CBSE Class 10 Science Chapter-10 Light Reflection and Refraction – Free PDF Download
Free PDF download of Important Questions with Answers for CBSE Class 10 Science Chapter 10 – Light Reflection and Refraction prepared by expert Science teachers from latest edition of CBSE(NCERT) books only by CoolGyan to score more marks in CBSE board examination.
CBSE Class 10 Science Chapter-10 Light Reflection and Refraction Important Questions
CBSE Class 10 science Important Questions Chapter 10 – Light Reflection and Refraction
2 Mark Questions
1. A beam of rays, parallel to the principal axis, is incident on a convex mirror. Show diagrammatically, the path of these rays after reflection from the mirror.
Ans.
2. Find the power of a concave lens of focal length 2 m?
Ans. 
3. With respect to air the refractive index of ice is 1.31 and that of rock salt is 1.54. Calculate the refractive index of rock salt with respect to ice?
Ans. 
4. A concave mirror produces three times magnified (enlarged) real image of an object 10 cm in front of it. Where is the image located?
Ans. 
5. Three mirrors, one plane, one concave and one convex are lying on the table. How can a person identify them without touching them or using any other apparatus or device?
Ans. Plane mirror produces the image of same size. Concave mirror produced the magnified image while the convex mirror will produce a diminished image.
6. Obtain the formula for the focal length of a lens in terms of object distance (u) and magnification (m)
Ans. 
7. In what S.I unit is the power of lens stated? A convex lens has a focal length of 50 cm. calculate its power?
Ans. S.I unit of power is Dioptre (D)
F=50 cm
8. Light enters from air into diamond which has a refractive index of 2.42. Calculate the speed of light in diamond. The speed of light in air is 
m/s.
Ans. 
=?
9. Light is incident at an angle of
(i)
(ii)
, on the same face of a given rectangular slab. If the angles of refraction, at this face are 
in the two cases. Obtain the relation between these two angles.
Ans. 
10. Why do we prefer a convex mirror as a rear view mirror in vehicles?
Ans. Convex mirror is preferred as rearview mirror is vehicles because it always forms virtual erect and diminished image. If also covers the wider field of view.
11. A doctor has prescribed a corrective lens of power 1.5 D. Find the focal length of this lens. Is the prescribed lens diverging or converging.
Ans. 
Positive sign means it is a converging lens.
12. Define the principle focus of a concave mirror.
Ans. Principal focus of a concave mirror is the point on its principal axis, where light rays coming parallel to principal axis actually converge after reflection from mirror.
13. The radius of curvature of a spherical mirror is 20 cm. what is its focal length?
Ans. Focal length (f)= R/2 = 20 cm/2 = 10 cm.
14. Name a mirror that can give an erect and enlarged image of an object.
Ans. Only a concave mirror can give a erect and enlarged image of an object.
15. Why do we prefer a convex mirror as a rear-view mirror in vehicles?
Ans. We prefer a convex mirror as a rear-view mirror in vehicles because a convex mirror gives an erect and diminished image. As a result, convex mirror help the driver to have much wider field view.
16. Find the focal length of a convex mirror whose radius of curvature is 32 cm.
Ans. Radius of curvature of (R) = 32 cm
Focal lengh(f) = R/2 = 32/2 cm = 16 cm.
17. A concave mirror produces three times magnified real image of an object placed at 10 cm in front of it. Where is the image located?
Ans. Distance of object from concave mirror (u)= -10 cm.
Magnification (m) = -3
m = -v/u
v = -mu = -(3) x (-10) = -30 cm.
18. A ray of light traveling in air enters obliquely into water. Does the light ray bend towards or away from the normal? Why?
Ans. The light bends towards the normal on entry into water. It is due to the fact that as compared to air, the water is optically denser medium.
19. Find out, from Table (10.3), the medium having highest optical density. Also, find the medium with lowest optical density.
