Question

A convex lens has a focal length of $15cm$. At what distance from the lens should the object be placed so that it forms on its other side real inverted image $30cm$ away from the lens? What would be the size of image formed if the object is $5cm$ high?

• A. 5 cm
• B. 10 cm
• C. 15 cm
• D. 12 cm

Answer 1

Answer: (A)

5 cm

Given data,

$f=15cm$

$v=30cm$

$h=-5cm$

$u=?$

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

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

$=\frac{1}{30}-\frac{1}{15}$

$=\frac{1-2}{30}$

$=\frac{-1}{30}$

$\Rightarrow u=-30cm$

Also we know that,

$m=\frac{+v}{u}=\frac{h^{\prime }}{h}$

$\Rightarrow \frac{-30}{30}=\frac{h}{-5}$

$\Rightarrow h=+5$

$\therefore objectheight=5cm$