A farsighted man has a near point of 50 cm. What power lens should he use as a magnifier to see clearly at a distance of 15cm without wearing his glasses?
11.5
To find the power of lens the farsighted man should use as a magnifier to see clearly at a distance of 15 cm, you can use the lens formula:
1/f = 1/v - 1/u
Where:
- f is the focal length of the lens
- v is the image distance (distance of clear vision)
- u is the object distance (distance between the lens and the object)
In this case, the object distance (u) is 50 cm (near point of the farsighted man) and the image distance (v) is 15 cm (desired distance of clear vision). We can assume that the lens is being used as a magnifier, so we can consider the object distance as negative (-50 cm).
1/f = 1/v - 1/u
1/f = 1/15 - 1/(-50)
Simplifying this equation will give you the focal length (f) of the lens. The power (P) of a lens is given by the formula:
P = 1/f
Therefore, once you find the focal length (f), the corresponding power (P) of the lens will be the reciprocal of the focal length.
Note: The unit used for focal length and power of lens is diopters (D).
Using the assumed units, you can perform the calculation to find the power of the lens.