Bloody electron volts (1 Viewer)

[NSBHSchoolie]

"X-rays are created by accelerating electrons from a cathode across a potential difference of 60000V. Find: the energy of each electron (in eV and J)."

Ok the answers respectively are 60000eV and 9.6x10^-15J

My question is how can the voltage be the same amount as the electron charge tacked on? Then the joules calculation comes from the charge on the electron multiplied by the voltage!

I might be missing something simple but this is really bugging me, because I know eV are sometimes used instead of J in the photoelectric effect calcs and I don't really understand it.

 

[wogboy]

An electron volt (eV) is simply another unit of measurement for energy, or work done.

1 eV = 1.6 * 10^-19 J

The electron volt is simply defined as "the work done to accelerate ONE electron by a voltage of ONE volt".

That question just uses the formula W = QV (where W = energy/work done in Joules, Q = charge in Coulombs, V = voltage in Volts). All you need to do is to apply the formula to get the answer in Joules, then convert to electron volts.

Sometimes it is more convenient to use the eV unit of measurement than the Joule, especially when dealing with very very small quantities of energy (e.g. the nuclear energy stored in one uranium-238 nucelus etc)

 

[NSBHSchoolie]

thanks