Explain the questions clearly. For Q.1 and 2, please also explain the wrong options.
1. When a beam of unpolarized light travelling in air falls on a water surface, it is possible to find an angle of incidence such that
(1) all the light is reflected
(2) the light passing into water is plane polarised
(3) the reflected light is plane polarized
2.Light of wavelength 500nm is incident normally on a plane diffraction grating having a ruling of 5000 lines per cm. Which of the following descriptions is/are correct?
(1) The spacing between the rulings is 2000nm
(2) The angle through which the second-order spectrum diffracted is 30
(3) No third-order spectrum is observable.
3. The intensity of solar radiation falling normally on the earth's surface due to the overhead sun is about 500Wm^-2. It is known that about 2/3 of the solar radiation reaching the earth is absorbed by the atmosphere. Estimate the total power output of the sun. (Given: earth-sun separation = 1.5 *10^8 km)
4. A diver at a depth of x below the water surface looks up and finds that the sky appears to be within a circle of radius r. The critical angle of water in this case in given by
A. tan^-1(r/x) B. sin^-1(r/x) C. tan^-1(x/r) D. sin^-1(x/r)
5. In a Young's double silt experiment using monochromatic light of wavelength 550nm, the fringes are observed through the eyepiece of a travelling microscope at a distance of 1.0 m from the double silts. If the separation between the first and the fifth dark fringes. Find the silt separation.
5 short questions
2010-01-10 8:00 pm
回答 (1)
2010-01-11 10:43 pm
✔ 最佳答案
1. Statement (3) is correct.2. Statments(1) and (2) are correct
ruling spacing = 1/5000 cm = 1/5000 x 10^7 nm = 2000 nm
angle of diffraction for 2nd order spectrum = arc-sin[2 x 500/2000]
3. Radiation before entering into atmosphere = 500 x 3 W/m2 = 1500 W/m2
Hence total power given out = 1500 x [4 x pi x (1.5x10^11)^2] w = 4.24x10^26 watts
[pi =3.14159...]
4. From simple trigonometry, tan(c) = r/x
c = arc-tan[r/x]
5. For destructive interference to occur
a.sin(theta) = (m-0.5)w
where a is the slit separation, w is the wavelength of light used, [theta] is the angular position of the dark fringe with order m
since [theta] is usually small, sin(theta) = tan(theta) = y(m)/D
where y(m) is the separation between the central bright fringe and the m(th) order dark fringe, D is the screen-slit spearation
hence, a.[y(m)/D] = (m-0.5)w
y(m) = (m-0.5)wD/a
therefore, y(5)-y(1) = (4.5-0.5)wD/a = 4wD/a
i.e. a = 4wD/[y(5)-y(1)]
收錄日期: 2021-04-29 17:33:25
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