Assume the helium-neon lasers commonly used in student physics laboratories have power outputs of 0.250 mW. (a) If such a laser beam is projected onto a circular spot 3.00 mm in diameter, what is its intensity (in watts per meter squared)

35.4watts/m²

Explanation:

Given the power output of helium-neon laser = 0.250mW = 0.250×10^-3watts (1milliwatts = 10^-3watts

Diameter of the circular spot projected by laser beam = 3.00mm = 0.003m

Area of the circular spot = πd²/4

Area of the circular spot = π(0.003)²/4

= 7.069×10^-6m²

Intensity of the laser = power output/area

Intensity of laser = 0.250×10^-3Watts/7.069×10^-6m²

= 0.0354×10^-3+6

= 0.0354×10^3

Intensity of laser = 35.4watts/m²

power out to power in less than 100%

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