A 23.6-mW laser beam of diameter 2.17 mm is reflected at normal incidence by a perfectly reflecting mirror. Calculate the radiation pressure on the mirror.

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+3 votes

Best answer

Note: I solved this by looking at units and the answer key on another version

Take the diameter (d) and divide it by 2 to find the radius (r). Then find area (pi*r^2). So:

(d/2)^2*pi=A

The laser beam is in mW (miliWatts), so divide by 1000 to get it into Watts. Force times velocity is equal to power. So:

F*v=P becomes

F=P/V where P is your Watts and v is speed of light (3*10^8)

2*(F/A)=radiation pressure

Take the diameter (d) and divide it by 2 to find the radius (r). Then find area (pi*r^2). So:

(d/2)^2*pi=A

The laser beam is in mW (miliWatts), so divide by 1000 to get it into Watts. Force times velocity is equal to power. So:

F*v=P becomes

F=P/V where P is your Watts and v is speed of light (3*10^8)

2*(F/A)=radiation pressure

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