Q1. The radius of curvature of a spherical mirror is 30 cm. What is its focal length ?
Q2. An object is placed at (a) 10 cm, (b) 5 cm in front of a concave mirror of radius of curvature 15 cm. Find the position, nature, and magnification of the image in each case.
Q3. What do you understand by term ‘reflection of light’ ?
Q4. Define refractive index of a medium.
Q5. Define optical centre of a lens.
Q6. Define the first principle focus of a convex lens.
Q7. Define the focal length of a lens.
Q8. What do you understand by the term ‘power of lens’ ?
Q9. Give two characteristics of the image formed by a concave lens .
Q10. State two application of convex lens .
Q11. What is the unit of refractive index ?
Q12. What is the refractive index of vacuum ?
Q13. Which of the two is a diverging lens : convex or concave ?
Q14. A lens forms an inverted image of an object. What kind of lens is this ?
Q15. Give the name of the point on the principle axis of a lens through which light passes undeviated ?
Q16. Name a lens which forms always virtual and erect .
Q17. Where should an object be placed in order to use a convex lens as a magnifying glass ?
Q18. For what position of a lens related to its focal length ?
Q19. Which physical quantity does the unit dioptre represent ?
Q20. Math the following:
(a) No refraction, if the two medium have (1) concave lens
(b) Thick at the centre and thin at the edges (2) same refractive index
(c) A lens which always produce magnification less than 1 (3) convex lens
(d) Convex lens forms image of same size as size of a object if it is placed (4) positive
(e) Power of convex lens (5) at a distance 2F
Q21. Write ‘True’ or ‘False’
A. When a ray of light passes from one medium to another, its direction does not change but frequency.
B. When a ray of light indent normally on a surface of transparent medium, refracted ray bends toward normal.
C. A lens which is thin at the centre and thick at the edges is called concave lens .
D. A concave lens can form real image if the object be placed at the focus .
E. A ray of light passing through the focus of a convex lens, after refraction from the lens it becomes parallel to the principle axis .
F. A convex lens cannot form virtual image .
G. A ray of light passing through the optical centre goes undeviated.
Q22(a). If the refracted ray bends toward the normal the second medium is said to be …………………….. .
(b). The twinkling of stars is due to ……………………………..
(c) A convex lens ………………………… rays of light.
(d) A concave lens …………………… rays of light .
(e) The image formed by a concave lens is always ………………………..and ………………………. .
(f) If the object be placed at a distance 2F in front of a convex lens then magnification produced is …………………… .
(g) The power of a lens is -2 D, it is a lens.
(h) The power of a lens is +4 D, its focal length is ……………………………… cm.
Q23. Numerical problem :
1. With respect to the air the refractive indices of water and benzene are 1.33 and 1.50 respectively. Calculate the refractive index of benzene with respect to water.
2. Light enters from air into glass plate which has a refractive index of 1.5. Calculate the speed of light in glass. (Give, speed of light in vacuum is 3x108 ms -1) .
3. An object is placed at a distance of 20 cm from a convex lens of focal length 30 cm. Find the position and nature of image formed.
4. Calculate the distance at which an object should be placed in front of convex lens of focal length 24 cm to obtain a virtual image double its size ?
5. An object is placed at the focus of a concave lens of a focal length 30 cm. Find the position of nature of image formed .
6. Find the power of a concave lens of focal length 2 m .
7. Light enters from air to diamond with refractive index 2.42. What is the speed of light in diamond? Given speed of light in air is 3 x 108 m/s.
Q24. Draw a ray diagram to illustrate the action of a converging lens as a magnifying glass .
Q25. Choose the correct answer in the following questions :
1. A ray of light travelling into air enters into glass obliquely :
a. is refracted towards the normal
b. is refracted away from the normal
c. is not refracted
d. goes along the boundary
2. A ray of light is incident normally on the surface of water. Its angle of refraction in water is :
a. 90
b. 0
c. 180
d.45
3. With respect to the air the refractive indices of water and glass are 4/3 and 3/2 respectively. The refractive index of glass with respect to water is :
a. 2 b. 8/9 c. 9/8 d. 1
4. When a ray of light passes from one medium to another, which of the following does not change ?
a. Wavelength b. Speed c. Intensity d. Frequency
5. The point of the principal axis of a lens through which a ray of light passes without any deviation is called :
a. focus b. optical centre c. centre of curvature d. pole
6. The magnification produced by a concave lens is :
a. equal to 1 b. greater than 1 c. less than 1 d. may be 1
7. A student obtained a sharp image of the grill of a window on a screen, using a convex lens. For getting better results , the teacher suggested focussing of a distance tree instead of a grill. In which direction should the lens be moved for this purpose ?
a. Away from the screen b. Very far away from the screen c. Behind the screen d. Towards the screen
8. An object is placed at a distance 8 cm in front of a convex lens of focal length 20 cm. The image formed is :
a. real and enlarged b. real and inverted c. virtual and enlarged d. virtual and diminished
Q26. Comparison between real and virtual images.
Q27. Define 1 dioptre of power of lens .
Q28. The image formed by a concave mirror is observed to be virtual, erect and larger than than the object. Where should be the position of the object ?
A. Between principle focus and centre of curvature
B. At centre of curvature
C. Beyond centre of curvature
D. Between pole of the mirror and its principle focus
Q29. No matter how far you stand from a mirror, your image appears erect. The mirror is likely to be
A. Plane b. concave c. convex d. either plane or convex
Q30. Which of the following lenses would you prefer to use while reading small letters found in a dictionary ?
A. A convex lens of focal length 50 cm.
B. A concave lens of focal length 50 cm.
C. A convex lens of focal length 5 cm.
D. A concave lens of focal length 5 cm
Q31. We wish to obtained an erect image of an object, using a concave mirror of focal length 15 cm. What should
be the range of distance of the object from the mirror ? What is the nature of image ? Is the image larger or
Smaller than the object ? Draw a ray diagram to show the image formation in this case .
Q32. One half of a convex lens is covered with a black paper. Will this lens produce a complete image of the object ?
Verify your answer experimentally. Explain your observation .
Q33. A doctor has prescribed a corrective lens of power + 1.5 D. Find the focal length of the lens. Is the prescribed
lens diverting or converging ?
Q34. Define principal focus of concave mirror.
Q35. If we place convex lens towards the Sun, the light from the sun is focussed
A. Far away from the sheet
B. On a sheet of paper
C. Between F and C
D. None of the above
Q36. The spot on the paper represents
A. Image of the lens
B. Image of the sun
C. Image of the paper
D. None of these
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