Question

a) A soap film appears invisible when it approaches a zero-thickness.
In 50 words and/or a figure, explain why.
[1] b) The north pole attracts the south pole of a compass needle allowing navigation. T/F
[1] c) There are 3 colour sensors in the eye with maximum responsivity centered on the
primary colours red, yellow and blue. T/F
[1] d) A “red/green colour blind” person is able to detect only red or green light, not the
other. T/F
[2] e) Unpolarized white light is incident on a glass plate at Brewster’s angle. Some of the
light is reflected, some is transmitted. Describe the polarization and colour of the reflected beam
using 50 words and/or a figure.
[2] f) Describe the polarization and colour of the transmitted beam using 50 words and/or a
figure.

Answer 1

(A) when light passes through a soap film the light undergoes thin-film interference. interference effects are most prominent when light interacts with something having a size similar to its wavelength. As we reduce the thickness below 380nm the light (visible light wavelength lies b/w 380-740nm ) no longer interact with the soap bubble so it will appear to our human eye as invisible.

(B) true, that's how all the compasses work, the north pole of the earth attracts the south pole of the needle and vice versa

(C)False, the three colour receptors in our eyes are RED, GREEN and BLUE called the trichromats, these colours are called the primary colours

(D)false, Color blindness occurs when you are unable to see colours in a normal way. Colour blindness can happen when one or more of the colour cone cells are absent, not working, or detect a different colour than normal. So if someone is red colour blind is will not be able to detect red colour.

(E)

the reflected light becomes completely polarized when the angle of incidence is called the Brewster angle.the reflected light will be polarised perpendicular to the plane of the paper, and the light will still be white because all the colours will get polarized independent of the wavelength. reflected will only have s-component

(F) The transmitted beam has both components and hence is never completely polarized. However, at the Brewster angle, all of the p component is transmitted (no reflection) and only a part of the s component is transmitted (the rest is reflected) - so the transmitted light is partially p polarized(polarised parallel to the plane of the paper), the light will still be white.