Optics Question 443
Question: A point object is placed at a distance of 10 cm and its real image is formed at a distance of 20 cm from a concave mirror. If the object is moved by 0.1 cm towards the mirror, the image will shift by about
Options:
A) 0.4 cm away from the mirror
B) 0.4 cm towards the mirror
C) 0.8 cm away from the mirror
D) 0.8 cm towards the mirror
Show Answer
Answer:
Correct Answer: A
Solution:
[a] Mirror formula $ \frac{1}{f}=\frac{1}{v}+\frac{1}{u}\Rightarrow \frac{1}{f}=\frac{1}{-20}+\frac{1}{(-10)}\Rightarrow f=\frac{20}{3}cm $
If object moves towards the mirror by 0.1 cm then. $ u=(10-0.1)=9.9cm. $
Hence again from mirror formula $ \frac{1}{-20/3}=\frac{1}{v’}+\frac{1}{-9.9}\Rightarrow b’=20.4 $ i.e., image shifts away from the mirror by 0.4 cm.
