### REFRACTION OF LIGHT AT CURVED SURFACES

1. How many types of images forms due to lenses? What are those? Mention the differences between them. (AS1) 4 Marks
A:
There are two types of images formed due to the lenses. They are the real and virtual images.

2. Compare and contrast the Convex lens and Concave lens. (AS 1) 4 Marks
A:

3. How do you verify experimentally that the focal length of a convex lens is increased when it is kept in water.
(OR)
Explain how the focal length of the lens depends upon the surrounding medium.                                                                                                 (AS 3) 4 Marks
A: AIM:
To verify change in focal length of a lens when it is dipped in water.
Apparatus: Convex lens of known focal length, circular lens holder, tall cylindrical glass tumbler, black stone, water.
Procedure:
* Take a convex lens whose focal length is known.
* Take a glass jar whose height is twice that of focal length of lens.
* Take a black coloured stone and place it in a jar.

* take a circular holding lens and view the stone keeping if at a distance less than focal length. And go on increasing the distance between the stone and lens, you can view the stone till the distance between stone and lens is equal to focal length.
* After the focal length distance you can't view the stone.
* Now pour water in the glass tumbler and view the stone. By placing the lens at a distance which we did not view the stone.
* Now you can view the stone clearly. From this experiment we can conclude that the focal length goes on increasing with respective to media.

4. List out the apparatus required to find the focal length of a Convex lens and describe the procedure to find the focal length? (AS 3) 4 Marks
A: AIM:
To determine the focal length of a Convex lens.
Apparatus: Convex lens, meter scales, V-stand, screen, candle.
Procedure:
* Take a V-stand and place it on a long (nearly 2 m) table at the middle.
* Place a Convex lens on the V-stand.
* Light a candle and take it far away from the lens along the principal axis.
* Adjust the screen on the other side of the lens to get a clear image on it.
* Measure the distance between the V-stand and the screen. This value represents the image distance (v).
* Now place the candle at the distance of 60 cm from the lens, such that the flame of the candle lies along the principal axis of the lens.
* Adjust the screen to get a clear image and measure the values of object distance (u) and image distance (v) and note them in a table.
* Repeat the above step for various distances like 50 cm, 40 cm, 30 cm etc. Measure the image distance corresponding to each position of the object and note the values in the table.

* Calculate the focal length for each case, we find that the focal length remains constant for a given lens.

5. A Student conducted experiment with biconvex lens and prepared the following table.

Answer the following questions based on the information given in the above table.
i) What is the reason you think for different values of focal length in the above table?
ii) How do you decide the focal length of the above lens?
iii) Can you measure the image distance making the object distance as 10 cm? Why?
iv) What relation have you identified among u, v and f? (AS 4) 4 Marks
A: i) Reasons for different values of focal length in the above table.
a) Accuracy is not followed while measuring object distance and image distance.
b) While catching the image on the screen, the person could not get sharp image and measured that distances for image distances.
ii) The focal length can be measured by taking the average of the experimental values.

iii) No, because the object is placed between optical centre and focal point. So, we will get a virtual enlarged image which can be seen in the lens.
iv) From the table, the relation among u, v and f

6. Describe the image formation by a Convex lens for various positions of the object. (AS 1) 4 Marks
A:
i) Object at infinity: The rays coming from the object at infinity are parallel to principal axis and converge to the focal point after refraction. So, a point sized image is formed at the focal point

ii) Object placed beyond the centre of curvature on the principal axis: When an object is placed beyond the centre of curvature, a real, inverted and diminished image is formed on the principal axis between F1 and C1.

iii) Object placed at the centre of curvature: When an object is placed at the centre of curvature (C2) on the principal axis, a real inverted image is formed at C1, which is same size as that of the object.

iv) object placed between the centre of curvature and focal point: When an object is placed between centre of curvature (C2) and focus (F2) we will get an image which is real, inverted and magnified. This image will form beyond C1

v) Object located at focal point: When an object is placed at focus (F2), the image will be at infinity.

vi) Object place between focal point and optic centre: If we place an object between focus and optic centre, we will get an image which in virtual, erect and magnified."

7. Fill the table with the given ray diagrams information.

A:

8.

With the help of above figure answer the questions.
i) Name the lens used in the above figure.
ii) Explain the nature of image.
iii) Out of the two light ray travelling from the object, which one is deviated and which is not?
iv) To get the image at infinite distance, where should we place the object. Convey this by means of a ray diagram.  (AS4) 4 Marks

A: i) Convex lens.
ii) Real, inverted and of the same size as that of object.
iii) R1 is deviated but R2 not deviated.
iv)

9. Observe the diagram and answer the following.

i) State the position of object.
ii) Compare distances of object and image from lens.
iii) Write characteristics of image.
iv) Where we placed an object to get enlarged virtual image formed by this lens?
(AS4) 4 Marks
A:
i) Between 2F2 and F2.
ii) Image distance is more than object distance.
iii) Inverted, magnified and Real image.
iv) Between F2 and P.

