Download GGN PUBLIC SCHOOL, LUDHIANA XII PHYSICS ASSIGNMENT

GGN PUBLIC SCHOOL, LUDHIANA
XII PHYSICS ASSIGNMENT
(OPTICS)
Very short answer questions (1 mark)
1. Define one lumen.
2. How does the focal length of convex lens change if monochromatic red light is used instead of monochromatic
blue light?
3. A convex lens is immersed in a medium of refractive index μL, immersed in a medium of refractive index μM . How
will the lens behave when μL >μM.
4. A diverging lens of focal length f is cut into two identical parts each forming a plano-concave lens. What is the
focal length of each part?
5. Why the scratches on the lens of a photographic camera do not appear on the photograph?
6. What happens to the focal length of a convex lens when it is immersed in water?
7. Refractive indices of glass for light of yellow, green and red colors are μY, μG, and μR respectively. Rearrange these
symbols in decreasing order of values.
8. How the power of convex lens vary when, if the incident red light is replaced by violet light.
9. When light travels from a rarer medium to a denser medium, its speed decreases. Does this increase in speed
imply a decrease in the energy carried by the light wave?
10. When does a convex lens behave as a concave lens?
11. What type of lens is an air bubble inside water? Give reason also.
12. A convex lens placed in a medium behaves as an ordinary plate. What is the refractive index of the medium
relative to the lens?
13. A lens immersed in a transparent liquid is not visible. Under what condition can this happen?
14. A lens whose radii of curvature are different is forming the image of an object placed on its axis. If the lens is
placed with its faces reversed, will the position of the image change?
15. Sun glasses (goggles) have curved surfaces but they do not have any power. Why?
16. What is lens maker’s formula? Why is it so called?
17. Define critical angle w.r.t. total internal reflection. Calculate the critical angle for glass air surface if a ray of light
which is incident in air on a glass surface is deviated through 15° when the angle of incidence is 45°. [45°]
18. What is the relation of a wave front with a ray of light?
19. Does interference phenomenon reveal the nature of light waves?
20. Why do two identical bulbs do not produce interference?
21. Doppler shift due to motion of light source or observer with same velocity is identical. This is not for
second source. Why?
22. Why can light waves be polarized but sound waves cannot?
23. Why is sun glasses made of Polaroid’s superior than those using coloured glasses?
24. Sketch the wave front emerging from a point source of light and linear source of light like a slit.
25. State Huygens’s principle.
26. Two coherent sources of intensity ration 4: 1 interfere. Obtain the ration of intensity between the maxima
and minima in the interference pattern.
27. The refractive index of a medium is √3. What is the angle of refraction, if the unpolarized light is incident
on it at the polarizing angle of the medium?
28. What is the polarizing angle of a medium of refractive index 1.732?
29. Why is diffraction pattern invisible when the slit is very wide?
30. Why is coloured spectrum seen when we look through a muslin cloth?
Short answer questions (2 or 3 marks)
1. What is a light pipe?
2. What is zoom lens?
3. What is spherical aberration? How it is different from chromatic aberration? Will the reflected rays converge at a
point when a parallel beam of light is incident on a concave mirror of large aperture? Give two methods to get a
clear focusing of the image on the screen without disturbing the position of the object.
4. State the conditions for the Total Internal Reflection takes place? Derive the relation for the critical angle in
terms of the speed of light in the respective media.
5. What are optical fibres? How do optical fibres transmit light without significant absorption? Discuss its one use.
6. Violet light is incident on a converging lens of focal length f. State, with reason, how the focal length of the lens
will change, if violet light is replaced by red light? (decrease)
7. Explain why white light is dispersed when passing though a prism.
8. Draw a well labeled diagram to show image formation in an astronomical telescope for a distant object in (i) near
point adjustment.(ii) normal adjustment position
9. Give reasons for the following observations for the made from the earth: (a) sun is visible before the actual
sunrise (b) sun looks reddish at sunset.
10. Draw a graph showing the variation of angle of deviation D with that of angle of incidence I for a monochromatic
ray of light passing through a glass prism of refracting angle A. hence deduce the prism formula.
11. Draw a plot showing variation of power of a lens, with the wavelength of the incident light. A converging lens of
refractive index 1.5 and of focal length 15cm in air has the same radii for curvature for both sides. If it is
immersed in a liquid of refractive index 1.7, find the focal length of the lens in the liquid. [63.75 cm]
12. If white light is used in Young’s experiment, what kind of pattern will be observed?
13. Using Huygens’s principle, draw a diagram to show propagation of a wave front originating from a
monochromatic point source.
14. Using Huygens’s principle, derive Snell’s law
15. How are Polaroids artificially made? Mention two uses of Polaroids. Draw a graph showing the dependence
of intensity of transmitted light on the angle between polarizes & analyzer.
16. In a single slit diffraction pattern, how does the angular width of the central maximum vary, when (i)
aperture of slit is increased (ii) distance between the slit and screen is decreased (iii) monochromatic visible
light of larger wavelength is used? Justify your answer in each case.
