Q21. What do you mean by ‘point of incidence’?
Ans. The point of incidence is the point where the
incident ray strikes the mirror.
Q22. How we see the moon?
Ans. Moon receives light from the sun and reflects it.
That’s how we see the moon.
Q23. What are the two types of reflection of light?
The two types of reflection of light are Regular reflection of light and
Diffused reflection of light.
Q24. What is a ' reflected
Ans. The ray that comes back from the surface after
reflection is known as the reflected ray.
Q25. What is angle of reflection?
The angle between the normal and the reflected ray is known as the angle of reflection
Q26. What are the uses of periscope?
Ans. Periscopes are used in submarines, tanks and also
by soldiers in bunkers to see things outside.
Q27. Write the uses of kaleidoscope.
Ans. Designers of wallpapers and fabrics and artists
use kaleidoscopes to get ideas for new patterns.
Q28. What are luminous objects? Give some examples.
Ans. The objects which emit their own light are known
as luminous objects. Example: sun, fire, flame of a candle and an electric
Q29. What are illuminated objects? Give one example.
Ans. The objects which shine in the light of other
objects are called illuminated objects. Example: moon.
Q30. Why cannot we see a book which is placed behind a wooden
Ans. Wooden screen are opaque object that does not
allow light to pass through it. Thus we are not able to see through it.
Q31. What is blind spot in the eye?
Ans. At the junction of the optic nerve and the
retina, there are no sensory cells, so no vision is possible at that spot. This
is called the blind spot.
Q32. What type of image is formed by a plane mirror?
Ans. The image formed by a plane mirror is always
virtual, upright, and of the same shape and size as the object it is
Q33. What is lateral inversion?
In an image formed by a mirror the left of the object appears on the right and
the right appears on the left. This is known as lateral inversion.
Q34. What is the most comfortable distance at which one can read
with a normal eye?
Ans. The most comfortable distance at which one can
read with a normal eye is about 25 cm.
Q35. What is meant by dispersion of light'? Name a natural
phenomenon showing dispersion.
Ans. Splitting of light into its colours is known as
dispersion of light. Rainbow is a natural phenomenon showing dispersion.
Q36. A ray of light is incident on a plane mirror at an angle of
40°. What is the angle of reflection?
Ans. The angle of reflection will be 40 degree. This
is by the law of reflection that angle of incidence is equal to the angle of
Q37. Gurmit wanted to perform Activity 16.8 using a laser torch.
Her teacher advised her not to do so. Can you explain the basis of the teachers
Ans. Laser light is harmful for the human eye because
it can injure the retina. Hence, it is advisable not to look at a laser beam
Q38. Which part of the eye gives it its distinctive color?
Ans. The iris is the part of that eye which gives it
its distinctive colour. When we say that a person has green eyes, we refer
actually to the colour of the iris.