Human Eye and Colourful World Questions

5. HUMAN EYE AND COLOURFUL WORLD

1/2 Mark Questions

1. Which lens is used to correct the ‘Myopia’?

Ans: Bi-concave lens

2. Which lens is used to correct the ‘Hypermetropia’?

Ans: Bi-convex lens

3. What is the value of least distance of distinct vision ?

Ans: 25 cm

4. What is the angle of vision for a healthy human ?

Ans: 60o

5. If power of lens is 2D, then what is the focal length of that lens ?

Ans: 50 cm

6. Some times a person may suffer from both myopia and hypermetropia with aging. Then which lens

 he need to use ?

Ans: bi-focal lens

7. What is the value of maximum focal length of the eye lens ?

Ans: 2.5 cm

8. What is the value of minimum focal length of the eye lens ?

Ans: 2.27 cm

9. What is the distance between the eye lens and retina ?

Ans: 2.5 cm

10. What is the unit of power of lens ?

Ans: Dioptre (D)

11. Does eye lens form a real image or virtual image ?

Ans: Real image

12. What happens if the focal length of eye lens is beyond the range of 2.5 cm to 2.27 cm ?

Ans: The vision becomes blurred due to accommodation defects of the eye lens.

13. What happens when the eye has a minimum focal length less than 2.5 cm ?

Ans: The person suffering with myopia.

14. What happens when the eye has a minimum focal length greater than 2.27 cm ?

Ans: The person suffering with hypermetropia.

15. What is the least distance of distinct vision At a young age (below 10 years) ?

Ans: 7 to 8 cm.

16. What is the least distance of distinct vision in old age ?

Ans: about 1 to 2 m or even more.

17. What is the image distance in the eye ?

Ans: 2.5 cm

18. Which lens is used to correct the presbyopia ?

Ans: bi-focal lenses 

1 Mark Questions

1. Define ‘Least distance of distinct vision’.

Ans: To see an object comfortably and distinctly, it must be at a distance about 25cm. from our eyes. This distance is called ‘least distance of distinct vision’.

2. Define ‘angle of vision’.

Ans: 1. The maximum angle, at which we are able to see the whole object is called angle of vision.

2. The angle of vision for a healthy human being is about 60 degrees.

3. What is meant by a Presbyopia?

Ans: Presbyopia is a vision defect indicating that the power of accommodation of the eye usually decreases with ageing.

4. Define power of lens.

Ans: The reciprocal of focal length is called power of lens.

Power of lens P =1/f in metres 100/f in cm. The unit of power is dioptre (D).

5. What is the cause of presbyopia?

Ans: Presbyopia is a vision defect when the ability of accommodation of the eye decreases with aging.

6. Define ‘far point’.

Ans: The point of maximum distance at which the eye lens can form an image on the retina is called ‘far point’.

7. Define ‘near point’.

Ans: The point of minimum distance at which the eye lens can form an image on the retina is called near point.

8. What are the maximum and minimum focal lengths of the eye lens.

Ans: 1. Maximum focal length of the eye lens is 2.5 cm

 2. Minimum focal length of the eye lens is 2.27 cm.

9. What is the relation between power and focal length of the lens?

Ans:Power of lens P =1/f in metres 100/f in cm.

10. Does eye lens form a real image or virtual image?

Ans: The eye-lens forms a real and inverted image of an object on the retina.

11. How does eye lens change its focal length? (OR)

 What is the role of ciliary muscles in the eye? Write the answer in one or two sentences only.

Ans: The ciliary muscle helps the eye lens to change its focal length by changing the radii of curvature of the eye lens.

12. What happens if the eye lens is not able to adjust its focal length? (OR)

 What happens if the focal length of eye lens is beyond the range of 2.5 cm to 2.27 cm?

Ans: The person cannot see an object clearly and comfortably. The vision becomes blurred due to accommodation defects of the eye lens.

13. How can we get same image distance for various positions of objects?

Ans: The eye lens change its focal length to get same image distance for various positions of object in front of the eye.

14. Define accommodation of lens.

Ans: The ability of eye-lens to change its focal length is called “accommodation of lens”.