Question

2 cm tall object is placed at a distance of 32 cm from a comcave mirror.the image is real and inverted and 3 cm in size find the focal lenght

Answer 1

Answer:

given,

length of object (l)=2 cm

length of image (l')=3 cm

we know,

magnification,m=l'/l= 3/2

now,

distance of object from mirror (u)=32 cm

we know,

$m = - \frac{v}{u} \\ > \frac{3}{2} = - \frac{v}{32} \\ > v= - 48$

now,

$\frac{1}{f} = \frac{1}{u} + \frac{1}{v} = \frac{1}{32} + \frac{1}{48} = \frac{3 + 2}{96} = \frac{5}{96} \\ > f = \frac{96}{5} = 19.2$

so the required focal length=19.2 cm

Answer 2

Hope this may help you