Numericals
1. The radius of curvature of each face of biconcave lens, made up of glass of refractive index 1.5 is 30 cm.
calculate the focal length of the lens in air. [-30cm]
2. The radius of curvature of the faces of a double concave lens are 10cm and 15 cm. if focal length is 12 cm, what
is the refractive index of the glass?[1.5]
3. A biconvex lens has a focal length half the radius of curvature of either surface. What is the refractive index of
lens material? [2]
4. The radii of curvature of a double convex lens of glass (μ=1.5) are in the ratio 1:2. This lens renders the rays
parallel coming from an illuminated filament at a distance of 6 cm. Calculate the radii of curvature of its
surfaces. [+4.5cm, -9cm]
5. A converging lens has a focal length of 20 cm in air. It is made of a material of refractive index 1.6. if it is
immersed in a liquid of refractive index 1.3, what will be the new focal length?
6. Find the radius of curvature of the convex surface of a plano-convex lens, whose focal length is 0.3m and the
refractive index of the material of the lens, is 1.5. [0.15 m]
7. A convex lens of focal length 0.2m and made of glass (μ=1.5) is immersed in water (μ=1.33). Find the change in
the focal length of the lens. [0.58 m]
8. The radii of curvature of double convex lens are 10 cm and 20 cm respectively. Calculate its focal length when it
is immersed in a liquid of refractive index 1.65. State the nature of the lens in the liquid. The refractive index of
glass is 1.5. [-73.33 cm]
9. If the refractive index from air to glass is 3/2 and that from air to water is 4/3, find the ratio of focal lengths of a
glass lens in water and in air. [4:1]
10. A double convex lens has a focal length of 25 cm in air. When it is dipped into a liquid of refractive index 4/3, its
focal length is increased to 100 cm. Find the refractive index of the materials used. [1.5]
11. The focal lengths of the eyepiece and the objective of a compound microscope are 5cm and 1 cm, respectively
and the length of the tube is 20 cm. Calculate the magnifying power of the microscope, when the final image is
formed at infinity. The value of least distance of distinct vision is 25cm.[70]
12. Draw a well labeled diagram of a compound microscope, showing the formation of image at the near point of
the eye. (ii) A compound microscope uses an objective lens of focal length 4 cm and eye lens of focal length
10cm. An object is placed at 6 cm from the objective lens. (a) Calculate magnifying power of the compound
microscope, if the final image is formed at the near point. (b) Calculate the length of the compound
microscope also. [25cm, 7, 19.14 cm]
13. The total magnification produced by a compound microscope is 20, while that produced by the eyepiece alone
is 5. when the microscope is focused on a certain object, the distance between objective and eyepiece is 14
cm. Find the focal length of objective and eyepiece, if distance of distinct vision is 20 cm. [5cm, 1.8cm]
14. The magnification produced by the objective of a compound microscope is 8. If the magnifying power of the
microscope be 32, then calculate the magnification produced by the eyepiece. [4] Calculate the refractive
index of the material of an equilateral prism for which the angle of minimum deviation is 60º. [√3]
15. A ray of light passes through an equilateral glass prism, such that the angle of incidence is equal to the angle of
emergence. If the angle of emergence is ¾ times the angle of the prism, calculate the refractive index of the
glass prism. [1.414]
16. A thin prism of refracting angle 2º deviate an incident ray through an angle of 1º. Find the value of refractive
index of the material of the prism. [1.5]
17. Show that the angle of minimum deviation produced by a thin prism is reduced to one-fourth (with respect to
air) when immersed in water. Given that aμg = 3/2 and aμw =4/3.
18. A prism with refracting angle of 60º gives an angle of minimum deviation 53º51’ and 52º for blue, red and
yellow light respectively. What is the dispersive power of the material of the prism? [0.038]
19. One face of a prism of refracting angle 30º and refractive index 1.414 is silvered. At what angle must the ray of
light fall on the unsilvered face so that after refraction into the prism and reflection at the silvered surface it
retraces its path? [45°]
20. A source of red light (λ = 7000 Å) produces interference through two slits placed at a distance of 0.01 cm. At
what distance should a screen be placed from the slits so that interference bands are spaced 0.1m apart?
21. The slits in Young’s experiment have width in ratio 1:16. Deduce ratio of maxima & minima in interference
pattern. [2.78]
22. Yellow light (λ = 6 x 10 -7m) illuminates single slit whose width is 1 x 10 -4 m. What is the distance between
two dark lines on either side of the central maximum if the diffraction pattern is viewed on a screen that is
1.5m from the slit? Ans: 18mm
23. In Young’s experiment, the width of the fringes obtained with light of wavelength 6000 Å is 2.0mm. Calculate
the fringe width if the entire apparatus is immersed in a liquid medium of refractive index 1.33. Ans:1.503 mm
24. Determine the angular separation between central maximum & first order maximum of the diffraction
pattern due to a slit of width 0.25mm when light of wavelength 5890 Å is incident on it normally. Ans: 3.534
x 10 -3 rad
25. A slit of width ‘d’ is illuminated by light of wavelength 6500 Å. For what values of ‘d’ will the (i) First
minimum fall at an angle of diffraction of 30o? (ii) First maximum fall at an angle of diffraction of 30o?