Question

Resolution power of a compound microscope is -
(a)100㎛
(b)10㎛
(c)1㎛
(d)0.25㎛

Answer 1

Hint: The resolution power of a microscope is the ability of the instrument to form two separate images of the two objects placed very close to each other. A compound microscope is one of the simplest forms of optical microscopes.

Complete answer:
- The resolution power of a microscope is its ability to form two separate images of two objects placed very close to each other.
- Optical microscopes are instruments used to magnify very small objects that are not visible to the naked eye using glass lenses.
-In Compound microscopes, two lenses are used to magnify objects. The two lenses are the ocular lens found in the eyepiece and the objective lens found in the revolving nosepiece. It can resolve objects down to about 0.2㎛. The microscope has a magnifying power of $2000\times$.

Additional Information:
- The resolving power of a microscope is mathematically calculated as follows.
The minimum separation between two objects that are to be resolved by a microscope is given by the formula
${ d }_{ min }\quad =\quad \dfrac { 1.22\lambda }{ 2n\sin { \theta } }$
The resolving power of a microscope is the reciprocal of the minimum distance.
Therefore, it can be denoted as
Resolving Power (R.P.) = $\dfrac { 1 }{ { d }_{ min } }$ = $\quad \dfrac { 1.22\lambda }{ 2n\sin { \theta } }$
$\therefore \quad R.P.\quad \propto \quad \dfrac { n\sin { \theta } }{ \lambda }$
Where, n is the refractive index, and lambda is the wavelength.
From this expression, we deduce that R.P. is directly proportional to the refractive index and sinθ, inversely proportional to the wavelength, and independent of the focal length of the lens.

So, the correct answer is ‘(d)0.25㎛’.

Note: - The numerical aperture of the objective lens determines the resolving power as well as the light-collecting capability of the microscope.
- The resolution also increases by using the light of a shorter wavelength.