Light

Q1. Fill in the blanks.

                          i.        A person 1 m in front of a plane mirror seems to be 2 m from his image.

                         ii.        If you touch your left ear with right hand in front of a plane mirror it will be seen in the mirror that your right ear is touched with left hand.

                        iii.        The size of the pupil becomes large when you see in dim light.

                        iv.        Night birds have lesser cones than rods in their eyes.

                         v.        In the iris, there is a small opening called the pupil.

                        vi.        The impression of an image does not vanish immediately from the retina.  It persists there for about 1/16th of a second.

          vii.        If still images of a moving object are flashed on the eye at a rate faster than 16 per second, then the eye perceives this object as moving.

Q2. State True (T) or False (F).

                          i.        The moon is not an illuminated object. F

                         ii.        Interesting feature of a kaleidoscope is that you will never see the same pattern again. T

                        iii.        Sunlight, called white light, consists of eight colours. F

                        iv.        Visually challenged persons can read and write using Braille system. T

                         v.        Two mirrors inclined to each other give multiple images. T

                        vi.        Light is reflected from all surfaces. T

Q3. Name a device which works on the reflection of reflected light.

Ans. Periscope

Q4. Name the point inside the human eye where no vision is possible.

Ans. Blind spot

Q5. Name an eye disease caused by the deficiency of vitamin A in the diet.

Ans. Night blindness

 
Q6. What type of reflection of light takes place from a plane mirror?

Ans. Regular reflection

Q7. Which part of the eye converges light rays to form the image?

Ans. Eye lens

Q8. Where is the image of an object formed in human eye?

Ans. Retina

Q9. Which part of the eye carries images to the brain?

Ans. Optic nerve carries images to the brain.

Q10. How many mirrors are there in a periscope?

Ans. The periscope makes use of two plane mirrors.

Q11. Name an instrument or toy which works by producing multiple reflections from three plane mirrors to form beautiful patterns.

Ans. Kaleidoscope

Q12. Angle of incidence is equal to the angle of reflection
(a) Always (b) Sometimes (c) Under special conditions (d) Never

Ans. (a) Always

Q13. How many images of a candle will be seen when two mirrors are set parallel to each other and a candle is placed between them?

Ans. Infinite number of images of the candle will be formed.

Q14. What type of reflection of light takes place from a rough surface?

Ans. The diffuse reflection of light takes place from a rough surface.

Q15. What type of reflection of light takes place from a smooth surface?

Ans. Regular reflection of light takes place from a smooth surface.

Q16. Which type of reflection of light leads to the formation of images?

Ans. Images are formed by regular reflection.

 
Q17. What is an 'incident ray'?

Ans. The light ray, which strikes any surface, is called the incident ray.

Q18. What kind of lens (convex or concave) is there in our eyes?

Ans. The human eye has convex lens.

Q19. What are the main parts of the human eye?

Ans. Important parts of the eye are cornea, iris, pupil, lens, retina and optic nerve.

Q20. What is angle of incidence?

Ans. The angle between the normal and incident ray is called the angle of incidence (∠i).