10. Complete the following table by writing the characteristics of object when placed in different positions on the principle axis by using a Convex lens.     (AS4) 4 Marks

 Position of  the object Position of  the image Nature of the image the Size of the image At infinity Beyond 2F2 At 2F2 Between 2F2 and F2 At F2 Between F2 and P

11. A Convex lens is made up of two different materials as shown in the following figure. How many of images does it form? Explain. (AS1) 2 Marks

A: If forms two images.
Reason: A Convex lens made up of two different materials of refractive indices n1, n2 has two focal lengths. Thus it forms two images for a given object.

12. Draw any two ray diagrams shows real images of Convex lens.
(AS5) 2 Marks

A:

13. Draw a ray diagram shows a point sized image with Convex lens. (AS5) 2Marks
A:

14. Draw a ray diagram shows an virtual image of a Convex lens. (AS5) 2 Marks
A:

15.

Complete the ray diagram to show the path of the ray after refraction through the lens shown in the figure. (AS5) 2 Marks
A:

16. Complete the ray diagram to show the path of the ray after refraction through the lense shown in the figure. (AS 5) 2 Marks

A:

17. A line is drawn from the centre of curvature to the point on the curved surface. How is the line related to the curved surface? (AS 1) 1 Mark
A:
It is a normal.

18. What happens to the ray that is incident on a curved surface when it travels from rarer medium to denser medium? (AS1) 1 Mark
A:
It bends towards the normal.

19. What happens to the ray that is incident on a curved surface when it travels from denser medium to rarer medium? (AS 1) 1 Mark
A:
It bends away from normal.

20.

What happens to the ray that travels along the principal axis? (AS 5) 1 Mark
A:
It does not deviate.
21.

What happens to the ray that travels through the centre of curvature?
(AS 5) 1 Mark

A: It does not deviate

22. Which law says that the ray which travels along the normal drawn to the surface does not deviate from its path? (AS 1) 1 Mark
A:
Snell's law.

23. What is minimum number of curved surface of a lens? (AS 1) 1 Mark
A:
One.

A: Biconvex lens

A:
Biconcave

A:
Plano - convex

A:
Plano - concave.

A:
Concave - convex.

29. Which lens is thick at the middle and thinner at edges? (AS 1) 1 Mark
A:
Biconvex lens.

30. Name the lens whose surfaces are curved inwards? (AS 1) 1 Mark
A:
Biconcave lens.

31. Which lens is thin at the middle and thicker at the edges? (AS 1) 1 Mark
A:
Biconcave lens.

32. What do we call the line joining C1 and C2? (AS1) 1 Mark
A:
Principal axis.

33. What do we call the midpoint of the lens? (AS1) 1 Mark
A:
Optic centre of the lens.

34. What is the symbol used to represent a Biconvex lens? (AS5) 1 Mark
A:

35. Draw the symbol used to represent biconcave. (AS5) 1 Mark
A:

36. How does the ray which travels along the principal axis of a lens behave?                                                                                                             (AS5) 1 Mark
A:
Any ray which travels along principal axis does not deviate from its path.

37. Draw the diagrams related to the behaviour of light rays travelling along the principal axis. (AS5) 2 Marks
A:

38. How does the ray passing through the optic centre of a lens behave?
(AS1) 1 Mark
A:
It does not deviate.

39. Draw the figures related to the behaviour of a ray passing through the optic centre of lens? (AS5) 2 Marks
A:

40. How do the rays travelling parallel to the principal axis behave?
(AS1) 1 Mark
A:
The rays either converge at focus or diverge.

41. Draw the figures illustrating the behaviour of rays passing parallel to the principal axis of a convex lens. (AS 5) 2 Marks
A:

42. Draw the figures illustrating the behaviour of rays passing parallel to the principal axis of a Concave lens. (AS5) 2 Marks
A:

43. Draw a figure to show that a ray passing through the principal focus after refraction travels parallel to the principal axis. (AS5) 2 Marks
A:

44. What happens when parallel rays of light fall on a lens making certain angle with principal axis? (AS1) 2 Marks
A:
The rays converge at a point or appear to diverge from a point lying on the focal plane.

