Question

The power of a convex lense is 5D.At what distance object should be placed from the lense so that, 2 times larger image is formed.

Answer 1

Answer on Question#39498, Physics, Optics

The power of a convex lens is 5D. At what distance object should be placed from the lens so that, 2 times larger image is formed.

Solution:

The linear magnification of a thin lens is

$$M = \frac {f}{f - d _ {o}} = \frac {h _ {i}}{h _ {o}} = 2$$

where $f$ is the focal length and $d_{0}$ is the distance from the lens to the object.

$$d _ {o} = \frac {f (M - 1)}{M}$$

The power of a lens is 1/focal length (measured in meters):

$$P = \frac {1}{f} = 5 \mathrm {D}$$

Thus,

$$f = \frac {1}{D} = \frac {1}{5} = 0. 2 \mathrm {m}$$ $$d _ {o} = \frac {f (M - 1)}{M} = \frac {0 . 2 (2 - 1)}{2} = 0. 1 \mathrm {m}$$

Answer. $0.1\mathrm{m}$