Question

an object kept at a distance of 20cm in front of a concave mirror the focal length of a mirror is 30cm find the magn​

Answer 1

Answer:

Magnification = 0.3

Explanation:

Given :

u = - 20 cm

f = - 30 cm

We know that by Mirror formula ,

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

$\frac{1}{v} = \frac{ - 1}{30} + \frac{ 1 }{20}$

$\frac{1}{v} = \frac{ - 20 + 30}{600} = \frac{10}{600} = \frac{1}{6}$

v =

v = 6 cm

Now ,

$\large \color{purple} \boxed{\mathbf{Magnification = - v / u}}$

=> m = -6 / -20 = 3/10 = 0.3

Answer 2

Given:

$\sf{f=-30cm}$

$\sf{u=-20cm}$

$\sf{Mirror= Concave \:Mirror}$

Solution:

$\sf{{\dfrac{1}{f}}={\dfrac{1}{v}}+{\dfrac{1}{u}}}$

$\sf{{\dfrac{1}{v}}=-{\dfrac{1}{30}}+{\dfrac{1}{20}}}$

$\sf{{\dfrac{1}{v}}={\dfrac{-2+3}{60}}}$

$\sf{{\dfrac{1}{v}}={\dfrac{1}{60}}}$

$\sf{v=60cm}$

$\bold{Magnification:}$

$\sf{Magnification=}{\dfrac{-v}{u}}$

$\sf{Magnification=}{\dfrac{-60}{-20}}$

$\sf{Magnification=3}$

Thus, the image formed will be 3 times the height of object and the image will form behind the mirror. The image formed will be virtual and erect.