{"id":1603,"date":"2020-07-10T19:38:48","date_gmt":"2020-07-10T19:38:48","guid":{"rendered":"https:\/\/murreeroad.org\/physics10\/?p=1603"},"modified":"2020-08-15T18:50:28","modified_gmt":"2020-08-15T18:50:28","slug":"physics10-chapter12-lq","status":"publish","type":"post","link":"https:\/\/murreeroad.org\/physics10\/physics10-chapter12-lq\/","title":{"rendered":"Physics10 Chapter12-lq"},"content":{"rendered":"

<\/a>Chapter 12 Long Questions<\/h2>\n

Q. 12.1. What do you understand by reflection of light? Draw a diagram to illustrate reflection at a plane surface.<\/a><\/strong>
\nQ. 12.2. Describe the following terms used in reflection:<\/a><\/strong>
\n\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0<\/strong>(i) normal (ii) angle of incidence (iii) angle of reflection<\/strong><\/a>
\nQ.12.3. State laws of reflection. Describe how they can be verified graphically.<\/a><\/strong>
\nQ. 12.4. Define refraction of light. Describe the passage of light through parallel-sided transparent material.<\/a><\/strong>
\nQ.12.5. Define the following terms used in refraction:<\/a><\/strong>
\n\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 <\/strong>\u00a0(i) angle of incidence (ii) angle of refraction<\/strong><\/a>
\nQ.12.6. What is meant by refractive index of a material? How would you determine the refractive index of a rectangular glass slab?<\/a><\/strong>
\nQ.12.7. State the laws of refraction of light and show how they may be verified using rectangular glass slab and pins.<\/a><\/strong>
\nQ.12.8. What is meant by the term total internal reflection?<\/a><\/strong>
\nQ.12.9. State the conditions for total internal reflection.<\/a><\/strong>
\nQ.12.10. What is critical angle? Derive a relationship between the critical angle and the refractive index of a substance.<\/a><\/strong>
\nQ.12.11. What are optical fibers? Describe how total internal reflection is used in light propagating through optical fibers.<\/a><\/b>
\nQ.12.12. Define the following terms applied to a lens:<\/a><\/strong>
\n\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 (i) principal axis (ii) optical center (iii) focal length<\/a><\/b>
\nQ.12.13. What is meant by the principal focus of a (a) convex lens (b) concave lens? Illustrate your answer with ray diagrams.<\/a><\/strong>
\nQ.12.14. Describe how light is refracted through convex lens.<\/a><\/strong>
\nQ.12.15. With the help of a ray diagram, how you can show the use of thin converging lens as a magnifying glass.<\/a><\/strong>
\nQ.12.16. A coin is placed at a focal point of a converging lens. Is an image formed? What is its <\/a><\/strong>nature?<\/strong><\/a>
\nQ.12.17. What are the differences between real and virtual images?<\/a><\/strong>
\nQ.12.18. How does a converging lens form a virtual image of a real object? How does a diverging lens can form a real image of a real object?<\/a><\/strong>
\nQ.12.19. Define power of a lens and its units.<\/a><\/strong>
\nQ.12.20. Describe the passage of light through a glass prism and measure the angle of deviation.<\/a><\/strong>
\nQ.12.21. Define the terms resolving power and magnifying power.<\/a><\/strong>
\nQ.12.22. Draw the ray diagrams of (i) simple microscope (ii) compound microscope (iii) refracting telescope<\/a><\/strong>
\nQ.12.23. Mention the magnifying powers of the following optical instruments:<\/a><\/strong>
\n\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0(i) simple microscope (ii) compound microscope (iii) refracting telescope<\/a><\/strong>
\nQ.12.24. Draw ray diagrams to show the formation of images in the normal human eye.<\/a><\/strong>
\nQ.12.25. What is meant by the terms nearsightedness and farsightedness? How can these defects be corrected?<\/a><\/strong><\/p>\n

CONCEPTUAL QUESTIONS<\/strong><\/p>\n

Q.12.1 A man raises his left hand in a plane mirror, the image facing ‘him is raising his right hand. Explain why.<\/a><\/strong><\/p>\n

Q.12.2 In your own words, explain why light waves are refracted at a boundary between two materials.<\/a><\/strong><\/p>\n

Q.12.3 Explain why a fish under water appears to be at a different depth below the surface than it actually is. Does it appear deeper or shallower?<\/a><\/strong><\/p>\n

Q.12.4\u00a0 Why or why not concave mirrors are suitable for makeup?<\/a><\/strong><\/p>\n

Q.12.5. Why is the driver’s side mirror in many cars convex rather than plane or concave?<\/a><\/strong><\/p>\n

