation from a heat lamp acts like a continuous wave with wavelength 1.50 µm. (a) If the lamp's 215 W output is focused on a person's shoulder, over a circular area 26.0 cm in diameter, what is the intensity in W/m2? W/m2 (b) What is the peak electric field strength in kV/m? kV/m (c) Find the peak magnetic field strength in µT. µT (d) How long will it take in seconds to increase the temperature of the 4.05 kg shoulder by 2.00°C, assuming no other heat transfer and given its specific heat is 3.47 ? 103 J/(kg · °C)? s

Explanation / Answer

a)

Intensity

I=P/A =215/(pi*0.262/4) =4049.5 W/m2

b)

SInce

I=(1/2)CeoE2

4049.5 =(1/2)(3*108)(8.8542*10-12)E2

E=1746.15 V/m =1.746 KV/m

c)

B=E/C =1746.15/(3*108)

B=5.82 uT

d)

Heat energy requires

Q=mcdT

and SInce Q=Pt

=>t =mcdT/P =4.05*3470*2/215

t=130.73 s

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