# LIGHT: REFLECTION AND REFRACTION– 5 Mark Questions

Q1.         (i)  Define the following terms in context of spherical mirrors.

(a)  Pole

(b) Centre of curvature

(c) Principal axis

(d) Principal focus

(ii)   Draw ray diagrams to show the principal focus of a

(a)  concave mirror and

(b) convex mirror

(iii)   Consider the following diagram in which M is a mirror and P is an object and Q is its magnified image formed by the mirror. State the type of the mirror M and one characteristic property of the image Q.

Q2.   It is desired to obtain an erect image of an object, using concave mirror of focal length of 12 cm.

(i)  What should be the range of distance of an object placed in front of the mirror?

(ii)  Will the image be smaller or larger than the object?  Draw ray diagram to show the formation of image in this case.

(iii) Where will the image of this object be, if it is placed   24 cm in front of the mirror? Draw ray diagram for this situation also to justify your answer.

Show the positions of pole, principal focus and the centre of curvature in the above ray diagrams.

Q3.  A student wants to project the image of a candle flame on the walls of school laboratory by using a lens.

(i) Which type of lens should he use and why?

(ii)  At what distance in terms of focal length F of the lens should he place the candle flame, so as to get

(a)  a magnified and

(b) a diminished image respectively, on the wall?

(iii) Draw ray diagrams to show the formation of the image in each case.

Q4.   One half of a convex lens of focal length 10 cm is covered with a black 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.

Q5. A 4 cm tall object is placed perpendicular to principal axis of a   convex lens of focal length 20 cm.  The distance of the object from the lens is 15 cm.   Find the nature, position and the size of the image.

Q6.  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. Which of the two lenses will form a virtual and magnified image of an object placed 8 cm from the lens?   Draw a ray diagram to justify your answer.

Q7. Suppose you have three concave mirrors A, B and C of focal lengths 10 cm, 15 cm and 20 cm. For each concave mirror, you perform the experiment of image formation for three values of object distances of 10 cm, 20 cm and 30 cm. By giving reason, answer the following:

(i) For the three object distances, identify the mirror/mirrors which will form an image of magnification -1.

(ii) Out of the three minors identify the minor which would be preferred to be used for shaving purposes/ makeup.

(iii) For the mirror   B draw ray diagram for image formation for object distances 10 cm and 20 cm.

Q8. A student wants to project the image of a candle flame on the walls of the school laboratory by using a mirror.

(i) Which type of mirror should he use and why?

(ii) At what distance, in terms of focal length ‘f’ of the mirror, should he place the candle flame to get the magnified image on the wall?

(iii) Draw a ray diagram to show the formation of the image in this case.

(iv) Can he use this mirror to project a diminished image of the candle flame on the same wall? State ‘how’ if your answer is ‘yes’ and ‘why not’ if your answer is ‘no.’

Q9. Draw a ray diagram in each of the following cases to show the position and nature of image formed when the object is placed:

(i) Between pole and focus of a concave mirror.

(ii) Between focus and centre of curvature of a concave mirror.

(iii) At the centre of curvature of a concave mirror.

(iv) Between infinity and pole of a convex mirror.

(v) At infinity from a convex mirror.

Q10. (i) Define focal length of a spherical lens.

(ii) A divergent lens has a focal length of 30 cm. At what distance should an object of height 5 cm from the optical centre of the lens be placed so that its image is formed 15 cm away from the lens ? Find the size of the image also.

(iii) Draw a ray diagram to show the formation of image in the above situation.

Q11. (i) Define power of a lens. Write its SI units.

(ii) You are provided with two convex lenses of focal length 15 cm and 25 cm, respectively. Which   of the two is of larger power? Give reason for your answer.

(iii) A 20 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 10 cm. The distance of the object from the lens is 15 cm. Find Ute nature, position and size of the image. Also find its magnification.

Q12. (i) Draw a ray diagram to show the formation of image by a convex lens when an object is placed in front of the lens between its optical centre and principal focus.

(ii) In the above ray diagram mark the object-distance (u) and the image-distance (v) with their proper signs (+ve  or – ve as per the new  Cartesian sign convention)  and state how these distances are related to the focal length  (f) of the convex lens in this case.

(iii) Find the power of a convex lens which forms a real, and inverted image of magnification -1of an object placed at a distance of 20 cm from its optical centre.

Q13. (i) Two convex lenses A and B have powers P1 and P2 respectively and P2   is greater than P1 Draw a ray diagram for each lens to show which one will be more converging.  Give reason for your answer.

(ii) A 2.0 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 10 cm. The distance of the object from the lens is 15 cm. Find the nature, position and size of the image. Also find its magnification.

Q14.  (i) Define the following term related to spherical mirror.

(b) Pole

(c) Principal focus

(ii) Mention the differences between real image and virtual image.

Q15.  (i) Draw ray diagrams and show the nature of images formed in the following cases, when

(a) object is placed between F and 2F in front of concave lens,

(b) object is placed between F and 2F in front of convex lens.

(ii) An object 50 cm is placed on the principal axis of a convex lens. Its 20 cm tall image is formed on the screen placed at a distance of 10 cm from the lens. Calculate the focal length of the lens.

Q16.       The image of an object placed at 60 cm in front of a lens is obtained on a screen at a distance of 120 cm from it.  Find the focal length of the lens.  What would be the height of the image, if the object is 5 cm high?

Q17.  ( i) Two lenses  have power of

(a)+ 2D

(b) – 4D.

What is the nature and focal length of each lens?

(ii) An object is kept at a distance of 100 cm from each of the above lenses. Calculate the

(a) image distance and

(b) magnification in each of two cases.

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