A person wears glasses of power -2.5 D . What is the far point of the person without the glasses ?

Question

A person wears glasses of power -2.5 D . What is the far point of the person without the glasses ? (A) 40 cm (B) 20 cm (C) 15.3 cm (D) 66.6 cm

Tardigrade Admin · Accepted Answer

P =-2.5 D i.e. concave lens, the person is nearsighted, f =(100/-2.5)=-40 (1/-( F . P .))-(1/ text-( distance ))=(1/ f ) (1/-( F . P .))-(1/∞)=(1/-40) ⇒ F . P .=40 cm

Q. A person wears glasses of power $- 2.5 D$ . What is the far point of the person without the glasses ?

40 cm

20 cm

15.3 cm

66.6 cm

$P = - 2.5 D$ i.e. concave lens, the person is nearsighted,
$f = \frac{100}{- 2.5} = - 40$
$\frac{1}{- ( F . P . )} - \frac{1}{-( distance )} = \frac{1}{f}$
$\frac{1}{- ( F . P . )} - \frac{1}{\infty} = \frac{1}{- 40}$
$\Rightarrow F . P . = 40 c m$

Q. A person wears glasses of power −2.5D . What is the far point of the person without the glasses ?