A low-power laser used in a physics lab might have a power of 0.40 mW and a beam

Question

A low-power laser used in a physics lab might have a power of 0.40 mW and a beam diameter of 2.6 mm.

(a) Calculate the average light intensity of the laser beam.

=75.34 W/m^2

(b) Compare it to the intensity of a light bulb producing 60 W light viewed from 2.0 m (I laser/ I bulb)

=?

I have the answer of (a), but I just need help on the answer of (b). I calculated (b) using I=P/A => I=[(60 W)/(pi*(2 m/2)^2))]= 19.099 W/m^2. Then I divided that by my answer from (a) (aka (75.34 W/m^2)/(19.099 W/m^2)= 3.945), and the answer was incorrect. I'm just not sure what I'm doing wrong.

Explanation / Answer

intensity= power/ area= 0.40*10^-3/(pi/4*(2.6*10^-3)^2)= 75.34 W/m^2

2nd intensity= 60/( pi/4*2^2)= 19.09

I laser/I bulb= 75.34/19.09= 3.945

you are correct

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