near point of an eye is 50 cm and far point is 4 m . Which lenses should be use t read as well as see movie clearly?
To determine the lenses that should be used to read and see a movie clearly, we need to understand the concept of near point and far point, as well as the concept of lenses.
The near point is the closest distance at which the eye can focus on an object comfortably. In this case, the near point is given as 50 cm (or 0.5 m). The far point is the farthest distance at which a person can see a distant object clearly without any strain on the eyes. In this case, the far point is given as 4 m.
Now, let's discuss the lenses that can be used to correct nearsightedness (myopia) for reading and watching a movie. Nearsightedness occurs when the distance vision is blurry, and objects in the distance appear blurred while nearby objects can be seen clearly.
To correct myopia, concave lenses (also known as diverging lenses) are used. Concave lenses are thinner in the middle and thicker at the edges. They diverge the incoming light, allowing the image to be focused further back onto the retina.
To determine the power of the lenses needed, we can use the formula:
Power (P) = 1 / focal length (f)
where the focal length is the distance at which the lens focuses the light to form an image.
For reading, the near point is given as 50 cm. Since the near point is the closest distance, the focal length of the lens needed can be calculated as:
f = 1 / 0.5 = 2 diopters (D)
For watching a movie, the far point is given as 4 m. As the far point is the farthest distance, we need to find the focal length accordingly:
f = 1 / 4 = 0.25 diopters (D)
Therefore, to read clearly, you would need a concave lens with a power of -2 D, and to see a movie clearly, you would need a concave lens with a power of -0.25 D. These lenses will help correct your nearsightedness and allow you to have clear vision at the desired distances. It is important to consult an optometrist or ophthalmologist to get your eyes accurately tested and determine the specific lens prescription suitable for your vision.