The Effect of an Electric
Field on Moving Charges
Lab 29: The Effect of an Electric Field on Moving
To investigate the effect of a static electric ﬁeld on various moving charges
As scientists ﬁrst began investigating the properties of atoms, they discovered
that they could extract negatively charged particles. They called these particles
electrons. In order to understand the nature of these particles, scientists wanted
to know how much charge they carried and how much they weighed. J.J.
Thomson was a physics professor at the famous Cavendish Laboratory at
Cambridge University. In 1897, Thomson showed that if you could measure
how far a beam of electrons was bent in an electric ﬁeld and in a magnetic ﬁeld,
you could determine the charge-to-mass ratio (q/me) for the electrons. Knowing
this ratio, the individual charge and mass of an electron could be calculated.
Another particle ejected during nuclear decay is the alpha particle. An alpha
particle is a helium nucleus, that is, a helium atom without its two electrons. As
you will see, a beam of alpha particles can also be deﬂected by an electric ﬁeld.
Predicting, observing, drawing conclusions
1. Start Virtual Physics and select Effect of an Electric Field on Moving Charges
from the list of assignments. The lab will open in the Quantum laboratory.
2. The exper...