Ans. As per table, diamond has highest optical density (2.42). Medium with lowest optical density is air (1.0003)
20. You are given kerosene, turpentine and water. In which of these does the light travel fastest? Use the information given in table 10.3
Ans. As the refractive index of water is least out of three substances. Hence speed of light is maximum in water. So, light travels fastest in water.
21. The refractive index of diamond is 2.42. What is the meaning of this statement?
Ans. It means that speed of light in diamond is 2.42 times slower than speed of light in air.
22. Absolute refractive Index of some of material is tabulated below
i) In which of these does light travel fastest and why?
ii) arrange these materials in ascending order of their optical densities.
Ans. i) Water due to least refractive index.
ii) Water, Kerosene, Rock salt, diamond
23. A rod of length 10 cm lies along the principal axis of a concave mirror of 10 cm in such a way that the end closer to the pole is 20 cm away from it. Find the length of image?
Ans. R =2f=2O cm. Thus the nearer end B of the rod AB is at C and hence its image will be formed at B itself
For end A u = -30 cm, f= -10 cm, v = -15 cm Length of image will be at 5 cm
24. Two lenses 1&2 are placed in contact. Focal length of lens 1 is 20 cm and of 2 is – 10 cm. Calculate
i) Total Power of combination
ii) What is the nature of combination.
Ans. (i) P= -5 D
(ii) Concave Lens
25. An object is placed 15 cm in front of a lens ‘A’ and lens gives real, inverted, magnified image and formed at large distance. Lens ‘A’ is replaced by Lens ‘B’ and a real, inverted image of the same size as of object is formed.
i) What is the nature of Lens A&B?
ii) What is the focal length of A&B?
Ans. A=Convex lens, B=Convex Lens
An Object is placed and lens gives real, inverted
ii) 
26. A fish under water is viewing obliquely a fisherman standing on the bank of lake. Does the man look taller or shorter?
Ans. As light travels from rarer to denser medium, it bends towards normal and appears to come from greater height. Therefore, to fish under water man looks taller.
27. What type of lens must be placed at XV so that image I shifts to I’
Ans. concave lens
28. Identify the type of lens or mirror placed at XV where 0 is object and I is image.
Ans. Convex lens (when object is placed between pole and focus)
29. An object is placed at a distance of 50 cm from a convex minor. State two characteristics of the image formed.
Ans. (1) Image is virtual and erect.
(2) Image is diminished.
30. Write two uses of concave mirror.
Ans. (1) Used as reflectors for automobile headlights.
(2) Used as shaving mirror.
31. An object 1 cm high produces a real image 1.5 cm high, when placed at a distance of 15 cm from concave minor. Calculate the position of the image.
Ans. —v/u=h’/h, -v/-15-l.5
v = 15x 1.5 = -22.5 cm.
32. Find the power of a concave lens of focal length 2m.
Ans. —p= 1/f
=1 = -0.5 D.
33. Which phenomenon occurs when light falls on
(a) highly polished surface
(b) a transparent medium?
Ans. (a) Reflection of light.
(b) Refraction of light.
34. What will happen to a ray of light when it falls normally on a surface?
Ans. No bending of light ray occurs. It means light rays goes straight from one medium to another.
35. What is absolute refractive index?
Ans. When first medium is taken as vaccum, the refractive index of second medium is called as absolute refractive index.
36. If refractive index of glass is 1.65, What is the speed of light in glass?
Ans. Given Refractive index = n = 1.65
speed of light in vaccum = 3*108 m s-1
Using, Refractive Index= speed of light in vaccum/ speed of light in glass
1.65 = 3*108 ms-1 / speed of light in glass
speed of light in glass = 3*108 /1.65
= 1.8*108 m s-1
Therefore, speed of light in glass is 1.8 *108 ms-1
37. The magnification “m” for a mirror is +1 what does this signif.
Ans. (a) Image is of same size as the object.
(b) Image is virtual and erect.
