1. Tardigrade
  2. Question
  3. Physics
  4. Two thin similar convex glass pieces are joined together front to front with its rear portion silvered such that a sharp image is formed 20 cm from the mirror. When the air between the glass pieces is replaced by water (mw=4 / 3), then the image formed from the mirror is at a distance of

Question Error Report

Thank you for reporting, we will resolve it shortly

Back to Question

Q. Two thin similar convex glass pieces are joined together front to front with its rear portion silvered such that a sharp image is formed $20\, cm$ from the mirror. When the air between the glass pieces is replaced by water $\left(m_{w}=4 / 3\right)$, then the image formed from the mirror is at a distance ofPhysics Question Image

Ray Optics and Optical Instruments

Solution:

Initially it is simply a concave mirror with $f=-20\, cm , R=40\, cm$
$\therefore $ Power of mirror $\left(P_{m}\right)=\frac{1}{8}$
$=\frac{1}{0.2}=5 \,D$
Focal length of lens $=\frac{R}{2(\mu-1)}$
$=\frac{40}{2 \times\left(\frac{4}{3}-1\right)} $
$=60\, cm$
Power of lens $=\frac{1}{0.5} $
$=\frac{100}{50} \,D $
$\therefore $ Equivalent power $=2 P_{L}+P_{m} $
$P=\frac{50}{6}$
Net focal length $=\frac{1}{P}$
$=\frac{6}{50} \times 100$
$=12\, cm$