A 0.57 mW laser produces a beam of lightwith a diameter of 1.5 mm. (a) What is t

Question

A 0.57 mW laser produces a beam of lightwith a diameter of 1.5 mm. (a) What is the average intensity of thisbeam?
1 W/m2
(b) At what distance does a 150 W light bulb have the same averageintensity as that found for the laser beam in part (a)? (Assumethat 5.0% of the bulb's power is converted to light.)
2 cm (a) What is the average intensity of thisbeam?
1 W/m2
(b) At what distance does a 150 W light bulb have the same averageintensity as that found for the laser beam in part (a)? (Assumethat 5.0% of the bulb's power is converted to light.)
2 cm

Explanation / Answer

we have average power Pav = 0.57*10-3W diameter of the beam of light d = 1.5mm radius of the beam of light r = 0.75mm                                            =0.75*10-3m a) average intensity of the beam Iav =Pav/A                                                    = Pav/r2                                                    = -------------- b) average power of the light bulb Pbulb = 150W distance at which the light bulb of 150W has the sameintensity is given by                    Pbulb / 4d2 =Plaser/r2 where 4d2 is the surface area of thebulb , from equation (1) we can write as      the distance d =r/2*(Pbulb/Plaser)                            = r/2*(150W*0.050/Plaser)                             = --------------

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