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Name: Robert
Status: student
Age: 18
Location: N/A
Country: N/A
Date: 2000-2001


Question:
I read that the electron is a point particle. This makes sense if it is a fundamental particle, since if it had non-zero volume whatever it was made out of would be more fundamental.

The problem is, I thought the electron had mass--orders of magnitude smaller than the proton, but still a measurable mass...

Can a point particle that takes up no space have mass? How?

I suspect my assumptions are wrong somewhere.

cheers

Robert


Replies:
Good thinking, you suspect some assumption is wrong, and it is. The electron -- as a point charge -- is an approximation when observed from distances are much larger than atomic and molecular distances. At distances of the order of nanometers, atoms have a finite size. One hydrogen atom e.g. has a radius of ~5 nm, called the Bohr radius, and a sphere of this radius is about how much space the electron is occupies in a H atom because the proton is much much smaller. But when viewed up really close, even atomic nucleii have a volume.

A "point charge" is an approximation, a mental construction that is quite good for many cases. Except for the speed of light in a vacuum, I can't think of any physical quantities that aren't approximations on some scale, either very small or very large.

Vince Calder


I don't know the context in which you learned that the electron is a "point particle" but I don't think it was intended to imply that the electron has no volume. The electron is a member of a class of particles called fermions. Among other things, these particles exclude other fermions from their volume -- i.e. they have volume.

Bradburn



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