CBSE Guess > Papers > Important Questions > Class XII > 2007 > Physics > Physics (Optics) By: Mr. Abhishek Gupta

Optics

Q. 1. Define the following terms

1. Reflection
2. Lens
3. Refraction
4. Dispersion

Q. 2. What is total internal reflection. State the 2 condition necessary for it. Hence derive the expression for critical angle in terms of speed of light in the two media

Q. 3. Briefly explain ( with figure )

1. Mirage formation
2. Working of an optical fiber
3. Brilliance of diamond
4. Totally reflecting glass prisms

Q. 4. Red light having a wavelength of 700nm in air enters into a medium having a refractive index 2. Find the velocity, frequency and wavelength of light in this medium. How will the color of the light change.

Q. 5. Draw a ray diagram to show the formation of the image of a point object placed in a medium of refractive index n₁ on the principal axis of a convex spherical surface of radius of curvature R and refractive index n₂. Using the diagram derive the formula for the image distance. Also mention the approximations and sign convention used.

Q. 6. A converging lens of focal length 50cm is placed coaxially in contact with another lens of unknown focal length. If the combination behaves like a diverging lens of focal length 50cm, find the power and nature of the second lens

Q. 7. A converging and diverging lens of equal focal lengths are placed coaxially in contact. Find the power and focal length of the combination

Q . 8. A convex lens of power 2.5D produces an image 4 times as large as the object. Find the 2 possible values of the object distance.

Q. 9. Show that a convex lens produces an N times magnified image when the object distance from the lens is ( F + F/N ) or ( F - F/N ) where F is the focal length of the lens

Q. 10. (a). Plot a graph to show the variation of the angle of deviation as a function of the angle of incidence for light passing through a prism. Derive the relation for angle of deviation in case of the prism having small apex angle.
(b). Using the above derivation, derive the formula for the refractive index of the prism.

Q. 11. A compound microscope with an objective of focal length 1cm and an eye piece of focal length 2cm has a tube length of 20cm. Calculate the magnifying power of the microscope if the final image is formed at the near point of the eye.

Q. 12. Define refractive index and give its SI unit. What is the range of its values.

Q. 13. Where should an object be placed from a converging lens of focal length 10cm so as to obtain a virtual image of magnification 2

Q. 14. Give Reasons for the following observations

1. Sun is visible even before actual sunrise
2. The sky appears blue
3. The clouds are of white color
4. Sun looks reddish at sunrise and sunset

Q.15. Find the apparent depth of the container as seen from the top. μ_A = 1.5 and its depth is 10cm, μ_B is 2 and its depth is 5cm, μ_c = 1.3 and its depth is 13cm

Q. 16. Briefly explain

1. Cauchy formula
2. Rayleigh law C

Q. 17. Red light is incident on a thin converging lens of focal length F. Briefly explain how the focal length of the lens will change if red light is replaced by blue light.

Q. 18. 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 3/4 times the angle of the prism, calculate the refractive index of the prism.

Q. 19. A concave mirror and a concave lens are held separately in water. What changes, if any, do you expect in their focal lengths.

Q. 20. Draw the ray diagram to show the image formation in an astronomical telescope for

1. Normal adjustment
2. Near point adjustment

Derive the expression for magnification in each case.

Q. 21. A ray of light while passing through an equilateral prism undergoes a minimum deviation of 60^o. Find the refractive index of the prism

Q. 22. A converging lens of focal length 20cm is made of refractive index 1.5 .It is immersed in a liquid of refractive index 2. What will be its new focal length. Briefly explain the result

Q. 23. A double concave lens made of glass ( 1.5 ) has both radii of curvature equal to 40cm. An object 2cm high is placed 10cm from this lens. Find the position, nature and size of image formed

Q. 24. Two lenses of power 15D and -5D are in contact with each other forming a combination lens. Find the power and focal length of the combination

b.>An object of size 3cm is placed at 30cm from this combination. Calculate the size and the position of the image formed

Q. 25. You are given two convex lenses of focal length 4cm and 8cm. Using this show the construction of a compound microscope and with a proper ray diagram derive the expression for magnification produced.

Q. 26. Derive the Lens makers formula and the Lens formula

Q. 27. A concavo convex lens is made of refractive index 1.5 and R₁ = 20cm. and R₂ = 10cm. Find its focal length.

Q. 28. What is dispersion. Explain its cause. A prism has μR = 1.4 μ_v = 1.5 . Find the angle of dispersion and the dispersive power.

Q. 29. Derive the expression for apparent depth of a swimming pool. Why does refraction of light occur?

Q. 30. Find the critical angle for water-glass interface. What happens if the angle of incidence is lesser than the critical angle.