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As shown in the figure, an electron is fired with a speed of 3.43 Times 10^6 m/s

ID: 1422737 • Letter: A

Question

As shown in the figure, an electron is fired with a speed of 3.43 Times 10^6 m/s through a hole in one of the two parallel plates and into the region between the plates separated by a distance of 0.22 m. There is a magnetic field in the region between the plates and, as shown, it is directed into the plane of the page (perpendicular to the velocity of the electron). Determine the magnitude of the magnetic field so that the electron just misses colliding with the opposite plate. How is the magnetic force on a moving charged object related to the magnitude of the charge on the object, the speed of the object, the magnitude of the magnetic field experienced by the object, and the angle between the direction of the velocity of the object and the magnetic field? What type trajectory does a particle move in when it experiences a force perpendicular to its motion? How is the separation between the plates related to the trajectory of the electron?

Explanation / Answer

It will not hit the oppsoite plate, if it turns back just before hitting

electron will move in circular path in presence of magnetic field
It will not hit the opposite plate if radius of this circle is d = 0.22 m

use:
Force on electron = centrepetal force
q*v*B = m*v^2/r
r = m*v/(q*B)
0.22 = (9.1*10^-31)*(3.43*10^6) / (1.6*10^-19*B)
B = 8.87*10^-5 T
Answer: 8.87*10^-5 T