Q135 / 160 · AP EAMCET 2020 (22 Sep Shift 1) · Physics
A travelling micros dot marked on a pi slab $(\mu=1.5)$ of thic the ink dot. The tra be moved in focus.
- A$0.04 \mathrm{~m}$, downwards
- Correct answerB$0.04 \mathrm{~m}$, upwards
- C$0.06 \mathrm{~m}$, downwards
- D$0.06 \mathrm{~m}$, upwards
Solution
We know that,
Refractive index, $\mu=\frac{\text { Real depth }}{\text { Apparent depth }}$
Here, $\mu=1.5$ and real depth $=$ thickness of glass $\mathrm{slab}=0.12 \mathrm{~m}$
$\therefore \quad \mu=\frac{012}{\text { Apparent depth }}$
Apparent depth $=\frac{0.12}{1.5}=0.08 \mathrm{~m}$
Hence, image appears to be raised by
$$
\frac{0.08}{2} \mathrm{~m}=0.04 \mathrm{~m}
$$
Hence, travelling microscope must be moved upward by $0.04 \mathrm{~m}$.
Hence, the correct answer is option: 'B'.