Class 10 Physics Light Important Questions

Very Short Answer Questions [1 marks]


PG logo with course.JPG1. Define lens.PG logo with course.JPG
Ans. A piece of optical material bounded by one or two spherical surfaces is called lens.

PG logo with course.JPG2. Why is a convex lens called converging lens? PG logo with course.JPG
Ans. It is because a parallel beam of light on passing through it converges at a point.

PG logo with course.JPG3. Define optical centre of a lens. PG logo with course.JPG
Ans. A point within the lens, where a line drawn through its aperture intersects the principal axis.

PG logo with course.JPG4. Define principal focus for a convex lens. PG logo with course.JPG
Ans. A point on the principal axis of a lens, where the rays coming parallel to the principal axis after refraction meet is called principal focus of the convex lens.

PG logo with course.JPG5. Define principal focus of a concave lens? PG logo with course.JPG
Ans. A point on the principal axis of a lens, where the rays coming parallel to the principal axis after refraction, appear to meet is called principal focus of the concave lens.

PG logo with course.JPG6. A virtual, erect and enlarged image is formed by a lens. Is the lens convex or concave? PG logo with course.JPG
Ans. The lens is convex lens.

PG logo with course.JPG7. Where will you place an electric lamp from a convex lens, so that a parallel beam of light comes out of it ? PG logo with course.JPG
Ans. The lamp should be placed at the principal focus of the lens.

PG logo with course.JPG8. A small object is placed in front of convex lens, when a real, inverted and enlarged image is formed on the other side of lens. Where is the object placed? PG logo with course.JPG
Ans. The object is between F and 2F of the convex lens.

PG logo with course.JPG9. Printed letters appear diminished when viewed through a lens. What is the nature of lens? PG logo with course.JPG
Ans. The lens is a concave lens.

PG logo with course.JPG10. A thin spherical lens has a focal length – 20 cm. What is the nature of lens? PG logo with course.JPG
Ans. The lens is a concave lens.

PG logo with course.JPG11. A thin spherical lens has radius of curvature 50 cm. What is its focal length? PG logo with course.JPG
Ans. F = R/2 = 25 cm

PG logo with course.JPG12. What do you understand by the term power of lens? PG logo with course.JPG
Ans. The reciprocal of focal length of a lens in metres, is called power of lens.

PG logo with course.JPG13. Name the unit in which power of lens is measured. PG logo with course.JPG
Ans. The power of lens is measured in dioptres.

PG logo with course.JPG14. The power of a lens is +1.5 D. Is the lens convex or concave? PG logo with course.JPG
Ans. It is a convex lens. [Note: Power of a convex lens is positive]

PG logo with course.JPG15. The power of a lens is –2 D. Is the lens converging or diverging? PG logo with course.JPG
Ans. It is a diverging lens. [Note: Power of a concave lens is negative]

PG logo with course.JPG16. P1 and P2 are the power of two thin lenses. What is the power P when both lenses are placed in contact with one another? PG logo with course.JPG
Ans. P = P1 + P2.

PG logo with course.JPG17. What do you understand by the term refractive index? PG logo with course.JPG
Ans. The ratio between the sine of angle of incidence (in air) to the sine of angle of refraction (in a denser medium) is called refractive index.

PG logo with course.JPG18. Refractive index of glass is 1.5. What do you understand from the statement? PG logo with course.JPG
Ans. It means that ratio of sine of angle of incidence (in air) to sine of angle of refraction (in glass) is 1.5.

PG logo with course.JPG19. At what angle a ray of light should strike the surface of glass, so that it does not suffer any refraction? PG logo with course.JPG
Ans. It should strike normally i.e., angle of incidence should be zero.

PG logo with course.JPG20. How is refractive index related to velocity of light in a medium and velocity of light in vacuum?PG logo with course.JPG
Ans.  Refractive index = Velocity of light in medium / Velocity of light in vacuum.

PG logo with course.JPG21. What do you understand from the term lateral displacement? PG logo with course.JPG
Ans. Lateral displacement is perpendicular shift in the path of the incident ray, while emerging out from an optical slab.

