CBSE Important Questions

Light-Reflaction and Refaction

24. Draw the ray diagram in each case to show the position and nature of the image formed when the object is placed:
    1. At the centre of curvature of a concave mirror.
    2. etween the pole P and focus F of a concave mirror.
    3. In front of a convex mirror.
    4. t 2F of a convex lens.
    5. In front of a concave lens.


25. Two lens of focal length +20cm and +50cm are combine .What is the power of two combined lenses?


26. Refractive index of Diamond is 2.42.What is the speed of light in diamond?


27. The magnification produced by a plane mirror is +1, what does this mean?


28. An object 5cm in length is held 25cm away from a converging lens of focal length 10cm. find the position, size and the nature of the image formed.


29. Draw the image by convex lens when object is at
    1. 2f
    2. Between f and 2f
    3. Between f and optical centre


30. Draw the image by concave lens when object is at
    1. Infinity
    2. between f and 2f


31. The power of a lens is +2.5D What kind of lens it is and what is the focal length?


32. Define in spherical mirror the terms, Radius of curvature, Pole, Principle axis,Aperture of mirror, Focus point, and Focal length?


33. An object of size 5cm is placed at a distance of 25cm from the pole of a concave mirror of radius of curvature 30cm. Calculate the distance  and size of the image so formed. What will be the nature of image?


34. An object of 5cm high is placed 15cm in front of a plane mirror, what is the nature, size, position of the image so formed? Why?


35. A virtual, erect, magnified image of an object is to be produced with a concave mirror of focal length 12cm, which of the following distance should be chosen for this purpose?
    1. 10cm
    2. 15cm
    3. 20cm


36. An object 2.5cm high is placed at a distance of 25cm from diverging mirror of focal length 20cm. Find the nature, position and size of the image formed?


37. Draw with concave mirror when object is at
    1. radius of curvature
    2. between C and F


38. Draw with convex mirror when object is at (a) between C and F


39. Write six uses of spherical mirror?


40. Sign Conventions for Reflection by spherical Mirrors.


41. Sign Conventions for Refraction by lens


42. A doctor has prescribed a corrective lens of power + 1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?


43. What is refraction of light? Write a law of refraction.


44. Light enters from air to glass having refraction index 1.50. What is the speed of light in the glass? The speed of light in vacuum is 3×10⁸ m/s


45. An object is placed at a distance of 10cm from a convex mirror of focal length 15 cm. Find the position and nature of the image.


46. An object 5 cm in length is held 25 cm away from a converging lens of focal length 10cm. Draw the ray diagram and find the position, size and nature of the image formed.


47. Write the mirror’s formula. An object of size 7 cm is placed in front of a concave mirror of focal length 18 cm. At what distance from the mirror should a screen be placed, So that a sharp and focused image can be obtained? Find the size and nature of image formed