WBCHSE Class 12 Physics Refraction Of Light At Spherical Surface Lens Very Short Answer Questions

Refraction Of Light At Spherical Surface Lens Very Short Questions And Answers

Question 1. Air bubbles are formed in water. Will it behave like a converging or a diverging lens?
Answer: Like advertising lens

Question 2. Under what conditions will the first and the second principal focal lengths of a lens be equal?
Answer: If the same medium exists on both sides of the lens

Question 3. For which type of lens is the optical center situated outside the lens?
Answer: For convexo-concave and concavo-convex lens]

Question 4. Where is -the optical center of a lens situated if only one surface of it is spherical?
Answer: At the intersecting point of the principal axis and the spherical surface

Question 5. The optical center of a lens may lie outside the lens Is the statement true or false?
Answer: True

Question 6. A portion of a lens is broken. Will we get a complete image of an object with such a lens?
Answer: Yes; but the intensity of the image will be lesser

WBBSE Class 12 Refraction of Light VSAQ

Question 7. Can a lens be used in the medium in which it is made?
Answer: No

Question 8. If the refractive index of the material of a lens is equal to that of its surrounding medium what will happen?
Answer: The lens, will behave as a plane glass plate]

Question 9. A convex lens is placed on a plane mirror. 1fa point source of light is placed at the focus of the lens where Will the image of the source of light be formed?
Answer: At the same focus

Question 10. Where does the optical center of a convexo-concave lens
Answer: Outside the lens

Question 11. Which principal focus is effective for the formation of images?
Answer: Secondary

Question 12. When will the image of an object formed by a convex lens be virtual?
Answer: If the object distance is less than

Question 13. If an object is placed at the focus of a convex lens where will its image be formed? .
Answer: At infinity

Question 14. Where should an object be placed concerning a convex lens to get an image of equal size?
Answer: At a distance of 2f from the lens

Question 15. Half of a biconvex lens is covered with black paper. Will a complete image of any object be formed?
Answer: Yes

Question 16. What is the nature of the image formed by a concave lens? Which mirror forms images of the same nature?
Answer: Virtual, Convex

Question 17. A concave lens has a focal length/. Where will the image be formed if an object is kept in the focus?
Answer: Towards the object at a distance

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Question 18. If the distances of a real object and its real image in the case of a convex lens are u and v respectively, what will be the nature of the v~u graph?
Answer: Rectangular hyperbola

Question 19. If the distances of a real object and its real image in the case of a convex lens are u and v respectively, what will be the nature of the graph?
Answer: Straight Line

Question 20. Magnification of a concave lens is always less than 1 is this statement true or false?
Answer: True

Question 21. What should be the minimum distance between a screen and an object such that a convex lens placed in between them can form a real image?
Answer: 4 times the focal length of the lens

Question 22. What type of image does a convex lens form if the object is virtual?
Answer: Real

Question 23. What is the minimum distance between an object and its real image for a convex lens of focal length 15 cm?
Answer: 60 cm

Very Short Answer Questions on Spherical Lenses

Question 24. What should be the position of an object relative to the biconvex lens so that this lens behaves like a magnifying glass?
Answer: Between the optical center and focus of the lens

Question 25. If a biconvex lens of focal length f is cut into two halves along its principal axis, what will be the focal length of each half?
Answer: f

Question 26. A convex lens is placed in contact with a concave lens of greater focal length. How this lens combination will act?
Answer: It will act as a convex lens

Question 27. Two thin convex lenses of equal focal length (f) are kept in contact with each other co-axially. What will be their equivalent focal length?
Answer: \(\frac{f}{2}\)

Question 28. A thin convex lens and a thin concave lens each of focal length f are kept in contact with each other. What will be the equivalent focal length of the combination?
Answer: Infinity

Question 29. What is the relation of the radii of curvature of a lens with its power?
Answer: P = \((\mu-1)\left(\frac{1}{r_1}-\frac{1}{r_2}\right)\)

Question 30. What is the S1 unit of power of a lens?
Answer: Dioptre or m^-1

Question 31. Two lenses of powers 0.5 D and 0.2 D are kept in contact with each other. What is the equivalent power of this combination of lenses?
Answer: 0.7D

Question 32. What is the focal length of a lens of power 2.5 D?
Answer: 40 cm

Common VSAQs on Laws of Refraction

Question 33. A glass lens is immersed in water. How is the power of the lens
Answer: The focal length will increase and the power will decrease

Question 34. If two convex lenses of powers and D are kept in contact with each other, what will be the equivalent power of the lens combination? affected?
Answer: D1+D2

Question 35. When the radii of curvature of the biconvex or biconcave lens increases, how is the power affected?
Answer: Power decreases

Question 36. A uniform biconvex lens is cut into two halves along its principal axis. If the original lens power is 2D, what will be the power of each of the two haves?
Answer: 2D

Question 37. What is the power of the lens of a sunglass?
Answer: Zero

Question 38. Will the focal length and power of a lens increase or decrease when it is immersed in water from air?
Answer: Focal length increases but power decreases

Question 39. A biconvex lens is cut into two halves perpendicular to its principal axis. If the power of the original lens is 4 D, what will be the power of each half?
Answer: 2D

Question 40. If the radii of curvature of the two surfaces of a concavoconvex lens are equal, what will be the focal length and the
Answer: Infinite, zero

Question 41. What will be the focal length and power of a plane glass
Answer: Infinite, zero

Practice VSAQs on Image Formation by Lenses

Question 42. What is the focal length and power of a parallel glass slab?
Answer: Infinity and zero respectively

Question 43. What type of lens is used in the camera?
Answer: Single or a combination of convex lenses

Question 44. What is the nature of the image formed in the camera?
Answer: Real and inverted

Question 45. If the diaphragm of a camera increases by f, how is the image affected?
Answer: Image becomes distinct.

Question 46. Under what condition will a concave lens behave as a convex
Answer: The lens has to be kept in a medium that is optically denser than the material of the lens.

Question 47. What type of lens is an air bubble in water?
Answer: The shape of an air bubble in water is very near to that of a thick biconvex lens. But as the refractive index of water is greater than that of air, the bubble acts as a concave lens.

Conceptual VSAQs on Focal Length and Magnification

Question 48. If half a portion of a biconvex lens is covered by black paper, then state whether the formed image is complete or not.
Answer: A complete image is formed for refraction by the remaining half portion of the lens. But in this case, the brightness of the image is decreased

Question 49. 1n which case the focal length first and second principal focus of a lens will be equal?
Answer: If the surrounding medium of a lens is the same then the focal length of the first and second principal focus of a lens becomes equal

Question 50. Explain what happens when the aperture of a camera lens is reduced by Wring
Answer:

• If the aperture of a lens is reduced the marginal rays are obstructed. Only the axial rays after refraction through the lens form the image.
• So, the image is free from spherical aberration and is distinct.