http://www.ck12.org Chapter 16. Electric Potential
The net force on the electron must be zero, thus
∑F=^0 →eF=mg→F=
mg
e
but F=eE→mg
e
=eE→E=mg
e^2→
E=
( 9. 11 × 10 −^31 kg)(
9. 81 ms 2)
( 1. 60 × 10 −^19 C)^2
= 3. 49 × 108
V
mhttp://www.youtube.com/watch?v=wT9AsY79f1k
The Electron-Volt
It is often convenient when dealing with small particles such as electrons, protons, and ions to express the energy
of these particles with a smaller unit of measure. The electron-volt is defined as the change in potential energy that
an electron acquires when moving through a potential difference of 1V,or equivalently, its change in kinetic energy
after moving through a potential difference of 1V.
That is,PE=eV= ( 1. 60 × 10 −^19 C)( 1. 00 V) = 1. 60 × 10 −^19 J.
The energy 1. 60 × 10 −^19 Jis defined as one electron-volt. We write one-electron-volt as 1eV= 1. 60 × 10 −^19 J.
Check Your Understanding
- What is the change in kinetic energyKEwhen an electron is released at the negative plate of a parallel plate
conductor with a potential difference of 3,500 V? Express your answer in eV.
Answer: The electron is repelled at the negative plate and therefore gains kinetic energy (and loses potential energy).
The change inKEis positive and equal to
1 eV
1 V=
x eV
3 , 500 V
→x= 3 , 500 eV∆KE= 3 , 500 eV