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A student wishes to study the cell structure under a light microscope having 10X eyepiece and 45X objective. He should illuminate the object by which one of the following colours of light so as to get the best possible resolution -
A
Red
B
Green
C
Yellow
D
Blue
Detailed Solution
The resolving power of a microscope is its ability to show two closely placed points as separate.
The limit of resolution is $d = \dfrac{0.61\lambda}{n\sin\theta}$ (Abbe's formula), so it is directly proportional to the wavelength $\lambda$ of the light used.
The shorter the wavelength, the smaller the distance that can be resolved, i.e. the better the resolution.
Among the given colours, blue light has the shortest wavelength (about 450 nm), compared with green (about 530 nm), yellow (about 580 nm) and red (about 700 nm).
The magnification of the eyepiece and objective does not change this.
So the object should be illuminated with blue light for the best resolution.
The limit of resolution is $d = \dfrac{0.61\lambda}{n\sin\theta}$ (Abbe's formula), so it is directly proportional to the wavelength $\lambda$ of the light used.
The shorter the wavelength, the smaller the distance that can be resolved, i.e. the better the resolution.
Among the given colours, blue light has the shortest wavelength (about 450 nm), compared with green (about 530 nm), yellow (about 580 nm) and red (about 700 nm).
The magnification of the eyepiece and objective does not change this.
So the object should be illuminated with blue light for the best resolution.