??? 01 2. (14 points) A beam of protons is sent through a velocity selector, whi

Question

??? 01 2. (14 points) A beam of protons is sent through a velocity selector, which consists of a set of crossed electric and magnetic fields. With the protons moving due south, the selector consists of an upward electric field of intensity 2500 V/m and a magnetic field of 0.200 T to the west. a. Find the speed needed for the protons to pass through the fields undeflected b. Suppose protons at a speed (different from that of part a) of 9.00 x 10' m/s make up the beam. Find the net force (a vector) acting on one of these protons the instant it enters the fields. 3. (15 points) A wire loop in the shape of a square of side length 15.0 cm lies initially in an inward directed magnetic field of intensity 0.70 T, as shown. The region just to the right of the loop has

Explanation / Answer

In the velocity selector

magnetic force Fb = q*v*B

Electric force Fe = q*E

the protons pass undeflected

Fnet = 0

Fe = Fb

q*E = q*v*B

speed v = E/B

speed v = 2500/0.2 = 12500 m/s

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magnetic force Fb = q*v*B = 1.6*10^-19*9*10^3*0.2 = 2.88*10^-16 N ( downwards)

Electric force Fe = q*E = 1.6*10^-19*2500 = 4*10^-16 N ( Upwards)

net force Fnet = Fe - Fb = 1.12*10^-16 N

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