## two optic problem

kolndom
Posts: 19
Joined: Tue Oct 25, 2005 11:29 am

### two optic problem

In the first problem, I do not know why C is right. would some one help me out? thank u in ad:)
*Op20. A ray of unpolarized monochromatic light traveling in vacuum is incident on a flat plate of glass at an angle equal to Brewster’s angle (57 for this case), as shown above. Which of the following statements is NOT correct?
(A)The tangent of the angle of incidence is equal to the index of refraction of the glass plate.
(B)The angle between the reflected ray and the refracted ray is 90.
(C)The refracted ray is partially plane polarized. ?????
(D)The reflected ray is 100% linearly polarized.
(E)The plane of vibration of the electric vector in the reflected ray is parallel to the plane of incidence of the light ray.

I do not know who to solve the second problem at all! Would some one help me? thank u in ad:)
*Op7 Light of wavelength 5200 Angstroms is incident normally on a transmission diffraction grating with 2000 lines per centimeter. If the width of one slit is reduced to , what happens to the interference pattern of the light from the two slits?
(A)It remains the same except that it has lower intensity.
(B)It remains the same except that it is replaced.
(C)It still has intensity I0 at angle= 0.
(D)It no longer has minima with zero intensity.
(E) It has zero intensity at angle= 0.

danty
Posts: 19
Joined: Fri Sep 30, 2005 6:40 pm
Fist Problem

It seems to me, that E is not the correct satement. In incidence with a brewster angle, the plane of vibration of the electric field in the reflected ray is normal , not parallel, to the plane of incidence of the ray.

It is true that the refracted ray is partially plane polarazided, so C statement is correct.

sciencexgirl
Posts: 14
Joined: Mon Nov 07, 2005 9:15 pm

### Diffraction grating or two slits?

I'm confused about the actual question where the width of a slit gets changed. A diffraction grating and a double slit are not exactly the same thing, because with a diffraction grating there are many slits, as I remember. Where are you getting these problems?

I'm going to assume that you mean a double-slit setup, and that the "width of one slit is reduced to" .... what? well, if you reduce it until it is lower than the wavelength of the light going through the apparatus, then there is no transmission through the slit, and it becomes a single-slit experiment. If not, you can solve the problem rigorously using a method of fourier transformations found in most math for physicists textbooks.

Also,
B doesnt make any sense unless "replaced" is replaced with "displaced".

sciencexgirl
Posts: 14
Joined: Mon Nov 07, 2005 9:15 pm
possible correction-you should check on this- but it might be that light fails to transmit trough a slit if the slit width is less than HALF a wavelength, rather than a wavelength, as i originally stated.