Optical tweezers use light from a laser to move single atoms and molecules aroun

Question

Optical tweezers use light from a laser to move single atoms and molecules around. Suppose the intensity of light from the tweezers is 1000 W/m2, the same as the intensity of sunlight at the surface of the Earth. (a) What is the pressure on an atom if light from the tweezers is totally absorbed? Pa (b) If this pressure were exerted on a helium atom, what would be its acceleration? (The mass of a helium atom is 6.65 1027 kg. Assume the cross-sectional area of the laser beam is 6.65 1029 m2.) m/s2

Explanation / Answer

From the given question,

a)Intensity of light(E)=1000 W/m2

speed of light(c)= 3 x 108 m/s

radiation pressure exerted by an electromagnetic wave on the surface of a target is given by

p=E/c=1000 /(3 x 108 )=3.33 x 10-6 pascals

pressure on atom is 3.33 x 10-6 pascals

b)mass of a helium atom(m)= 6.65 1027 kg

cross-sectional area of the laser beam (A)=6.65 1029 m2.

Force = pressure x cross sectional area

=3.33 x 10-6 x 6.65 1029

=2.21 x 10-34 N

Force = mass x acceleration

2.21 x 10-34 = 6.65 1027 x a

a = 3.32 x 10-8 m/s2

The acceleration on helium atom will be 3.32 x 10-8 m/s2

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