Topic outline

    • Light

      Q39. What happens to the size of the pupil of our eye in bright light?

      Ans. In bright light the size of the pupil of our eye becomes small to reduce the amount of light going inside the eye. The size of the pupil is controlled by the iris.


      Q40. How can you show that white light consists of seven colors?

      Ans. White light consists of seven colors can be shown by passing the light through a prism. The sunlight passes through the prism and splits into a band of 7 colors.


      Q41. What makes things visible?

      Ans. Eyes alone cannot see any object. It is only when light from an object enters our eyes that we see the object. The light may have been emitted by the object, or may have been reflected by it.

      Q42. What is 'normal' in the reflection of light from a plane mirror?

      Ans. A line drawn making an angle of 90º to the line representing the mirror at the point where the incident ray strikes the mirror is known as the normal to the reflecting surface at that point.


      Q43. What is the name of transparent front part of an eye?

      Ans. The eye has a roughly spherical shape. Outer coat of the eye is white. It is tough so that it can protect the interior of the eye from accidents. Its transparent front part is called cornea.


      Q44. Name some food items which are rich in vitamin A.

      Ans. Raw carrots, broccoli and green vegetables (such as spinach) and cod liver oil are rich in vitamin A. Eggs, milk, curd, cheese, butter and fruits such as papaya and mango are also rich in vitamin A.

      Q45. Why too little or too much light is bad for our eyes?

      Ans. Too little or too much light is bad for eyes. Insufficient light causes eyestrain and headaches. Too much light, like that of the sun, a powerful lamp or a laser torch can injure the retina.


      Q46. A book lying on a table in a room can be seen from all the parts of the room. Give reason?

      Ans. A book lying on a table in a room can be seen from all the parts of the room because the light is reflected by the book and it reaches our eye at any part of the room.


      Q47. What should we do if something like a dust particle or an insect gets into our eye?

      Ans. If something like a dust particle or an insect gets into our eye, we should never rub the eye instead wash the eye with clean water. If there is no improvement, we should consult a doctor immediately.

      Q48. How a hair dresser makes us see hair at the back of our head after the hair cut is complete?

      Ans. Hair dresser uses the phenomena of multiple reflections to provide view of the back of our head. After our hair cut is complete, he places a mirror at our back to show us how the hair has been cut.


      Q49. State the laws of reflection.

      Ans. Two laws of reflection are

      (i) The angle of incidence is equal to the angle of reflection.

      (ii) Incident ray, reflected ray and the normal drawn at the point of incidence to the reflecting surface, lie in the same plane.


      Q50. How do we see a moving picture or a movie?

      Ans. The movies that we see are actually a number of separate pictures in proper sequence. They are made to move across the eye usually at the rate of 24 pictures per second (faster than 16 per second). So, we see a moving picture.

      Q51. What are rods and cones in the retina of an eye?

      Ans. There are two kinds of light sensitive cells on the retina.

      (i) cones, which are sensitive to bright light and

      (ii) rods, which are sensitive to dim light.

      Besides, cones sense colour.


      Q52. Boojho stands at A just on the side of a plane mirror as shown in figure. Can he see himself in the mirror? Also can he see the image of objects situated at P, Q and R?

       From NCERT

      Ans. He cannot see his image himself. He can see only the image of P but not Q and R.


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