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Physics help pleaseeeee!!

In a demonstration, electrons are going round in a 12cm diameter helix with the beam at 70 degrees to the 0.0032T magnetic field. Calculate the speed of the electrons.

I don't get how to do it, can someone help please! Much appreciated
Reply 1
Avatar for Rexar
Rexar
11
Force on electrons = centripetal force
(mv^2)/r = Bqv sin(theta)
Then rearrange
Reply 3
Avatar for Rexar
Rexar
11
F=mv^2/r. F=BQVsintheta or something, look at the equations sheets
(edited 7 years ago)
Using F = qvB, the F we want is actually Fsin(70), so Fsin(70) = qvB

But we also know for circular motion, F = mv^2/r (r = 0.06 as its radius, diameter is given), substitute into the first equation and rearrange for v.
Reply 5
Avatar for p.isnotcool
p.isnotcool
OP
2
Original post by -Phoenix-
(mv^2)/r = Bqv sin(theta)
Then rearrange


I tried that but the answer seems to be incorrect.
Original post by p.isnotcool
I tried that but the answer seems to be incorrect.


It may be that you have to do sin(20) as the magnetic field has to be perpendicular
Reply 7
Avatar for p.isnotcool
p.isnotcool
OP
2
Original post by fermion.
using f = qvb, the f we want is actually fsin(70), so fsin(70) = qvb

but we also know for circular motion, f = mv^2/r (r = 0.06 as its radius, diameter is given), substitute into the first equation and rearrange for v.


thank youuu i got it!
just use speed=distance over time

Original post by p.isnotcool
thank youuu i got it!
Original post by p.isnotcool
thank youuu i got it!


No problem x

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