# Homework Help: Converting eV to Joules vs eV to V

1. Mar 26, 2015

### grandpa2390

1. The problem statement, all variables and given/known data
Is this true?

2. Relevant equations
1 eV = 1.6e-19 J
1 V = 1.6e-19 eV

3. The attempt at a solution

I did a bit of googling and it just seems strange.
eV multiplied by elementary charge = Joules
ev divided by elementary charge = Volts

2. Mar 26, 2015

### SteamKing

Staff Emeritus
This is correct: 1 eV = 1.6e-19 J

This is not correct: 1 V = 1.6e-19 eV

http://en.wikipedia.org/wiki/Electronvolt

An electron volt is a certain amount of energy, not voltage. By definition, 1 electron volt is the amount of energy it takes to move 1 electron across a potential difference of 1 volt.

3. Mar 26, 2015

### grandpa2390

By definition, it is the amount of energy gained (or lost) by the charge of a single electron moved across an electric potential difference of one volt. Thus it is 1 volt (1 joule per coulomb, 1 J/C) multiplied by the elementary charge (e, or 1.602176565(35)×10−19 C).
this is from the wikipedia page. what does this mean then if it is not saying one electron-volt is equal 1.6e-19 C * 1 Volt

based on that, 1 ev / 1.6e-19 C = 1 Volt, right? or am I missing something?

edit: or was issue not with the conversion, but with the units in my question?
1 Volt = 1.6e-19 C*eV rather than what I wrote: 1.6e-19 eV

if that be the case, my apologies, I was being hasty with my concern more for the conversion factor than the proper units.

4. Mar 26, 2015

### grandpa2390

The reason I am asking is because I have to calculate the the potential difference an electron would have to be accelerated through to give it a certain wavelength.
so far I have the potential difference = to the kinetic energy divided by 1.6e-19. but that would give a potential difference in electron volts. to convert to volts, shouldn't i divide again by 1.6e-19 Coulombs?

edit: I don't know I am reading something that says an electron gains 1 ev per 1 volt of potential difference. so maybe they are equal for one electron. this is all very confusing.

Last edited: Mar 26, 2015
5. Mar 26, 2015

### SteamKing

Staff Emeritus
1 electron volt already assumes a potential difference of 1 volt. Since 1 eV ≈ 1.602×10-19 joules, then divide the kinetic energy in joules by 1.602×10-19 to convert the KE of the electron into electron volts. This number will also be the voltage required to accelerate 1 electron such that it has that wavelength.