Notifications
Clear all
Light Reflection and Refraction
1
Posts
2
Users
0
Likes
687
Views
0
11/08/2021 7:29 pm
Topic starter
How far should an object be placed from the pole of a converging mirror of focal length 20 cm to form a real image of the size exactly 1/4 th the size of the object?
1 Answer
0
11/08/2021 7:35 pm
f = -20 cm, m = -\(\frac{1}{4}\)(real image)
We know that
m = -\(\frac{v}{u}\)
\(-\frac{1}{4}\) = -\(\frac{v}{u}\)
u = 4v
So,
\(\frac{1}{v}\) + \(\frac{1}{u}\) = \(\frac{1}{f}\)
\(\frac{1}{v}\) + \(\frac{1}{4v}\) = \(\frac{1}{-20}\)
\(\frac{5}{4v}\) = -\(\frac{1}{20}\)
v = -\(\frac{100}{4}\) = -25 cm
∴ u = 4v
u = 4 x (-25)
= -100 cm
The object should be placed 100 cm to the left of the mirror.