# The magnetic field strength required to oscillate an electron

1. Apr 7, 2014

### cmcd

1. The problem statement, all variables and given/known data

"An electron is accelerated by a potential difference of 1 V and is injected into vacuum. How strong should the magnetic field in a vacuum be if you want the electron to circle along a loop with a radius of 10^-1m? Please indicate the direction of the magnetic field"

2. Relevant equations

PE = KE
for speed

F_centripetal =( mv^2) / r
for force

B = qv/F
for field strength

3. The attempt at a solution

v = sqrt(2qV/m)
v= 5.93 E5 m/s

F = 3.2 E-18 Newtons

B = 3 E4 Tesla

2. Apr 7, 2014

### cmcd

Not a textbook question...

3. Apr 8, 2014

### rude man

Better check that one.

4. Apr 11, 2014

### Staff: Mentor

It is a good practice to carry units along for all quantities in all of your equations. If you had done so, you would have caught this error that rude man is pointing out...

5. Apr 11, 2014

### rude man

I hope you listen to berkeman. There's nothing more important than carrying units along. Then you can check expressions term-by-term for agreement and the correctness of the answer. Which is (one reason) why I oppose using numbers instead of symbols until the very end, and why I abhor labeling e.g. a dependent voltage source as "10I" where I is current and the "10" is meant to be some impedance.