Notes on Wave Optics

🔰Notes on Wave Optics

Magnifying power or magnification of a simple microscope:- M= 1+(D/f)

Magnifying power or magnification of a compound microscope:-

M= L/f0 (1+D/fe)

Here, f0 is the focal length of the objective, fe is the focal length of the eyepiece and L is the length of the microscope tube.

Magnification of astronomical telescope in normal adjustment:-

M = f0/fe

Magnification of astronomical telescope, when the final image is formed at the distance of distinct vision:-

M = (f0/fe) [(fe+D)/D]

Magnifying power M of Galileo’s telescope:-

M = focal length of objective/focal length of eye lens = F/f

Diffraction:- Diffraction is the bending  or spreading of waves that encounter an object ( a barrier or an opening) in their path.

(a) In Fresnel class of diffraction, the source and/or screen are at a finite distance from the aperture.

(b) In Fraunhofer class of diffraction, the source and screen are at infinite distance from the diffracting aperture. Fraunhofer is a special case of Fresnel diffraction.

If Im represents the intensity at O, its value at P is

Iθ = Im (sinα/α)2

Here, α = ?/2 = πa sinθ/λ

A minimum occurs when, sin α = 0 and α is not equal to zero.

so  α = nπ,       n = 1, 2, 3...

So, πa sinθ/λ = nπ

Or, a sinθ = nλ

Angular width of central maxima of diffraction pattern = 2θ1 = 2 sin-1(λ/a)

[ θ1 gives the angular position of first minima]

Polarization: - Polarization of two interfering wave must be same state of polarization or two source of light should be un polarized.

Brewster Law:-

According to this law when un polarized light is incident at polarizing angle (i) on an interface separating a rarer medium from a denser medium, of refractive index m as shown in Fig., below such that,

 µ = tan i

Then light reflected in the rarer medium is completely polarized. Reflected and refractive rays are perpendicular to each other.

Reduction in Intensity:- Intensity of polarized light is 50% of that of the un polarized light, i.e.,

 Ip = Iu/2

Here, Ip = Intensity of polarized light.

Iu = Intensity of un polarized light.