Ask A Scientist© Physics Archive

>
> > >    name         Robert
> > >    status       student
> > >    age          18
>
> > >    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
>
> > 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
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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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