Question

(a) What is short-sightedness? State the two causes of short-sightedness (or myopia). With the help of ray diagrams, show
(i) the eye-defect short-sightedness.
(ii) correction of short-sightedness by using a lens.
(b) A person having short-sight cannot see objects clearly beyond a distance of 1.5 m. What would be the nature and power of the corrective lens to restore proper vision?

Answer 1

Answer:

the eye-defect short-sightedness

Answer 2

Explanation:

(a)

• Near-sightedness, or short-sightedness, is an eye deficiency which prevents a person from seeing distant objects clearly but has an usual close-sightedness. Short-sightedness occurs due to the eye lens high intersecting power (pictures are created in front of the retina), and because the eyeball is much long (pictures are created in front of the retina).
• In the diagram, the short-sightedness and how concave lenses can correct the defect by diverging the rays of light entering the eye to form clear pictures of objects on the retina is shown.

(b) A person with a short-sightedness can correct the defect by wearing concave lens fitting spectacles. To find the concave lens power we must first measure its focal length.

Assuming that the short-sighted person's distance is 1.5 m from the eye (the person can see the object being held at infinity if the object's picture is created at the person's own distance of 1.5 m from the eye).

u = ∞  (The difference between objects)

v = -1.5 m  (Far end of the eye fault in front of the lens)

f = ? (focal length)  

The focal length can be determined using the formula for lens

$\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$

Replacing the values in the formula, we obtain

$\frac{1}{-1.5} -\ \frac{1}{\infty} = \frac{1}{f}$

f = -1.5 m

Since, 1/∞ =0  

Now that we know the concave lens  focal length, it can calculate its power.

Power  (f in metres)

∴ P = - $\frac{1}{f}$   = - 0.667 Dioptres ≈ - 0.67 Dioptres

Consequently, the concave lens power required to fix the defect is -0.67 D.

You can get all the answers of Chapter 6 in the link below:    

https://brainly.in/question/14963310

   

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