A uniform magnetic field of magnitude 0.167 T is directed along the positive x a
ID: 1260479 • Letter: A
Question
A uniform magnetic field of magnitude 0.167 T is directed along the positive x axis. A positron moving at 4.99E+6 m/s enters the field along a direction that makes an angle of 61.3deg with the x axis (see figure below).
The motion of the particle is expected to be a helix. The mass of a positron is the same as that of an electron: 9.11e-31 kg. The charge is +1.6e-19 C.
a) Calculate the pitch p of the trajectory.
b) Calculate the radius r of the trajectory.
Explanation / Answer
Here ,
v = 4.99 *10^6 m/s
B = 0.167 T
a) Now , time period of motion = 2*pi*m/Be
T = 2*pi*9.1 *10^-31/(e * 0.167)
T = 2.14 *10^-10 s
Now , pitch = t*v*cos(theta)
pitch = 4.99 *10^6 * cos(61.3) * 2.14 *10^-10
pitch = 5.13 *10^-4 m
B)
Now ,
r = mv/Be
r = 9.1 *10^-31 * 4.99 *10^6 * sin(61.3) /(0.167 * e)
r = 1.49 *10^-4 m
the radius of trajectory is 1.49 *10^-4 m
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