The device pictured above is called a velocity selector. Two charged plates are
ID: 1361197 • Letter: T
Question
The device pictured above is called a velocity selector. Two charged plates are placed in a uniform B-field, so that the direction of the E-field between them is at a right angle to the direction of the B-field. Charged particles are then sent through the plates. Only those for which the electrical and magnetic forces exactly cancel out are allowed to pass to the far end.
If we send hydrogen nuclei (that is, protons) into the selector with the strength of the E-field at 2000 N/C and the strength of the B-field at 0.8 T, what is their velocity if they make it through?
Question 2 options:
1600 m/s
2000 m/s
3100 m/s
2500 m/s
1000 m/s
1600 m/s
2000 m/s
3100 m/s
2500 m/s
1000 m/s
Explanation / Answer
Electric force = charge* electric field = 1.6*10-19*2000 N = 3.2*10-16 N
Force due to magnatic field = charge_q*Velocity_V*magnatic_field_B = Electric force (for particle to pass from parallel plates)
So V = Electric_force/(q*B) = 1.6*10-19*2000/(1.6*10-19*0.8) = 2500m/s Answer