Finding velocity from change in potential

[Xender]

I seem to be drawing a blank here (even though i have done these types of problems before).
Just need some help with remembering how to find the velocity of (an electron) when giving the change in potential.

 

[G01]

Think in terms of conservation of energy.

How much does the kinetic energy of the electron change by when it moves through the given voltage? You should be able to find the new velocity if you find the new kinetic energy.

 

[Xender]

oh nice thank you. yea i have that an electron is accelerated from rest through a potential difference of 400 V. so the KE at the start is 0 and initial PE is 400, so i ended up setting 400 = KE and solved.

 

[G01]

No problem.

Remember that potential is potential energy per unit charge. i.e.:

$$\Delta U=q\Delta V$$

where delta V is the potential difference and delta U is the difference in potential energy.

If you set the potential energy = 400, your units are in eV not J. Multiply the potential difference by the charge of the electron to get the energy in Joules if needed.