What is the resolving power for light microscopes, and what is it for electron microscopes?
The resolving power of a microscope refers to its ability to distinguish and separate two closely spaced objects as distinct entities. In other words, it quantifies how much detail can be observed by the microscope.
For light microscopes, the resolving power is approximately limited by the wavelength of light used. The maximum resolving power of a light microscope is determined by a formula known as the Abbe's formula:
Resolving power (in micrometers) = 0.61 x (wavelength of light used in micrometers) / Numerical Aperture
The numerical aperture is a characteristic of the microscope objective and it depends on the design and properties of the lens. The value of the numerical aperture ranges typically from 0.1 to 1.4, with higher values resulting in better resolution.
On the other hand, electron microscopes use electrons instead of light to image specimens. Due to the shorter wavelength of electrons compared to visible light, electron microscopes have significantly higher resolving power. The resolving power of electron microscopes can be calculated using a different formula called the Scherzer equation:
Resolving power (in angstroms) = 0.143 x (wavelength of electrons in angstroms) / Numerical Aperture
For electron microscopes, the numerical aperture is determined based on the configuration and properties of the electromagnetic lenses used within the microscope. The numerical aperture values for electron microscopes are typically between 0.1 to 0.5, resulting in much higher resolving power compared to light microscopes.
In summary, light microscopes have relatively lower resolving power compared to electron microscopes due to the longer wavelength of visible light.