Q.12.6. When an optician’s testing room is small, he uses a mirror to help him test the eyesight of his patients. Explain why.<\/a><\/strong><\/p>\n

Q.12.7. How does the thickness of a lens affect its focal length?<\/a><\/strong><\/p>\n

Q.12.8. Under what conditions will a converging lens form a virtual image?<\/a><\/strong><\/p>\n

Q.12.9. Under what conditions will a converging lens form a real image that is the same size as the object?<\/a><\/strong><\/p>\n

Q.12.10. Why do we use refracting telescope with large objective lens of large focal length?<\/a><\/strong><\/p>\n

<\/a>Q. 12.1. What do you understand by reflection of light? Draw a diagram to illustrate reflection at a plane surface.<\/strong><\/p>\n

Answer: <\/strong>When light ray is completely returns- back into some medium after felling
\nfrom a polished surface is called “reflection of light”<\/p>\n

Draw:<\/strong><\/p>\n

\"\"
\n<\/a>Q. 12.2. Describe the following terms used in reflection:<\/strong>
\n(i) normal (ii) angle of incidence (iii) angle of reflection<\/strong><\/p>\n

Answer: <\/strong><\/p>\n

Normal:<\/u><\/strong><\/p>\n

‘The perpendicular drawn on the reflecting plane, at point of incidence of ray of light as called “normal”.<\/p>\n

Angle of Incidenc<\/u>e <\/u><\/strong><\/p>\n

The angle between incident ray and normal is called angle of incidence.<\/p>\n

Angle of reflection <\/u><\/strong><\/p>\n

The angle between reflected ray and normal is called angle of reflection.<\/a><\/p>\n

Q.12.3. State laws of reflection. Describe how they can be verified graphically.<\/strong><\/p>\n

Answer: <\/strong>There are two laws of reflection of light.<\/p>\n

a. The incident ray the normal and the reflected ray at the point of incidence all lie in the same plane.<\/p>\n

b. The angle of incidence is equal to the angle of reflection.<\/p>\n

\"\"
\n<\/a>Q. 12.4. Define refraction of light. Describe the passage of light through parallel-sided transparent material.<\/strong><\/p>\n

Answer:<\/strong> In physics,\u00a0refraction<\/b>\u00a0is the change in direction of a wave passing from one medium to another or from a gradual change in the medium.\u00a0Refraction of light<\/b>\u00a0is the most commonly observed phenomenon, but other waves such as sound waves and water waves also experience\u00a0refraction<\/b>.<\/p>\n

If a ray of\u00a0light\u00a0hits the surface of a sheet of glass, some\u00a0light\u00a0will be reflected\u00a0by\u00a0the surface of the glass. However, much of the\u00a0light\u00a0will\u00a0pass through\u00a0the glass, because glass\u00a0is transparent. This bending of a ray of light\u00a0when it\u00a0passes from\u00a0one substance into\u00a0another\u00a0substance\u00a0is\u00a0called\u00a0refraction.<\/a>
\nQ.12.5. Define the following terms used in refraction:<\/strong>
\n(i) angle of incidence (ii) angle of refraction<\/strong><\/p>\n

Answer:<\/strong><\/p>\n

 <\/p>\n

(i) angle of incidence\"\"<\/strong><\/p>\n

The angle shown in the figure between incident ray (AO) and the normal (ON) is called angle of incident which is denoted by <AON = < \u03b81<\/sub><\/p>\n

(ii) angle of refraction<\/strong><\/p>\n

The angle between the reflected ray (OB) and the normal (ON) is called angle of reflection and is denoted by <ONB = < \u03b82<\/sub><\/a>
\nQ.12.6. What is meant by refractive index of a material? How would you determine the refractive index of a rectangular glass slab?<\/strong><\/p>\n

Answer: <\/strong>The ratio of sine of angle of incidence to the angle of refraction is called refractive index the refractive index of a glass slab is determined experimentally by using formula.<\/p>\n

Refractive index = sin \u03b81<\/sub> \/ sin \u03b82<\/sub><\/a>
\nQ.12.7. State the laws of refraction of light and show how they may be verified using rectangular glass slab and pins.<\/strong><\/p>\n

Answer:<\/strong><\/p>\n

1s<\/sup>t<\/sup> Law \u00a0\u00a0<\/strong>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 .<\/p>\n

It states that incident ray, normal and refracted ray lie in same plane.
\n2nd<\/sup> Law<\/strong><\/p>\n

It states that ratio of sine of angle of incidence to the sine of angle of refraction is constant (Snell’s law) .<\/a><\/p>\n

Q.12.8. What is meant by the term total internal reflection?<\/strong><\/p>\n

Answer: <\/strong>When a light ray is incident upon the separating surface, coming from denser medium for which angle of reflection in rare medium is greater than 90\u00b0 , then its is called total internal reflection.<\/a><\/p>\n

Q.12.9. State the conditions for total internal reflection.<\/strong><\/p>\n

Answer: <\/strong>The following are conditions of total internal reflection.<\/p>\n

(i) \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 The incident ray should come from denser medium at angle of incidence greater then critical angle.<\/p>\n

(ii) \u00a0\u00a0\u00a0\u00a0\u00a0 The totally reflected ray is received in the same denser medium.<\/a><\/p>\n

Q.12.10. What is critical angle? Derive a relationship between the critical angle and the refractive index of a substance.<\/strong><\/p>\n

Answer: Critical angle<\/strong><\/p>\n

The critical angle is defined as the angle of incidence that provides an angle of refraction of 90-degrees. Make particular note that the critical angle is an angle of incidence value. For the water-air boundary, the critical angle is 48.6-degrees.<\/p>\n

Relation Between Critical Angle<\/b>\u00a0And\u00a0Refractive Index<\/b>. <\/strong>In Optics, The\u00a0angle\u00a0of incidence to which the\u00a0angle\u00a0of\u00a0refraction\u00a0is 900<\/sup>\u00a0is called\u00a0critical angle. The ratio of velocities of a light ray in the air to the given medium is\u00a0refractive index.<\/a>
\nQ.12.11. What are optical fibers? Describe how total internal reflection is used in light propagating through optical fibers.<\/b><\/p>\n

Answer: Optical fibers: <\/b><\/strong>It is a hair size thread made up of glass for plastic through which light can be traveled.<\/p>\n

a. The inner part of fiber optic is called core that carries light.<\/p>\n

b. The outer part is concentric shell caused cladding.<\/p>\n

Total internal reflection used in fiber optics<\/strong><\/p>\n

When light traveling in an optically dense medium hits a boundary at a steep angle (larger than the\u00a0critical angle\u00a0for the boundary), the light is completely reflected. This is called total internal reflection. This effect is used in optical fibers to confine light in the core.<\/a><\/p>\n

Q.12.12. Define the following terms applied to a lens:<\/strong>
\n(i) principal axis (ii) optical center (iii) focal length<\/b><\/p>\n

Answer:<\/strong><\/p>\n

(i) Principal axis <\/u><\/strong><\/p>\n

The line passing through pole and focal point is called principle axis of lone.<\/p>\n

(ii)\u00a0 Optical <\/strong>center<\/b><\/p>\n

The central symmetric point of a lens is called optical center.<\/p>\n

(iii) Focal length \u00a0\u00a0 <\/strong><\/p>\n

The distance between focal point and optical center of lens is called its focal length.<\/a><\/p>\n

Q.12.13. What is meant by the principal focus of a (a) convex lens (b) concave lens? Illustrate your answer with ray diagrams.<\/strong><\/p>\n

Answer:<\/strong><\/p>\n

(a) Convex lens: <\/strong>The principal focus of a convex lens is defined as the point on which the principal axis of the light is parallel to the principal axis that converges after the refraction from the lens.<\/p>\n

b) Concave lens: <\/strong>The\u00a0principal focus\u00a0of\u00a0concave lens\u00a0is when the light rays\u00a0get\u00a0diverged and appear to form a single point.<\/p>\n

Ray Diagrams:<\/strong><\/p>\n

\"\"
\n<\/a>Q.12.14. Describe how light is refracted through convex lens.<\/strong><\/p>\n

Answer: <\/strong>A convex lens is a system of two prisms placed base to base as shown in Convex lens bends the light towards the principal axis that is towards thickest pan of the lens after refraction. Rays of\u00a0light\u00a0that pass\u00a0through\u00a0the\u00a0lens\u00a0are brought closer together (they converge). A\u00a0convex lens\u00a0is a\u00a0converging lens. When parallel rays of\u00a0light\u00a0pass\u00a0through\u00a0a\u00a0convex lens\u00a0the\u00a0refracted\u00a0rays converge at one point called the principal focus.<\/a><\/p>\n

Q.12.15. With the help of a ray diagram, how you can show the use of thin converging lens as a magnifying glass.<\/strong><\/p>\n

Answer: <\/strong>A magnifying glass is a convex lens used to make an object appear much larger than it actually is. This works when the object is placed at a distance less than the focal length from the lens. The image is:<\/span><\/p>\n