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AlexPilk
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Hi! I'm getting ready for an exam and want to make sure if I solved some problems correctly. I would be grateful for your feedback 
1. Homework Statement
After going through potential difference of 5000 V an electron falls in uniform magnetic field.
It’s induction is 0.1T and the electron’s speed is perpendicular to the lines of the magnetic field.
Find:
A. radius of the circle around which the electron will be moving
B. time it takes for the electron to travel one full circle.
K = eU = mv^2/2
F = mv^2/r = B*q*v
B = 0.1 T
U = 5000 V
Also if the electron is moving from left to right, and the magnetic field goes from top to bottom - Lorentz’s force would push it “into the screen”.
Since the kinetic energy of an electron K = eU = mv^2/2 we can find the speed.
e = 1.6*10^-19 J
m = 9.1*10^-31 kg
So v^2 = 2eU/m = (2*1.6*10^-19*5000)/(9.1*10^-31) = 1.75824176*10^15
v = sqrt(1.75824176*10^15) = 41931393.5 m/s
Because there’s centripetal magnetic force acting on the electron F = mv^2/r = B*q*v. Therefore r = mv/(B*q)
r = (9.1*10^-31*41931393.5)/(0.1*1.6*10^-19) = 2.38484801*10^-3 m
Or r = 2.38484801 mm.
To find the time we divide the length of the path by the speed, so
t = 2Pi*r/v = (2*3.14*2.38484801*10^-3)/41931393.5 = 3.57175001*10^-10 s
1. Homework Statement
After going through potential difference of 5000 V an electron falls in uniform magnetic field.
It’s induction is 0.1T and the electron’s speed is perpendicular to the lines of the magnetic field.
Find:
A. radius of the circle around which the electron will be moving
B. time it takes for the electron to travel one full circle.
Homework Equations
K = eU = mv^2/2
F = mv^2/r = B*q*v
The Attempt at a Solution
B = 0.1 T
U = 5000 V
Also if the electron is moving from left to right, and the magnetic field goes from top to bottom - Lorentz’s force would push it “into the screen”.
Since the kinetic energy of an electron K = eU = mv^2/2 we can find the speed.
e = 1.6*10^-19 J
m = 9.1*10^-31 kg
So v^2 = 2eU/m = (2*1.6*10^-19*5000)/(9.1*10^-31) = 1.75824176*10^15
v = sqrt(1.75824176*10^15) = 41931393.5 m/s
Because there’s centripetal magnetic force acting on the electron F = mv^2/r = B*q*v. Therefore r = mv/(B*q)
r = (9.1*10^-31*41931393.5)/(0.1*1.6*10^-19) = 2.38484801*10^-3 m
Or r = 2.38484801 mm.
To find the time we divide the length of the path by the speed, so
t = 2Pi*r/v = (2*3.14*2.38484801*10^-3)/41931393.5 = 3.57175001*10^-10 s
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