Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Resolution of Microscopes
Name: Paul T.
Status: student
Age: 16
Location: N/A
Country: N/A
Date: 1999-2001


Question:
I was wondering why the electron microscope has a much higher magnification(500'000X) compared to a light microscope(1500X). The LM uses lenses to increase magnification but the electron microscope does not have lenses. My lecturer told me that it has something to do with resolving power. She said that since the resolving power of an EM is 0.5nm while the resolving power of a LM is 0.2um, the EM will perceive 2 pts as further apart and so the whole image will be enlarged. As I said, I thought magn was achieved with lenses?

I have learnt that the resolving power of a microscope is defined as the minimum distance by which 2 points must be separated in order for them to be perceived as 2 separate points rather than a fused image. From my understanding, the resolving power is the sharpness of a TV. but no matter how sharp a 21-inch TV is, 2 points on it, say, about 1 mm apart may not be perceived as separate, while the same points on a projection TV with the same sharpness may be seen as separate. Can anybody pls explain/clarify? Thanks. Sorry for the lengthy question.


Replies:
Paul - The short and simple answer to your long question is that the wavelength of light is greater than the wavelength of an electron. The shorter wavelength allows you to resolve points that are closer together.

Larry Krengel


Paul,

Besides the influence of lenses -- be they glass in an optical microscope or magnetic like those in an electron microscope -- the resolving power of a microscope is a function of the wavelength of the "light" used to illuminate the specimen being examined. The shorter the wavelength, the better the resolving power. The wavelength of blue light is shorter than red. Thus, resolving power is improved on any optical microscope if the light is more blue than red. The wavelength of electrons are much shorter than that of light of any color. For that reason and a few others, the electron microscope holds the advantage over an ordinary light microscope. However, not all specimens can be examined under an electron microscope. The why of this is the subject of another discussion.

Regards,
ProfHoff


I have learnt that the resolving power of a microscope is defined as the minimum distance by which 2 points must be separated in order for them to be perceived as 2 separate points rather than a fused image. From my understanding, the resolving power is the sharpness of a TV. but nomatter how sharp a 21-inch TV is, 2 points on it, say, about 1 mm apart may not be perceived as separate, while the same points on a projection TV with the same sharpness may be seen as separate. Can anybody pls explain/clarify? Thanks. Sorry for the lengthy question.

Vince Calder


The resolution limit depends on the wavelength and the quality of lenses. With perfect lenses, the achievable resolution is roughly equal to the wavelength. Visible light has a wavelength of around .5 micron; the electrons used in an electron microscope have such a small wavelength that it is not the limiting factor.

Tim Mooney



Click here to return to the General Topics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory