# V and eV

1. May 24, 2009

### lha08

1. The problem statement, all variables and given/known data
How can i convert V to eV in a problem?
I know that 1V=1.6X10^-19 J but I don't see how that can help...
Thanks.

2. Relevant equations

3. The attempt at a solution
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. May 24, 2009

### Dadface

I think you have got your question a bit muddled up.It is 1eV that is equal to 1.6x10^-19J.

3. May 24, 2009

### tiny-tim

Hi lha08!

V is voltage (potential difference), but eV is energy …

1 eV is the https://www.physicsforums.com/library.php?do=view_item&itemid=75" (ie energy) when an electron (whose charge you can look up ) moves through a potential difference of 1 V.

Last edited by a moderator: Apr 24, 2017
4. May 24, 2009

### lha08

So in this case, the charge of an electron is 1.60X10^-19 J...so is it impossible to convert eV to V? Not really sure...Thanks..

Last edited by a moderator: Apr 24, 2017
5. May 24, 2009

### lha08

Like for example, if the work function is 2.35 V (3.76X10^-19 J) and the wavelength is 2.30X10^-7 m (frequency=1.30*10^15 Hz), and asked to calculate the stopping potential.
In this case, i use the formula eVo=hf-(work function)
then eVo=4.88X10^-19 after plugging all the values.
Need to find Vo: do i just need to divide 4.88X10^-19 by e (the electron charge 1.6X10^-19 J) and the answer will be in volts?

6. May 24, 2009

### kbaumen

V (volts) measure potential difference (voltage). eV (electron volts) measure energy and can thus be converted to J (joules). V and eV measure two different things and therefore cannot be converted to each other.

Btw, an electron's charge is always $1.6 \cdot 10^{-19}$ C (coulombs). Coulomb, not joule, is the unit in which you measure charge.

7. May 24, 2009

### tiny-tim

Nooo … the charge of an electron is in coulombs (C).

J (joules) is energy.

As Dadface points out, you can convert eV to J (because they're both units of energy) …

but V and eV are not units of the same thing …

eg you can convert metres to feet, but you can't convert metres to feet per second.

8. May 24, 2009

### Dadface

I think you are still getting muddled up but let me try to guess what you mean by giving an example.Suppose an electron has an energy of XeV.If so one way it could acquire that energy is to be accelerated from rest through a p.d of X volts.As tiny tim said V and eV are different things.

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