E qV, where E energy, q the charge on the particle, V voltage across the field
When performing calculations involving the conversion of potential to kinetic energy or vice versa, we need to note: Loss in potential energy Gain in kinetic energy or
Gain in potential energy Loss in kinetic energy
ENERGY CONVERSION OF A CHARGED PARTICLE IN AN ELECTRIC FIELD
qV 1⁄2 mv2
q charge of the particle, V voltage through the particle it is accelerated, m mass of the particle, v velocity of the particle
SAMPLE PROBLEM 21B
The charge on one electron is 1.6 1019 C and its mass is 3.1 1031 kg. Calculate: (i) the energy in joules of 1 electronvolt (ii) the velocity of a electron that has 1 eV of kinetic energy.
SAMPLE ANSWER 21B
(i) Using the formulae for energy of a charge particle in an electric field, making sure all values are in their standard unit: E qV (1.6 1019 )(1) 1.6 1019
1 eV 1.6 1019 J (ii)
qV 1 2 mv2
1.6 1019 1 2 (9.1 1031)v2
The velocity of the electron 5.93 105 m s1. v A
2(1.6 1019) 9.1 1031 5.93 105
Thermionic Emission THERMIONIC EMISSION Thermionic emission is the emission of electrons from the surface of a hot metal. 378 INVESTIGATING PHYSICS
