4.2.4.P8B
We know that within the limits of measurement, the magnitudes of the negative charge on the electron and the positive charge on the proton are equal. Suppose, however, that the magnitude of the charge on the proton was bigger than that on the electron by 1 part in a million. Estimate with what force two copper pennies, placed one meter apart, would then repel each other. You may find some of the following parameters useful (or not).
Here are some potentially useful parameters:
| kC (Coulomb's constant) ~9 ✕ 109 N-m2/C2 | e (charge on proton) ~1.6 ✕ 10−19 C |
| me (mass of electron) ~9 ✕ 10−31 kg | mp (mass of proton) ~1.7 ✕ 10−27 kg |
| mCu (mass of a copper atom) ~ 10−25 kg | Number of electrons in a copper atom = 29 |
Since pennies do NOT repel each other with any detectable force, what can you conclude about the charges on a proton and on an electron?
Joe Redish 8/7/11
Wolfgang Losert 10/14/12