1. Resolving Power 1 1 1

2. Not resolved
Well resolved

3. Just resolved

4. Chromatic Resolving Power
The ability of the spectroscope or the interferometer to separate the components of multiplets is known as chromatic resolving power (CRP).
In a two beam interferometer, like Michelson interferometer and Young’s double slit set-up, the bright fringes are as broad as the dark fringes. The fringes are not sharp.
For good resolution, the bright fringes must be as sharp as possible.

5. Michelson
fringes
Fabry-Perot
fringes 5

6. Fabry-Perot interferometer
Doublet separation in
Fabry-Perot interferometer 6

7. Resolved wavelengths
s: separation
w: width 7

8. Unresolved wavelengths8

9. Barely resolved 9

10. Chromatic resolving power of Fabry Perot interferometer
- Where, λ is the minimum wavelength interval of a doublet that the instrument is capable of barely resolving.
- The criterion for bare resolution is called the Rayleigh criterion.
- The smaller the value of λ, the higher is the resolving power of the instrument.
Barely resolved
Using: 2d cos θm= mλ ; ( Fabry-Perot - bright fringe in transmission ) 10

11. Telescope
R.P. = 1.22 λ / D
D= Diameter of the telescope objective

12. Single slit – Two point sources
R.P. = λ / b

13. Circular aperture

14. Chromatic resolving power of a grating
= m N