1. What is light?
Ans: Light is a form of energy that gives the sensation of sight.
2. What is convex mirror?
Ans: If the reflecting surface is curved outwards and the inside is silvered, it is called convex mirror.
OR
Convex mirror is a spherical mirror whose outer surface is reflecting and inner surface is silvered.
3. What is concave mirror?
Ans: Concave mirror is a spherical mirror whose inner surface is reflecting and outer surface is silvered.
4. What is reflected ray?
Ans: The ray of light which is reflected back on the same medium after striking on the surface is called reflected ray.
5. What is angle of incidence?
Ans: The angle between the incident ray and normal is called angle of incidence.
6. What is real image?
Ans: An image that can be obtained on a screen is called real image.
7. What is virtual image?
Ans: An image that cannot be obtained on a screen is called virtual image.
8. What is focal length?
Ans: The distance between focus and pole of mirror is called focal length.
9. What is reflection of light?
Ans: The process of returning of light into the same medium is called reflection of light.
10. What is denser medium?
Ans: The medium in which the velocity of light is less is called denser medium.
11. What is beam of light?
Ans: A collection of rays of light is called beam of light.
12. What are the sources of light?
Ans: The bodies which give light are called sources of light.
13. What is regular reflection?
Ans: The reflection in which the reflected rays are parallel to eachother when a parallel beam of light is incident on a smooth surface is called regular reflection.
OR
The reflection of light in regular surface is called regular reflection.
14. What is irregular reflection?
Ans: The reflection in which the rays are reflected in different directions from the surface when a parallel beam of light is incident on a rough surface is called irregular reflection.
15. What is incident ray?
Ans: The ray of light coming from the source which is incident on a surface is called incident ray.
16. What is a plane mirror?
Ans: The mirror whose reflecting surface is flat is called plane mirror.
17. What is refraction of light?
Ans: The bending of the light as it passes from one optical medium to another is called refraction of light.
18. What is mirror?
Ans: Mirror is a surface which reflects a large fraction of incident light and forms the image of an object.
19. What is angle of reflection?
Ans: The angle between the reflected ray and the normal is called angle of reflection.
20. What is optics?
Ans: The branch of physics that deals with the study of light is called optics.
21. Why does refraction occur? Write any two laws of refraction of light.
Ans: Light travels with different speeds in different media. When a ray of light travels from rarer to a denser medium, its speed decreases. Similarly, when the light travels from denser to rarer medium, its speed increase. Such a sudden change in the speed of light as it passes from one medium to another medium causes it to be bent from its original path. Due to this reason, light undergoes refraction.
The refraction of light obeys the following two laws:
• The incident ray, the refracted ray and normal, to the surface of separation at the point of incidence, all lie in the same plane.
• The ratio of sine of the angle of incidence and sine of the angle of refractive is always constant for a given pair of media.
Mathematically,
sini/sinr = (a constant)
22. What is the convex mirror? Write any two uses of convex mirror.
Ans: If the reflecting surface is curved outward and the inside is silvered, it is called a convex mirror.
Uses of convex mirror are as following:
• Convex mirrors are used in street lights to scatter light in the wider regions.
• Convex mirrors are widely used in automobiles to have a clear view of the traffic behind.
23. What is plane mirror? Convex mirror is called a diverging mirror. Why?
Ans: A plane mirror is a type of mirror whose reflecting surface is flat.
Convex mirror is also known as a diverging mirror because it diverges that the light rays incident on its reflecting surface.
24. Write two difference between real and virtual image.
25. What is the center of curvature? Write any two uses of concave mirror?
Ans: The centre of the sphere, of which a mirror forms a part, is called centre of curvature. It is generally denoted by C.
Uses of concave mirror are as followings:
• Doctors use concave mirror to observe interior parts of our body such as ear, nose, mouth and throat.
• Torches, searchlight and headlight of car use concave mirrors to focus light.
26. Write two differences between denser and rarer medium.
27. What is focal length? Concave mirror is called a converging mirror, why?
Ans: The distance between focus and pole of mirror is called focal length. It is generally denoted by 'f'.
The concave mirror is also known as converging mirror because it converges the light rays falling on it.
28. What is virtual image? Draw a ray diagram formed by concave mirror when an object is placed at infinity.
Ans: Those images which can be seen only by looking into a mirror or lens but cannot be received on a screen are called virtual images.
When an object is at infinity, the parallel beam coming from it meets at the focus F of the concave mirror after reflection. The image formed is real, inverted and highly diminished.
Fig: Concave mirror, when object is placed at infinity
29. Concave mirror is used to make solar stove, why? Complete the following ray diagram.
Ans: As concave mirrors are converging type of mirrors these mirror will focus the infrared rays from son on a point. So, the stove will be heated easily and food will get more heated.
30. A pencil partially immersed in water seems bent? Why?
Ans: Pencil partially immersed in water seems bent due to the phenomenon of refraction. When light ray travels from denser to rarer medium it bends away from normal. Water is a denser medium and air is rarer medium. The light reaching our eye from the portion of the pencil appears to come from different direction, compared to the part above water because the ray of light arising from immersed portion of pencil travels from denser (water) to rarer (air) medium. That is why the pencil appears bent at the interface.