45. Draw a ray diagram to illustrate the behaviours, of a parallel beam of rays incident on convex lens making some angle with principal axis. (AS5) 2 Marks
A:

46. Draw a figure to show the behaviour of a parallel beam of rays fall an a concave lens making some angle with principal axis. (AS5) 2 Marks
A:

47. Where does the image form when the object is at infinite distance from the convex lens? What are the characteristics of the image.  (AS1) 1 Marks
A:
A point size image is formed at focus.

48. Where does the image form when an object is placed beyond the centre of curvature on the principal axis of a convex lens? Write the characteristics of the image formed.                                                                                         (AS1) 2 Marks
A:
The image is formed on the principal axis between the points, F1 and C1. The image formed will be a real, inverted and diminished.

49. Draw the ray diagram showing the formation of image when the object is placed beyond the centre of curvature?                                               (AS5) 1 Mark
A:

50. Where does the image form when the object is placed at the centre of curvature (C2) of a convex lens? Write the characteristics of image? (AS1) 2 Marks
A:
The image is formed at centre of curvature (C1). The image formed will be a real, inverted and of the same size as that of the object.

51. Draw the figure to show the formation of image using a convex lens when the object is placed between centre of curvature and focal point. (AS5) 1 Mark
A:

52. Where does the image form when the object is placed at the focal point on principal axis of a convex lens. Draw the ray diagram. (AS5) 2 Marks
A:
The object when placed at F, Image will be formed at infinite distance.

53. Mention the characteristics of the image formed when the object is placed between focal point and optic centre. (AS1) 2 Marks
A:
We will get an image which is virtual, erect and magnified in this situation.

54. What do we call the image which we can see with our eye? (AS6) 1 Mark
A:
Virtual image.

55. Which type of image is formed by microscope? (AS6) 1 Mark
A:
Virtual image, which is magnified.

56. Where should we place the object on principal axis of a concave lens to get the image and where will the image formed? Write the characteristics of the image?   (AS1) 2 Marks
A:
Irrespective of the position of object, on the principal axis, we will get an erect, virtual image diminished in size between the focal point and optic centre for a concave lens.

57. Draw a ray diagram to show the formation of an image when an object is placed between C1 and F1 of a concave lens. (AS5) 2 Marks
A:

58. How does a convex lens behave when it is placed in a medium with refractive index less than the refractive index of the lens? (AS1) 1 Mark
A:
The convex lens behaves as a converging lens, if it is kept in a medium with refractive index less than of the lens.

59. How does a convex lens behave when it is places in a medium with greater refractive index than that of the lens? (AS1) 1 Mark
A:
It behaves like a diverging lens.

60. Write the list of the apparatus required to find the focal length of a convex lens. (AS3) 1 Mark
A:
A convex lens, V-stand, screen, candle.

61. Imagine what would have happened if the lens were not found? (AS2) 1Mark
A:
The manufacture of microscope, telescope would not be possible.

62.

Incident ray AB falls on a lens. The refracted ray BC is shown in figure.
Name the lens. (AS5) 1 Mark
A:
The lens is concave lens.

PROBLEMS - SOLUTIONS
1.
A Concave lens of focal length 15 cm forms an image 10 cm from the lens. How far the object placed from the lens? (AS1) 2 Marks
Sol: As per the given data
focal length (f) = -15 cm
image distance (v) = -10 cm
object distance (u) = ?

... u = -30 cm from the lens.

2. A 5 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 20 cm. The distance of the object from the lens is 30 cm. Find the nature, position and size of the image also find magnification. (AS1) 4 Marks
Sol: As per the given data
Object size h = +5 cm
Focal length f = 20 cm
Object distance u = -30 cm
Image distance v = ?
Image size (h') = ?

3. A Convex lens of focal length 10 cm is placed at a distance of 12 cm from a wall. Calculate the distance from the lens where an object be placed so as to form its distinct real image on the wall. (AS1) 2 Marks
Sol: As per the given data
f = +10 cm
v = +12 cm

... u = -60 cm.

4. For a plano convex lens. The radius or curvature of convex surface is 10 cm, and the focal length is 30 cm. Then find refractive index of the material of the lens. (AS1) 4 Marks
Sol: As per the given data
f = 30 cm
R1 = R = 10 cm
R2 = ∞

5. The refractive index of a lens is 1.5. An object is kept infront of the lens at a distance of 30 cm and image is formed at a distance of 20 cm. Find the focal length of lens. What is the nature of lens? If both curvatures are same, what is the radius of curvature?
(AS1) 4 Marks
Sol: As per the given data Object distance (u) = -30 cm
Image distance (v) = 20 cm
Focal length (f) = ?

