A person uses glasses of power – 2.5 D to correct his vision, his far point without using glasses isOnly one correct answerA.45 cmB.35 cmC.40 cmD.50 cm

The power of a lens is given by the formula:

P = 1/f

where P is the power of the lens and f is the focal length. The power is given in diopters (D) and the focal length is given in meters.

In this case, the power of the glasses is -2.5 D. The negative sign indicates that these are diverging lenses, which are used to correct nearsightedness (myopia).

We can rearrange the formula to solve for the focal length:

f = 1/P

Substituting the given power:

f = 1/(-2.5 D) = -0.4 m

The negative sign indicates that the focal point is virtual and located on the same side of the lens as the object. However, in practice, we often take the absolute value when referring to the distance of the far point, so the far point is 0.4 m or 40 cm from the eye.

Therefore, the correct answer is C. 40 cm.