Mastering Physics: ± Resolution of an Electron Microscope

An electron microscope is using a -keV electron beam. An atom has a diameter of about meters.

Part A
What is the wavelength of electrons in this microscope?

Express your answer in nanometers to three significant figures.

ANSWER:	= 3.88×10−2

Compare this wavelength to the typical size of an atom.

 

Part B
Can an individual atom theoretically be resolved using this electron microscope?

ANSWER:	yes no

Note that in practice a resolution better than cannot be achieved with an electron microscope. This is due, in part, to the fact that the focal length of a magnetic lens depends on the electron speed, which is never the same for all electrons in the beam.

 

 

Part C
Suppose we replace the electron beam with a proton beam. What proton energy is needed to achieve the same resolution as the electron beam in Part A?

Express your answer in electron volts to three significant digits.

ANSWER:	0.545

In principle, we could use proton beams with relatively low energy to get great resolution. However, in practice, it is much easier to create an electron beam than it is to create a proton beam, which is why electron microscopes have become the norm.