The far point of a myopic person is 80 cm in front of the eye. What is...
Far point of the defective eye, v = -80 cm
Object distance, u = -∞ (-infinity)
To find :
Nature and power of the corrective lens.
Solution :
1/v - 1/u = 1/f
1/f = 1/(-80) - 1/(-∞)
1/f = - 1/80 + 0 [Since, 1/-∞ = 0]
1/f = - 1/80
f = -80 cm
Therefore, the corrective lens should be of the focal length 80 cm.
Power, P = 1 / focal length
As focal length is in centimetres, 1 m = 100 cm.
P = 100 / -80
P = -1.25 D
Therefore, the corrective lens is diverging or concave lens of power -1.5 D.
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The far point of a myopic person is 80 cm in front of the eye. What is...
The corrective lens is diverging or concave lens of power -1.25 D.
The far point of a myopic person is 80 cm in front of the eye. What is...
To correct myopia, a diverging lens is required. Let's understand this in detail.
1. Understanding Myopia:
Myopia, also known as nearsightedness, is a refractive error where the individual can see nearby objects clearly but has difficulty focusing on distant objects. In myopia, the image is formed in front of the retina instead of directly on it.
2. Far Point:
The far point is the maximum distance at which a myopic person can see objects clearly without any optical aid. In this case, the far point is given as 80 cm in front of the eye.
3. Corrective Lens:
To correct myopia, a diverging lens is used. A diverging lens is thinner in the center and thicker at the edges. It disperses light rays and causes them to diverge, which helps move the image back to the retina.
4. Lens Power:
The power of a lens is measured in diopters (D). It indicates the ability of the lens to converge or diverge light. A positive power indicates a converging lens, and a negative power indicates a diverging lens.
5. Determining the Lens Power:
To determine the lens power required to correct myopia, we use the formula:
Lens Power (P) = 1 / Focal Length (f)
The focal length is the distance from the lens to the point where parallel light rays converge or diverge.
In this case, the far point is 80 cm in front of the eye. Since the far point is before the retina, a diverging lens is required to move it back to the retina. So, the lens power should be negative.
Using the formula, we calculate:
P = 1 / (-0.8) = -1.25 D
Therefore, the nature and power of the lens required to correct the myopic person's far point of 80 cm in front of the eye is a diverging lens of power -1.25 D.
Hence, the correct answer is option C - a diverging lens of power -1.25 D.
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