Class 10 Science
Previous Years Appeared Questions
Chapter 10 Light - Reflection and Refraction
MULTIPLE CHOICE QUESTIONS
1. The correct statement among the following related to the concave lens is (June - 2022)
(A) converges the light rays
(B) diverges the light rays
(C) forms inverted image
(D) forms real image.
Ans. : (B) diverges the light rays
2. To get diminished and real image of an object from a convex lens, the object should be placed (April - 2022)
(A) at principal focus F1
(B) between principal focus F1 and 2F1
(C) beyond 2F1
(D) between principal focus F1 and optical centre O.
Ans. : (C) beyond 2F1
3. An object is kept at the centre of curvature of a concave mirror. The position and nature of the image formed is (June - 2020)
(A) between F and C and inverted
(B) behind the mirror and erect
(C) between F and P and erect
(D) at the centre of curvature and inverted.
Ans. : (D) at the centre of curvature and inverted.
3.
4. To obtain a diminished image of an object from a concave mirror, position of the object should be (F = principal focus, C = centre of curvature, P = pole) (April 2019)
(A) between C and F
(B) beyond C
(C) between P and F
(D) at F
Ans. : (B) beyond C
5. Identify the emergent ray in the given figure. (June 2019)
A) CD (B) BC (C) AB (D) IJAns. : (A) CD
ONE MARKS QUESTIONS
1. Calculate the power of convex lens with a focal length of + 0·5 m. (June - 2022)
Ans. :
Focal length ( f ) = + 0·5 m
Power of lens = 1/focal length
P = 1/f
P = 1/0.5
P = + 2 D
2. Mention the SI unit of power of lens.(April - 2022)
Ans. : dioptre
3. Observe the given incomplete diagram.(Sep - 2020)
4. Convex mirror is commonly used as rear-view mirror in vehicles. Why? (April 2019)
Ans. :
★ Convex mirror always give erect and diminished images
★ As they are curved outwards they have wider field of view.
5. What is the centre of curvature of a spherical mirror ? (June 2019)
Ans. : The reflecting surface of a spherical mirror forms a part of a sphere. This sphere has a centre. This point is called the centre of curvature of the spherical mirror.
TWO MARKS QUESTIONS
1. An object is placed at 25 cm in front of a concave mirror of focal length 15 cm. At what distance from the mirror should a screen be placed in order to obtain a sharp image? (April - 2022)
Ans:
The screen should be placed at a distance of 37·5cm, in front of the concave mirror. 2. A concave lens has focal length of 15 cm. At what distance should the object from the lens be placed so that it forms an image at 10 cm from the lens? (April - 2022)
Ans. :
The object is placed at a distance of 30 cm from the concave lens.
3. Object distance and image distance of a lens are –30 cm and –10 cm respectively. Find the magnification and decide the type of lens used and nature of the image. (Sep - 2020)
Ans. :
★ Here, object distance u = – 30 cm image distance v = – 10 cm
★ Here, as v is negative, the used lens is concave lens.
★ As the magnification is positive and less than one [ having positive sign ] the image formed is erect, virtual and diminished.
4. The focal length of a concave lens is 30 cm. At what distance should the object be placed from the lens so that it forms an image at 20 cm from the lens? (April 2019)
Ans. : Focal length of a lens f = -30cm
Image distance u = -20cm
5. Draw the ray diagram to show the formation of image by a convex lens when the object is at 2F1.
[ F1 : Principal focus ] (April 2019)Ans:
THREE MARKS QUESTIONS
1. a) State the two laws of refraction of light.
b) “The refractive index of diamond is 2·42.” Write the meaning of this statement. (June - 2022)
Ans. : a) Laws of refraction
i) The incident ray, the refracted ray and the normal to the interface of two transparent media at the point of incidence all lie in the same plane.
ii) The ratio of sine of angle of incidence to the sine of angle of refraction is a constant for the light of a given colour and for the given pair of media /
(OR) sini/sinr = Constant.
The ratio of the speed of light in air and the speed of light in diamond is 2·42.
2. Draw the ray diagram of image formation when the object is kept at 2F1 of the convex lens. With the help of the ray diagram, mention the position and nature of the image formed. [F1 : Principal focus of the lens ] (June - 2022)
Ans:
Position of the image : At 2F2Nature of the image : Real and inverted
3. Draw the ray diagram of image formation when the object is kept between C and F of the concave mirror. With the help of the ray diagram mention the position and the nature of the image formed. [ F : Principal focus of the mirror, C : Centre of curvature of mirror ] (June - 2022)
Ans:
Position of the image : Beyond CNature of the image : read and inverted.
4. Draw the ray diagram to show the image formation by a convex lens, when the object is kept at 2F1 of the lens. With the help of the ray diagram mention the position and nature of the image formed. [ F1 : Principal focus of the lens ] ( April - 2022)
Ans:
Position of the image — At 2F2 Nature of the image — Real and inverted
5. a) State the laws of refraction of light.
b) In the given figure, AB is the incident ray, BC is the refracted ray and MN is the normal at the point of incidence. Which medium is more denser ? Why ? (Sep - 2020)
Ans:
a)
★ Laws of refraction of light : The incident ray, the refracted ray and the normal to the interface of two transparent media at the point of incidence, all lie in the same plane.
★ The ratio of sine of angle of incidence to the sine of angle of refraction is a constant for the light of a given colour and for the given pair of media.
OR
★ If i is the angle of incidence and r is the angle of refraction, then, sini/sinr = constant.
b)
★ Medium 1 is more denser.
★ When a ray of light travels from rarer medium to denser medium, it always bends towards the normal.
6. a) Differentiate between convex mirror and concave mirror.
b) Define the principal focus of a convex lens. (Sep - 2020)
Ans:
b) The rays of light falling on a convex lens parallel to the principal axis, after refraction from the lens converge to a point on the principal axis. This point on principal axis is called the ‘principal focus’ of the convex lens.
7. An object is kept on the principal axis of a concave mirror of focal length 12 cm. If the object is at a distance of 18 cm from the mirror, calculate the image distance. Determine the nature of the image formed by calculating the magnification produced by the mirror. (June - 2020)
Ans. :
Focal length of concave mirror f = -12 cm
Object distance u = – 18 cm
8. A doctor prescribes a corrective lens of power – 0·5 D to a person. Find the focal length of the lens. Is this lens diverging or converging ? Give reason. How does the property of this lens can be used to correct eye defects ? (June - 2020)
Ans. :
★ Because power of a lens is negative means the given lens is concave.
★ The diverging property of the lens is used to correct myopia. In myopic eye the image of a distant object is formed in front of the retina and not on the retina.
★ A concave lens of suitable power diverges the light rays and brings the image back on the retina.
9. Draw the ray diagram when the object is kept between 1F and 12F of the convex lens. With the help of the diagram mention the position and nature of the image formed. [ 1F : Principal focus of the lens ] (June - 2020)
Ans:
Position of the image-beyond 2F2Nature-real inverted and enlarged.
10. Draw the ray diagrams for the image formation in a convex lens when an object is placed
(i) at focus F1 (ii) beyond 2F1. (April 2019)
Ans:
(i) at focus F1
11. A concave lens has focal length 30 cm. At what distance should the object be placed from the lens so that it forms an image at 20 cm from the lens ? Also, find the magnification produced by the lens. (June 2019) Ans:
FOUR MARKS QUESTIONS
Marks Questions
1. Answer the following questions :
a) Write any four uses of concave mirror.
b) An object is placed at a distance of 15 cm on the principal axis in front of a concave lens with a focal length of 10 cm. Find the image distance. (June - 2022)
Ans. :
a) Uses of concave mirror.
i) Used in torches, search-lights
ii) Used in vehicles head lights
iii) Used as shaving mirrors
iv) The dentists used to test / examine teeth of patients
v) Used in solar furnace. (Any four)
b) Given
f = – 10 cm,
u = – 15 cm
FIVE MARKS QUESTIONS
1. a) What is refraction of light ? State two laws of refraction of light.
b) What is refractive index of light ? “The refractive index of diamond is 2·42.” What is the meaning of this statement ? (April - 2022)
Ans:
a)
★ Light travelling obliquely from one medium to another, the direction of propagation of light in the second medium changes
★ The incident ray, the refracted ray and the normal to the interface of two transparent media at the point of incidence all lie in the same plane
★ The ratio of sine of angle of incidence to the sine of angle of refraction is constant, for the light of given colour and for the given pair of media / sini/sinr = constant
b) The ratio of speed of light in air and the speed of light in medium. The ratio of speed of light in air and the speed of light in diamond is 2·42.
IMPORTANT QUESTIONS
1. Four objects A , B , C and D have refractive index 1.50 , 1.36 , 1.77 and 1.31 respectively. Which object will shine more ?
a) Object A b) Object B
c) Object C d) Object D
Ans : c) Obect C
Explanation : As the refractive index of an object increases it shines more
2. An object is placed between f and 2f of a convex lens. Correct statement for the image formed here is
a] real and larger than object
b] inverted and equal size
c] erect and smaller than object
d] virtual and larger than object
Ans : a] real and larger than object
3. Four convex lens P , Q , R and S have focal length 20cm , 15cm, 5cm and 10cm respectively. The power of lens is more in -
a] P b] Q c] R d] S
Ans : c] R
Explanation : Power of lens is inversely proportional to focal length
4. An object was kept at any distance from concave lens , the nature of the image is
a] virtual , erect and larger than object
b] virtual , inverted and smaller than object
c] virtual , erect and smaller than object
d] virtual , erect and equal size
Ans : c] virtual , erect and smaller than object
5. Mention the conditions when a ray of light travels from one media to another, refraction does not take place.
Ans :
★ If the angle of incidence is equal to 90^0 or 0^0
★ If the refractive indexes of both media are same.
6. A ray of light travelling in air enters obliquely into water. Does the light ray bend towards the normal or away from the normal? Why?
Ans :
★ The light-ray bends towards the normal
★ Because the ray of light goes from a rarer medium to a denser medium.
7. The refractive index of diamond is 2.42. What is the meaning of this statement?
Ans : The refractive index of diamond is 2.42, It mean that the speed of light in diamond is lower by a factor of 2.42 relative to that in vacuum.
8. Light enters from air to glass having refractive index 1.50. What is the speed of light in the glass ? The speed of light in vacuum is 3 x 10^8 ms-1.
9. Observe the information given in Table
In which of these does the light travel fastest? Give reason to your answer.
Ans :
★ In water light travels faster.
★ Because water has the lowest refractive index, therefore light travels fastest in this optically rarer medium than kerosene and turpentine oil.
10. Observe the information given in Table
Find out the medium having highest optical density. Give reason to your answer
Ans : Diamond has highest optical density
★ As the refractive index of a media increases , its optical density also increases.
11. The magnification produced by a lens is +1. What does this mean?
Ans :
(i) m = 1 indicates the size of image is same as that of object.
(ii) positive sign of m indicates that an erect image is formed.
12. Define power of lens. What is its SI unit?
Ans: Power of lens is defined as the reciprocal of its focal length. If P is the power of a lens of focal length f in metres,
then P = 1/ f
The S.I. unit of power of a lens is Dioptre. It is denoted by D.
13. Find the focal length of a lens of power -2.0 D. What type of lens is this ?
Ans: Here, P = -2.0 D
Focal of length of lens f = 1/P
f = 1/−2 = −0.5m
The type of lens is concave because the focal length is negative.
14. Draw the ray diagrams for the image formed by the concave mirror when an object was kept at
i) Beyond C ii) At C iii) Between C and F
Ans:
15. A 10 cm long awl pin is placed vertically in front of a concave mirror. A 5 cm long image of the awl pin is formed at 30 cm in front of the mirror. Find the focal length of this mirror .
Ans:
16. Rays from Sun converge at a point 15 cm in front of a concave mirror. Where should an object be placed so that size of its image is equal to the size of the object?
(a) 15 cm in front of the mirror
(b) 30 cm in front of the mirror
(c) between 15 cm and 30 cm in front of the mirror
(d) more than 30 cm in front of the mirror
Ans : (b) 30 cm in front of the mirror
17. Observe the information given in Table
In which of these does the refracted ray bends more towards normal ? Give reason to your answer. Ans : In Gycerine , because it is more optically denser than others. When light travels from rare medium to denser medium the refracted ray bends towards normal.
18. Refractive index of diamond with respect to glass is 1.6 and absolute refractive index of glass is 1.5. Find out the absolute refractive index of diamond.
Ans:
Given : Refractive index of diamond with respect to glass = 1.6
Refractive index of glass =1.5
Then , Absolute refractive index of diamond = 1.6 x 1.5 = 2.4
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