In: Physics
A microscope is used to examine a sample of bacteria that are
spread on glass. If the diameter of the objective is twice its
focal length and the sample is near the focal point of the
objective, determine the shortest distance between two bacteria
that can be resolved under the microscope in the terms of the
wavelength ? of the light source.
.
The shortest distance between two objects that can be resolved, when viewed with an optical instrument is known as resolution limit d of the instrument. For microscope it is given as,
Here, ? is the wavelength of the light used to illuminate the microscope
NA is numerical aperture for the objective lens and it is given as
Here, n is the refractive index of the medium in which objective lens is placed (For air n =1)
? is the angle of cone of the light coming from objective.
Given:
Diameter of the objective is twice the focal length,
Sample is near focal point
Solution:
From the figure above Numerical aperture can be given as,
For microscope resolution limit is given as,
Substituting the value of numerical aperture in above equation we have,
Thus, the shortest distance between two bacteria that can be resolved under the microscope in the terms of the wavelength ? of the light source is .