... R = 12 cm
... Radius of curvature is 12 cm
... R1 = R2 = 12 cm

6. The radius of curvatures (R) of biconvex lens is same. An object is kept at center of curvature, the refractive index of material is 'n'. Lens is kept in air. (AS1) 4 Marks
a) What is the focal length?
b) Find out image distance?
c) Discuss the nature of image?
Sol: a) R1 = R2 = R
Refractive index = n

b) Image distance = v

c) The image distance is less than the object distance.

7. If the focal length of a glass lens is 50 cm, then find its power.
Sol: Focal length of lens f = 50 cm

... Power of lens = 2 Diaptors

8. If the focal length of a glass lens is 0.25 m, then find its power. (AS1) 2 Marks
Sol: Focal length of lens f = 0.25 m

... Power of a lens = 4 Diaptors.

9. The radius of curvature of two faces of a double convex lens are 10 cm, 15 cm and its focal length is 12 cm. Then determine the refractive index of the lens. (AS1) 4 Marks
Sol: As per the given data
f = +12 cm
R1 = 10 cm
R2 = -15 cm
Take the refractive index of air = 1

10. An object is placed on principle axis at a distance of 20 cm before a convex lens of focal length 10 cm. Find the nature of the image and its position. (AS1) 4 Marks
Sol: As per the given data
f = 10 cm
u = -20 cm
v = ?

... The nature of the image is real, inverted and of the same size as that of object.

11. Two thin lenses of powers +3.5 D and -2.5 D are placed in contact. Find the power and focal length of the lens combination. (AS1) 2 Marks
Sol: As per the given data
Here P1 = +3.5 D
P2 = -2.5 D
P = P1 + P2

= 3.5 - 2.5
= 1.0 D

12. What is the focal length of double concave lens kept in air with two spherical surfaces of radii R1 = 10 cm and R= 20 cm. Take refractive index of lens as n = 1.5. (AS1) 4 Marks
Sol: As per the given data
R= -10 cm
R2 = 20 cm
n = 1.5

13. Double - convex lenses are to be manufactured from a glass of refractive index 1.55, with both faces of the same radius of curvature. What is the radius of curvature required if the focal length is to be 10 cm? (AS1) 4 Marks
Sol: As per the given data
n = 1.55
R1 = R
R2 = -R
f = 10 cm

R = 11 cm

14. A Convex lense produces a real, inverted and 1.5 times magnified image at a distance of 15 cm from the lens. Calculate focal length of the lens. (AS1) 4 Marks
Sol: As per the given data
Magnification (m) = 1.5
Distance of the image from the lens (v) = 15 cm
Distance of the object from the lens (u) = ?
Focal length of the lens (f) = ?

As 'u' is always negative for a lens, therefore
u = -10 cm

Thus the local length of the lens is 6 cm.

15. An object 2 cm height is placed at a distance of 20 cm from the optical centre of a concave lens of focal length 10 cm. Calculate.
(i) the position of the image
(ii) the size of the image also
(iii) state the characteristics of the image. (AS1) 4 Marks
Sol. As per the given data
focal length of the lens (f) =-10 cm
object height (ho) = 2 cm
object distance (u) = -20 cm
image distance (v) = ?
image height (hi) = ?

Thus, the image is formed at a distance of 6.66 cm on the same side as the object.

Thus, the size of the image is 0.66 cm

(iii) The image is virtual, erect and diminished.

Posted Date : 15-11-2020

గమనిక : ప్రతిభ.ఈనాడు.నెట్‌లో కనిపించే వ్యాపార ప్రకటనలు వివిధ దేశాల్లోని వ్యాపారులు, సంస్థల నుంచి వస్తాయి. మరి కొన్ని ప్రకటనలు పాఠకుల అభిరుచి మేరకు కృత్రిమ మేధస్సు సాంకేతికత సాయంతో ప్రదర్శితమవుతుంటాయి. ఆ ప్రకటనల్లోని ఉత్పత్తులను లేదా సేవలను పాఠకులు స్వయంగా విచారించుకొని, జాగ్రత్తగా పరిశీలించి కొనుక్కోవాలి లేదా వినియోగించుకోవాలి. వాటి నాణ్యత లేదా లోపాలతో ఈనాడు యాజమాన్యానికి ఎలాంటి సంబంధం లేదు. ఈ విషయంలో ఉత్తర ప్రత్యుత్తరాలకు, ఈ-మెయిల్స్ కి, ఇంకా ఇతర రూపాల్లో సమాచార మార్పిడికి తావు లేదు. ఫిర్యాదులు స్వీకరించడం కుదరదు. పాఠకులు గమనించి, సహకరించాలని మనవి.