Converting V to eV: A Problem Solving Guide

[lha08]

Homework Statement

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.

 

[Dadface]

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

 

[tiny-tim]

How can i convert V to eV in a problem?

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.

 

[lha08]

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.

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..

 

[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?

 

[kbaumen]

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..

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.

 

[tiny-tim]

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..

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.

 

[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.