GIST OF THE CHAPTER Light Refraction and Refraction
1. The first theory of light was put forward by Newton. This theory treats light as a particle called corpuscle. 2. We can say that light propagates as a wave and is emitted and absorbed as a particle. 3. One may regard light as having dual nature. 4. Maxwell proved that light has wave nature; it is an electromagnetic transverse wave, which does not require medium to propagate. 5. The speed of light in air is a universal constant. It has a value of 3x108m/s. 6. Light gets reflected when it falls on polished surface; like mirror. 7. Light suffers refraction when it travels from one medium to another. 8. There is a change in the wavelength of light when it moves from one medium to another. 9. The image is unmagnified, virtual and erect in a plane mirror. 10 Focal length of a plane mirror is infinity. 11. Power of a plane mirror is zero.' 12. It should be noted that, if the spherical lenses are surrounded by a material with a refractive index greater than that of the lens, the convex lens gets converted into a concave lens or vice-versa. FORMULAE f = R/2 1 / v + 1 / u = 1 / f = 2 /R M = h2 /h1 = -v/u n = c/v 1n2 = 1/2n1 1n2 = n2/n1= sin i/sin r a n w = x/y 1/v –1/u = 1/f m =I/O = h2 /h1 = v/u P= 1/f metre P = p1 + p2 + p3 + ……. VERY SHORT QUESTIONS CARRYING 1 MARK EACH. 1. Out of convex mirror and concave mirror, whose focus is situated behind the mirror? 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. Why the stars appear to twinkle? Ans: The twinkling of a star is due to the atmospheric refraction of star’s light. 25. What is the value of refractive index of air? Ans: One More study material visit : 10th Science - Light Refraction and Refraction10th Light – Reflection and Refraction Key concepts and terms X Physics Reflection and Refraction Solved questions-1
1 Comment
sumit
6/11/2011 12:13:00 pm
very useful
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