XII wave optics
1. In
Young’s double-slit experiment, the intensity of light at a point on the
screen, where the path difference is l , is K units. What is the intensity at
a point where the path difference is: (a) l / 2 and (b) l / 3?
{Ans. (a) 0, (b) k / 4}
2. A
glass slab of thickness 8 cm contains the same number of waves as 9 cm of water
when both are traversed by the same monochromatic light.If refractive index of
water is 4 / 3, calculate the refractive index of glass.
(Ans. 1.5)
3. In
Young’s double slit experiment, while using a source of light of wave length
5000 Å, the fringe width obtained is 0.6 cm. If the distance between the slits
and the screen is reduced to half, calculate the new fringe width.
(Ans. 3 mm)
4. In
a Young’s double slit experiment the distance between the slits and screen is 1
m. If the distance between the slits is 5 mm, the fringe width is found to be
0.1 mm. Calculate the wavelength of light used.
(Ans. 5000 Å)
5. In Young’s double slit experiment, while using a source of
light of wave length 5000 Å, the fringe width obtained is 0.6 cm. If the
distance between the slits and the screen is reduced to half, calculate the new
fringe width.
(Ans. 3 mm)
6. Red
light of wave length 6500 Å from a distant source falls on a slit 0.50 mm wide.
What is the distance between the two dark bands on each side of the central
bright band of diffraction pattern observed on a screen placed 1.8 from the
slit?
(Ans. 4.58 mm)
7. A
slit of width ‘a’ is illuminated by light of wavelength 6000 Å. For what value
of ‘a’ will be (i) first maximum fall at an angle of diffraction of 30º? (ii)
first minimum fall at an angle of diffraction of 30º?
{Ans. (i) 3.6 ´ 10–6 m (ii) 1.2 ´
10–6 m}
8. A
beam of polarised light makes an angle of 60º with the axis of the polaroid
sheet. How much is the intensity of light transmitted through the sheet?
(Ans. 25%)
9. A
ray of light strikes a glass plate at an angle of 60º with the glass surface. If
the reflected and refracted rays are at right angles to each other, find the
refractive index of the glass.
(Ans. 1.732)
10. A beam of
light of wavelength 600 nm from a distant source falls on a single slit 1 mm
wide and resulting diffraction pattern is observed on a screen 2m away. What is
the distance between the first dark fringes on either side of the central
bright fringe.
(Ans. 2.4 mm)
11. Limits
of the visible spectrum are 4000Å to 7000 Å. Show that the violet of 3rd order
visible spectrum overlaps the red of the second order spectrum, produced by a
plane grating having 15000 line / inch, when the light is incident normally on
the grating.
(Ans. 45.14º)
12. A
polaroid is placed at 45º to an incoming light of intensity I0 . Find the intensity
of light passing through polaroid after polarisation.
(Ans. I0 / 2)
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