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 tritium atom, what would be its acceleration? (the mass of a tritium atom is 5.01 ✕ 10−27 kg. assume the cross-sectional area of the laser beam is 6.65 ✕ 10−29 m2.)

(a)  

The radiation pressure exerted by an electromagnetic wave on a surface that totally absorbs the radiation is given by

where

I is the intensity of the wave

c is the speed of light

In this problem,

and substituting , we find the radiation pressure

(b)

Since we know the cross-sectional area of the laser beam:

starting from the radiation pressure found at point (a), we can calculate the force exerted on a tritium atom:

And then, since we know the mass of the atom

we can find the acceleration, by using Newton's second law:

scattering of light by tiny particles in air to produce the colors we see on sky, is dependent on the following factors:

(i) wavelength of light

(ii) size of the scattering particle  

(iii) distance traveled by light through the atmosphere.

according to rayleigh's law of scattering, the amount of scattering is inversely proportional to the fourth power of its wavelength. shorter the wavelength, greater is its scattering. hence violet/blue light is scattered more than red.

sun's light is a composite light ( visible light) with wavelengths in the range 400 nm (violet) to 700 nm (red). as sunlight passes through our atmosphere, the molecules of air scatter light according to their wavelengths. during sunrise and sunset, the sun's position is below the horizon. hence light from the sun travels a greater distance in the atmosphere when compared to its position a noon.

as sunlight enters the earth's atmosphere, blue light is scattered away and at the end of its journey in the sky, only red and orange wavelengths remain in the beam.

hence at sunrise and sunset, the sky appears reddish orange.

not too sure thinking all accelerations are pointed down