PH113
Solution to Quiz 7

Tuesday 4/26/16	Name
O205: periods 1, 2
	CM #

An intense lightsource (point) radiates uniformly in all directions.A detector is placed 5.00 m from the source. The radiation pressure measured by the detector is 9.00×10^-6 Pa. Assume that the surface is perfectly absorbing and that the radiation is incident normally.

c=3.00×108 m/s eo=8.85×10-12 C/V·m

I=eocE2o/2 prad=I/c prad=2I/c I=P/A

(a) Calculate the intensity of the radiation falling on the detector.



I=pradc=(9.00×10-6 Pa)(3.00×108  m/s)=2700 W/m2


(b) Calculate the electric field amplitude of the radiation at the detector.


Eo = æ è 2I ceo ö ø 1/2   = é ë 2(2700 W/m2) (8.85×10-12  C/V·m)(3.00×108 m/s) ù û 1/2   = 1426 V/m ® 1430 V/m


(c) Calculate the average power delivered by the source.



Pav=IA=I(4pr2)=4p(2700 W/m2) (5.00 m)2=8.48×105 W

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On 27 Apr 2016, 10:37.