Question

Two refracting media are separated by a spherical interface as shown in the figure. PP' is the principle axis. ${\mu }_1$ and ${\mu }_2$ are the refractive indices of the medium of incidence and medium of refraction respectively. Then:

• A. If ${\mu }_2>{\mu }_1$ then there cannot be a real image of real object.
• B. If ${\mu }_2>{\mu }_1$ , then there cannot be a real image of virtual object.
• C. If ${\mu }_1>{\mu }_2$ , then there cannot be a virtual image of virtual object.
• D. If ${\mu }_1>{\mu }_2$ then there cannot be a real image of real object.

Answer 1

Answer: (A), (C)

If ${\mu }_2>{\mu }_1$ then there cannot be a real image of real object.
If ${\mu }_1>{\mu }_2$ , then there cannot be a virtual image of virtual object.

We use the lens formula involving 2 refractive media,

$\frac{{\mu }_2}{V}-\frac{{\mu }_1}{u}=\frac{{\mu }_2-{\mu }_1}{R}$

Now, R is always negative.
Case 1 : ${\mu }_2>{\mu }_1$ and U < 0 (Real object)
V cannot be negative.
Thus, the image can never be real.
Case 2 : ${\mu }_2<{\mu }_1$ and U > 0 (Virtual object)
V can never be +ve, thereby a virtual image can never form