PG logo with course.JPG22. Will the lateral displacement increase/decrease, if glass block is made thicker?
Ans. The lateral displacement will increase.

PG logo with course.JPG23. How is the focal length of a spherical mirror related to its radius of curvature? PG logo with course.JPG
Ans. Focal length is half of the radius of curvature.

PG logo with course.JPG24. Why is a convex mirror is called diverging mirror? PG logo with course.JPG
Ans. It is because, a parallel beam of light after reflection from it, diverges outward.

PG logo with course.JPG25. Why is a concave mirror is called converging mirror? PG logo with course.JPG
Ans. It is because, a parallel beam of light after reflection from it, converges at one point.

PG logo with course.JPG26. Is the image formed in a convex mirror always virtual? PG logo with course.JPG
Ans. Yes, image formed by convex mirror is always virtual.

PG logo with course.JPG27. Where is the image formed in a concave mirror, when the object is between infinity and centre of curvature? PG logo with course.JPG
Ans. The image is formed between the principal focus and centre of curvature, in front of the concave mirror.

PG logo with course.JPG28. Where is the image formed in a convex mirror, when the object is anywhere in front of it? PG logo with course.JPG
Ans. The image is formed between the pole and principal focus, behind the convex mirror.

PG logo with course.JPG29. No matter how far you stand from a spherical mirror, your image appears always erect. What is the kind of spherical mirror? PG logo with course.JPG
Ans. The spherical mirror is a convex mirror.

PG logo with course.JPG30. A spherical mirror has focal length of – 40 cm. What is the kind of mirror? PG logo with course.JPG
Ans. The spherical mirror is a concave mirror.

PG logo with course.JPG31. What is the focal length of a plane mirror? PG logo with course.JPG

Ans. Focal length of a plane mirror is infinity (∞).

PG logo with course.JPG32. How does the frequency of a beam of ultraviolet light change when it does from air into glass? PG logo with course.JPG

Ans. Frequency of ultraviolet light does not change.

PG logo with course.JPG33. What is the focal length of a plane mirror? PG logo with course.JPG
Ans. The focal length of a plane mirror is infinite.

PG logo with course.JPG34. When light undergoes refraction at the surface of separation of two media, what happens to its wavelength? PG logo with course.JPG
Ans. Wavelength changes.

PG logo with course.JPG35. When light undergoes refraction, what happens to its frequency? PG logo with course.JPG
Ans. Frequency does not change.

PG logo with course.JPG36. How does a focal length of convex lens change if monochromatic red light is used instead of monochromatic blue light? PG logo with course.JPG
Ans. Because red light and blue light both has different refractive indices.

PG logo with course.JPG37. If the power of a lens is + 5 dioptre, what is its focal length? PG logo with course.JPG
Ans. Focal length of lens = 1/5 m = 0.2 m = 200 mm

PG logo with course.JPG38. Draw a ray diagram to show reflection of an incident ray parallel to principal axis by a convex mirror. PG logo with course.JPG

Ans. Given the end of this page

PG logo with course.JPG39. What is the minimum distance between an object and its real image in case of a concave mirror ? PG logo with course.JPG

Ans. Zero, when object is at centre of curvature, its real image is also formed at the same point.

PG logo with course.JPG40. What are the two factors on which the lateral displacement of an emergent ray from a glass slab depends ?  PG logo with course.JPG
Ans. (i) Angle of incidence (ii) Thickness of glass slab

PG logo with course.JPG41. Between which two points related to a concave mirror should an object be placed to obtain on a screen an image twice the size of the object? PG logo with course.JPG
Ans. Between centre of curvature and the principal focus.


Q.38

1 thought on “Class 10 Physics Light Important Questions

Leave a Reply

We Need Your Support!

We all are helping students with free educational resources.

Your little support can make a big difference. As little as INR 5 will help.

Donate Now

Assertion Reason Questions for Class 10 Social Science Geography

%d bloggers like this:
search previous next tag category expand menu location phone mail time cart zoom edit close