An electron is just like any other piece of matter; it has mass and therefore,when moving, has kinetic energy.The amount of energy depends only on how fast it is travelling as the mass of an electron is a constant.
An electric field can be used to accelerate an electron, giving the electron its kinetic energy; the amount of energy depends on the strength of the electric field.
The electronvolt
The amount of energy associated with individual electrons is so small that it is often more convenient to express it using a unit called the electronvolt (eV) rather than the joule.
1 eV is the amount of energy gained or lost by an electron when it moves through a potential difference of 1 V.
1 eV 1.6 1019 J
Because the unit eV is so small, it is often more convenient to use: kiloelectronvolt 1 keV 1 000 eV megaelectronvolt 1 MeV 1 000 000 eV
103 eV 106 eV
gigaelectronvolt 1 GeV 1 000 000 000 eV 109 eV
Converting electronvolts to joules Energy (given in joules) [Energy (given in electronvolts)] 1.6 1019 E( J) E( eV) 1.6 1019
SAMPLE PROBLEM 21A What is the energy of 5.6 MeV in joules?
SAMPLE ANSWER 21A M.6 megaelevtronvolts is equivalent to 8.96 1013 joules.
Energy Conversions Based on the definition of potential difference (work done in moving unit charge), it is clear that work (or energy) is equal to the product of voltage and charge.
V W Q QW VQ
In the case of an electron moving through a voltage V, the charge Q is equal to the charge on one charged particle (q).
We can therefore express the energy of a charged particle, due to its position in an electric field, as:
