(a) What is the intensity in W/m 2 of a laser beam used to burn away cancerous t

Question

(a) What is the intensity in W/m2 of a laser beam used to burn away cancerous tissue that, when 90.0% absorbed, puts 480 J of energy into a circular spot 2.00 mm in diameter in 4.00 s?      (b) Compare this intensity to the average intensity of sunlight (about 1 kW/m2).
(intensity of laser / avg intensity of sunlight) =                                                                                                                                                                                                                                            

Explanation / Answer

here,

diameter of circular spot , d = 2mm

radius of circular spot , r = 1 mm

r = 0.001 m

initial power of the laser beam , P = 480 / (4 * 0.9)

P = 133.33 W

intensity of the laser beam , I = power / area

I = 133.33 / pi * r^2

I = 133.33 / pi * (0.001)^2

I = 42.46 * 10^6 W/m^2

intensity of the laser beam is 42.46 * 10^6 W/m^2

(b)

ratio of intensity to the average intensity of sunlight = intensity of laser / avg intensity of sunlight

ratio of intensity to the average intensity of sunlight = 42.46 * 10^6 / (10^3)

ratio of intensity to the average intensity of sunlight = 42.46 * 10^3

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