Question

By considering the maximum resolution possible, estimate the minimum useful magnification of the optical microscope and the scanning electron microscope.

Answer 1

Optical microscopy is a imaging techniue to produce a magnified image of a sample using a set of lenses and visible light.

In Scanning electron microscope(SEM) images are produced by scanning the surface of a sample with a focused beam of high energy electon. since the smaller wavelength of electons, they can resolve finer details of the sample with much precision as compared to opticalmicroscopy.

The Resolution of an optical microscope is defined as the shortest distance between two points on a specimen that can still be distinguished by the observer or camera system as separate entities. it depends on the numerical aperture (area through which light enters into the lense system) of the objective lense.

Resolution of human eye = 200m

Resolution of Optical microscope = 0.2m

Resolution of SEM = 1nm

Useful magnification of a microscope is defined as the ratio of resolution of human eye to resolution of the microscoe.

hence, Useful magnification of an optical microscope = 200m/0.2m 1000x

          Useful magnification of SEM = 200m/1nm 200,000x

that is, a sample can be viewed 1000 times larger throgh an optical microscope and 20,0000 times larger through SEM.