Question

calculate the image distance for an object of height 12mm from a concave lens of focal lenght 0.30m and state the nature and size of the image.

Answer 1

object distance = u = -0.2m = -20cm

focal length = f = -0.3m = -30cm

image distance = v

\frac{1}{v} - \frac{1}{u} = \frac{1}{f} \\ \\ \frac{1}{v} - \frac{1}{-20} = \frac{1}{-30} \\ \\ \frac{1}{v} = \frac{1}{-30} + \frac{1}{-20} = \frac{-3-2}{60} = \frac{-5}{60} \\ \\ v=- \frac{60}{5} =-12cm

m= \frac{v}{u} = \frac{-12}{-20}= \frac{3}{5} \\ \\ m= \frac{h'}{h} \\ \\ \frac{3}{5} = \frac{h'}{12mm} \\ \\ h'= \frac{12*3}{5}=7.2mm,\ erect,\ virtual