File Edit View Insert FormatArrangeTools Slide Show Recovered File 1 69% 58 Tabl

Question

File Edit View Insert FormatArrangeTools Slide Show Recovered File 1 69% 58 Tables Charts SmartArtT Example Problem A small LED (light-emitting diode) emits 58.9 W of unpolarized 650 nm electromagnetic radiation. A small circular detector (with a radius of 1.0 cm) is then placed at 5.0 m from this LED. A. What is the intensity of the light at the detector? B. What is the rms field strength of the magnetic component of the wave at the detector? C. How much energy from the EM wave is incident on this detector in a time of 2.0 s? Side 25-43 Study for the quiz Slide 43 of 64 69% -o

Explanation / Answer

(A) I = P / (4 pi r^2)

I = (58.9 W) / (4 pi (5m)^2)

I = 0.187 W/m^2

(B) I = c B_rms^2 / u0  

0.187 = (3 x 10^8) (B_rms)^2 / (4 pi x 10^-7)

B_rms = 2.80 x 10^-8 T  

(C) P_incident = I A = I (pi r^2)

= (0.187) (pi (0.01^2))

= 5.89 x 10^-5 W

energy indicent = P t

= (5.89 x 10^-5)(2s)

= 0.118 x 10^-3 J

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