Light

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?

Ans. The two types of reflection of light are Regular reflection of light and Diffused reflection of light.

Q24. What is a ' reflected ray'?

Ans. The ray that comes back from the surface after reflection is known as the reflected ray.

Q25. What is angle of reflection?

Ans. The angle between the normal and the reflected ray is known as the angle of reflection (∠r).

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 lamp.

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 screen?

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 reflecting.

Q33. What is lateral inversion?

Ans. 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 reflection.

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 advise?

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 directly.

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.