Ans: The focus of convex mirror is situated behind it.
2. For what position of an object, a concave mirror forms an enlarged virtual image?
Ans: Object between pole (P) and focus (F) of the concave mirror.
3. If the focal length of a concave mirror is 25cm. What is its radius of curvature?
Ans: Focal length = Radius of curvature / 2
25 = R / 2
R = 25 X 2 = 50cm.
4. A ray of light falls on a mirror normally. What are the values of angle of incidence and the angle of
reflection?
Ans: Both angle of incidence and the angle of reflection are zero.
5. What is the focal length of a plane mirror?
Ans: Infinite.
6. Which spherical mirror is called a divergent mirror?
Ans: A convex mirror is called a divergent mirror.
7. What is the angle of incidence, when a ray of light falls on the spherical mirror from its centre of curvature?
Ans: The angle of incidence is zero, when a ray of light falls on the spherical mirror from its centre of
curvature.
8. Name the type of mirror that always forms a virtual image for a real object?
Ans: Convex Mirror.
9. State the relation between radius of curvature and focal length of spherical mirrors.
Ans: Radius of curvature = 2 X focal length.
R = 2f.
10. Which of the two is a diverging lens? Convex lens (or) Concave lens.
Ans: Concave lens.
11. If an object is placed at a distance of 10cm in front of a plane mirror, how far would it be from its image?
Ans: The object would be at a distance of 20cm from its image.
12. Name the physical quantity which remains the same when light goes from one medium to another?
Ans: Frequency of light.
13. Define power of a lens.
Ans: The reciprocal of the focal length of the lens is called power of a lens. P = 1/f
14. Calculate the power of a convex lens of focal length 25cm?
Ans: Focal length f = 25cm.
Power = 1/.25 = 100/25 = +4D.
15. Name the phenomenon responsible for the following affect.
Ans: When we sit in front of a plane mirror and write with our right hand, it appears in the mirror that we are
writing with the left hand.Ans: Lateral Inversion
16. Define Refractive Index
Ans: It is the ratio of speed of light in vacuum to the speed of light in medium is called Refractive index.
17. Why is the convex lens also known as a converging lens?
Ans: A convex lens is also known as a converging lens because it converges a parallel beam of light raying
passing through it.
18. Give the ratio of velocities of two light waves travelling is vacuum and having wave lengths 4000A and
8000A.
Ans: In Vacuum, light of all the wave lengths travel with the same velocity i.e. 3 X 108 m/sec.
19. For what angle of incidence, the lateral shift produced by parallel sided glass plate is zero?
Ans: For i = 0.
20. What are the factors on which the lateral shift depends?
Ans: Thickness of the refracting medium, angle of incidence and its refractive index.
21. What is the power of a plane glass plate?
Ans: Zero.
22. An object is placed at the focus of a concave lens. Where will its image be formed?
Ans: The rays will appear to come from infinity. Therefore, a virtual image will be formed at infinity.
23. What is the unit of power of a lens?
Ans: Dioptre.
24. Write some applications of concave and convex lens
Ans: Some uses of concave lens:
1. In spectacles for eyes suffering from myopia.
2. In the lens combination of camera, telescope.
3. In door hole lenses.
Some uses of convex lens:
1. In spectacles for eyes suffering from hypermetropia.
2. In the lens combination of camera, telescope, microscope
3. It is also used as a magnifying lens.
25. What is the value of refractive index of air?
Ans: One
26.A ray of light passes through an equilateral glass prism, such that angle of incidence is equal to the angle of emergence. If the angle of emergence is ¾ times the angle of prism,calculate the refractive index of glass prism?
Solution:
As the prism is an equilateral one A = 600
Also I = e = ¾ A = ¾ X 60 0 = 45 0
Further as the angle of incidence is equal to the angel of emergence, the prism is in minimum deviation position. We know that when the prism is placed in minimum deviation position r = A/2 = 300 and I = 450
N = Sin i/Sin r = 1Ö2 X 2 = Ö2.
For Extra score study material visit :
10th Science - Light Refraction and Refraction Explanation View
10th Light – Reflection and Refraction Key concepts and terms View
X Physics Reflection and Refraction Solved questions-1 View
VERY SHORT QUESTIONS CARRYING 1 MARK EACH. View
Test your self
1. How does the frequency of a beam of ultraviolet light change when it goes from air into glass ? [Delhi
2001]
2. What is the focal length of a plane mirror ?[Delhi 2001C]
3. When light undergoes refraction, what happens to its frequency ? [AI 2000C]
4. When light undergoes refraction at the surface of separation of two media, what happens to its wavelength ? [AI 2000C]
5. The image of an object formed by a lens on the screen is not in sharp focus. Suggest a method to get clear focussing of the image on the screen without disturbing the position of the object, the lens or the screen. [Delhi 1998]
6. Which of the two main parts of an optical fibre has a higher value of refractive index ? [Delhi 2004C]
7. When a ray of light is passed through a prism, under what condition will the angle of incidence be equal to the angle of emergence ? [AI 2004C]
8. An object is placed at the focus of a concave lens. Where will its image be formed ? [AI 2003]
9. A lens of glass is immersed in water. What will be its effect on the power of the lens ? [AI 2003]
10. Vehicles moving in foggy weather use yellow colour headlights. Why ? [AI 2002C]
11. When a ray of light is passed through a prism, under what condition will the angle of incidencebe equal to the angle of emergence ? [AI 2004C]
12.A liquid of refractive index 1.5 is poured into cylindrical jar of radius 20cm up to height of 20 cm. A small bulb is lighted at the center of the bottom of the jar. Find the area of liquid surface thorough which the light of the bulb passes into air.