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Name: Tania N.
Status: educator
Age: 30s
Location: N/A
Country: N/A
Date: 2001-2002

If a proton/neutron is very much larger than an electron, is a quark bigger or smaller than an electron? -- Question from one of my little year seveners. (grade~2)

Tania, A quark has never demonstrated any measurable size. Like an electron, it is a "fundamental particle", one of the few particles from which all else is made. The size of a proton or neutron comes from the motion of the quarks as they orbit around each other, sending energy and particles(called mesons) back and forth between each other. The three quarks are the primary particles of a proton/neutron, the particles that identify the proton or neutron for what it is. Still, the proton/neutron is essentially a cloud of motion with low energy particles flashing in and out of existence all the time. It is this cloud of motion that gives the proton/neutron its size.

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College

It takes "seveners" to ask those questions we wish we had asked in graduate school. The "size" of atomic and sub-atomic particles loses its meaning, because these "particles" behave as though they are waves, or wave packets. So "size" becomes kind of "squishy". However, with that caveat, the "classical" radius of a "free" electron is taken to be about 3x10^-15 meters, and the "classical" radius of a "free" proton is taken to be about 1x10^-15 -- only about 1/3 the radius of the electron. However, the "classical" radius of a hydrogen atom consisting of 1 proton and 1 electron, the Bohr radius, is about 5x10^-9 meters about one million times the radius of either component particle.

I do not know that anyone really thinks of quarks and other sub atomic particles as having a particular "size", in fact their masses are usually given in energy units of c^2 from the Einstein relation E = mc^2.


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