A. Very-Short-Answer Questions 1. From which surface of a mirror-the polished surface or the silvered surface-does most of the light reflect? 2. In which kinds of mirrors-plane, concave or convex-can you get a virtual image of an object placed in front of it? 3. What is the principal axis of a spherical mirror? 4. A concave mirror forms a real image of the same size as that of the object. Where is the object placed? 5. Can a convex mirror form a real image of an object? 6. A ray ACB is incident on a spherical mirror whose centre of curvature is C. In which direction will it reflect? 7. What is the sign of the object-distance u when an object is placed before a concave mirror? 8. Where can the position of an object be if a concave mirror forms its erect and virtual image? 9. A mirror has focal length f = +10 cm. Is it convex or concave? 10. What are the values of the angle of incidence and the angle of reflection for normal incidence on a plane mirror? 11. In the diagram, the ray is incident parallel to the principal axis. Redraw the diagram, showing the reflected B. Short-Answer Questions 1. What is silvering of a mirror? 2. Write the two laws of reflection of light. 3. What do you understand by the radius of curvature of a spherical mirror? 4. What is the difference between a real image and a virtual image? 5. Draw a diagram showing the pole, focus, centre of curvature and principal axis of a concave mirror. 6. Convex mirrors are used as rear-view mirrors in scooters, motorcycles, etc. Explain why. 7. Draw ray diagrams to show the formation of images when an object is placed (a) between the pole and focus, and (b) between the centre of curvature and focus. C. Long-Answer Questions 1. Describe a method to measure the focal length of a concave mirror. 2. Write the sign convention used for spherical mirrors. 3. By drawing a neat ray diagram, show the formation of the image of a point object placed above the principal axis of a convex mirror. Explain the construction.
Answers
A. Very-Short-Answer Questions
1. From which surface of a mirror-the polished surface or the silvered surface-does most of the light reflect?
ANS. The most of the light is reflected by the silvered surface of the mirror.
• There are two basic layers of a traditional mirror.
1) polished glass surface. (External)
2) silvered surface. (Internal)
• The light rays are mostly reflected by the internal layer of the mirror.
• Now,more than 95% of the light rays are reflected by the silvered surface of the mirror and less than 5% of the light rays is reflected by the polished glass surface of the mirror.
2. In which kinds of mirrors-plane, concave or convex-can you get a virtual image of an object placed in front of it?
ANS. convex and plane mirror always give you virtual image. however concave give you virtual, when object is between focus and pole .
3. What is the principal axis of a spherical mirror?
ANS. The Imaginary straight line passing through the pole and the centre of curvature of a spherical mirror is called the principal axis of a spherical mirror.
4. A concave mirror forms a real image of the same size as that of the object. Where is the object placed?
ANS. A concave mirror forms a real image of the same size as that of the object . ... When the object is located at the center of curvature, the image will also be located at the center of curvature. In this case, the image will be inverted,real and of same size.
5. Can a convex mirror form a real image of an object?
ANS. convex mirrors can produce real images as well. If the object is virtual, i.e., if the light rays converging at a point behind a plane mirror (or a convex mirror) are reflected to a point on a screen placed in front of the mirror, then a real image will be formed.
6. A ray ACB is incident on a spherical mirror whose centre of curvature is C. In which direction will it reflect?
ANS. The reflected ray will retrace the incident ray because the incident is coming through the principal axis.
7. What is the sign of the object-distance u when an object is placed before a concave mirror?
ANS. Nagative sign (-)
8. Where can the position of an object be if a concave mirror forms its erect and virtual image?
ANS. Object should be places between focus and pole of a mirror to get erect and virtual mirror.
9. A mirror has focal length f = +10 cm. Is it convex or concave?
ANS. It is convex mirror.
10. What are the values of the angle of incidence and the angle of reflection for normal incidence on a plane mirror?
ANS. For a plane mirror the angle of incidence and angle of reflection is same. So for normal incidence the angle of incidence with the normal is 0 degree and therefore the angle of reflection also.
Answer:
1 .
Ans . In order to avoid this, ordinary mirrors are made by coating a thin layer of silver metal or mercury on one side of a plane glass sheet and this silver layer is protected by applying a coat of red paint over it. Hence, the black silvered surface of a plane mirror reflects most of the light incidents on it.
2.
Ans. convex and plane mirror always give you virtual image. however concave give you virtual, when object is between focus and pole . plane mirror and convex mirror give virtual image where as concave give virtual image when object is Focus and pole.
3.
Ans . The principal axis of a spherical mirror is a line going through the center of the mirror that is exactly perpendicular (sometimes said "normal") to the surface of the mirror. By definition, a spherical mirror is rotationally symmetrical around its principal axis.
4.
Ans. A concave mirror forms a real image of the same size as that of the object . ... When the object is located at the center of curvature, the image will also be located at the center of curvature. In this case, the image will be inverted,real and of same size.
5.
Ans. Convex mirrors will only do this when the object is right on the mirror surface. ... Plane mirrors and convex mirrors only produce virtual images. Only a concave mirror is capable of producing a real image and this only occurs if the object is located a distance greater than a focal length from the mirror's surface.
6.
Ans. Any ray which passes through the centre of curvature is incident on a spherical mirror will retrace its path , that is pass again through the centre of curvature . So the ray will go back along the path ACB.
7.
Ans. The concave mirror forms a virtual and erect image only when the object is placed between the Focus and the pole of the mirror.
9.
Ans It is a convex mirror because focal length is always positive in convex mirror and negative in concave mirror.