GURU NANAK PUBLIC SCHOOL
LIGHT-REFLECTION & REFRACTION
BY- Ranjeet singh
1. Rohit wants to have an erect image of an object using a converging mirror of focal length 40 cm.
(a) Specify the range of distance where the object can be placed in front of the mirror. Justify.
(b) Draw a ray diagram to show image formation in this case.
(c) State one use of the mirror based on the above kind of image formation.
2. Adyasha is looking at herself in a convex mirror in a science museum. Standing 2m away from the
mirror, her image appears to be around half her actual height. Estimate the focal length of the mirror.
3. A concave mirror has a focal length of 20 cm. At what distance from the mirror should a 4 cm tall
object be placed so that it forms an image at a distance of 30 cm from the mirror? Also calculate the size
of the image formed.
4. If the image formed by a spherical mirror for all positions of the object placed in front of it is always
erect and diminished, what type of mirror is it? Draw a labelled ray diagram to support your answer.
5. State two positions on which a concave mirror produces a magnified image of a given object. List two
differences between the two images.
6. A spherical mirror produces an image at magnification -1 on a screen placed at a distance of 50 cm
from the mirror.
(a) Write the type of mirror.
(b) Find the distance of the image from the object.
(c) What is the focal length of the mirror?
(d) Draw a ray diagram to show the image formation in this case.
7. A 10 cm long pencil is placed 5 cm in front of a concave mirror having a radius of curvature of 40 cm.
(a) Determine the position of the image formed by this mirror.
(b) What is the size of the image?
(c) Draw a ray diagram to show the formation of the image.
8. A security mirror used in a big showroom has a radius of curvature 5 m. If a customer is standing at a
distance of 20 m from the cash counter, find the position, nature, and size of the image formed in the
security mirror.
9. Define power of a lens. Find power of a lens whose focal length is 50 cm.
10. The power of a lens is +5 D. An object is placed at a distance of 40 cm from the optical centre of this
lens. State the magnification of the image formed by the lens & also draw a ray diagram to justify your
answer.
12. A student focuses the image of a candle flame, placed at about 20m from a convex lens of focal
length 10 cm, on a screen. After that he moves the screen gradually towards the lens & each time
focuses the image of the flame on the screen.
(i) In which direction does he move the screen to focus the flame on the screen?
(ii) What happens to the size of the image of the flame on the screen?
(iii) What difference is seen in the intensity (brightness) of the images of the flame on the screen?
(iv) what is seen on the screen when the object is very close to the lens (at about 5cm)?
13. If the image formed by a lens for all positions of an object placed in front of it is always erect and
diminished, what type of lens is it? Draw a ray diagram to justify your answer.
If the numerical value of the power of this lens is +10D, what is its focal length in the Cartesian
System?
14. The absolute refractive indices of glass and water are 4/3 and 3/2 respectively. If the speed of light
in glass is 2x10^8 m/s, calculate the speed of light in (i) Vacuum (ii) water.
15. A 4 cm tall object is placed on the principal axis of a convex lens. The distance of the object from
the optical center of the lens is 12 cm, and a sharp image is formed on a screen placed at a distance of
24 cm from the other side of the lens.
Now, if the object is moved a little away from the lens, in which direction will you have to move the
screen to get a sharp image of the object on it again? How will the magnification of the image be
affected?
16. What is meant by power of a lens? Define its SI unit. You have two lenses A and B of focal lengths
+10 cm and -10 cm respectively. State the nature and power of each lens. Also, state the vartual and
magnification of the image formed by each lens when an object is placed at a distance of 20 cm from
the lens. Draw a ray diagram to justify your answer.
17. One half of convex lens of focal length 10 cm is covered with a block paper. Can such a lens
produce an image of a complete object placed at a distance of 30 cm from the lens ? Draw a ray
diagram to justify your answer . A 4cm tall object is placed perpendicular to the principal axis of a
convex lens of focal length 20 cm . Distance of the object from the lens is 15 cm . find the natural
position and size of the image.
18. An object of height 6cm is placed perpendicular to the principal axis of a concave lens of focal
length 5 cm . Use lens formula to determine the position, size & nature of the image if the distance of
the object from the lens is 10cm.
