Question

The focal length of a convex lens is given to be 17 cm. It's magnification is -2.5. (a) What is the distance of the object and image from the lens? (b) What is the image height if the object is 15 cm? (c) Draw a ray diagram for this situation, label completely.

Answer 1

Magnification is defined as

$m = \frac{v}{u}$

W = : -2.50

Using the lens formula

$\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$

So,

$-\frac{1}{2.5u} - \frac{1}{u} = \frac{1}{17}$

1.4 u 17

and

$v = 2.5 \times 23.8$

Part b)

magnification can also be defined as

$m = \frac{I}{O}$

$I = 2.5 \times 15$

Part C)

Image 1 o object f t -23.8 59.5