In an experiment with cosmic rays, a vertical beam of particles that have charge

Question

In an experiment with cosmic rays, a vertical beam of particles that have charge of magnitude 3e and mass 12 times the proton mass enters a uniform horizontal magnetic field of 0.250 T and is bent in a semicircle of diameter 95.0 cm, as shown in Fig. E27.22 in the textbook.

Part A

Find the speed of the particles.

v =   (m/s)

Part B

Find the sign of particles' charge.

positive

negative

Part C

Is it reasonable to ignore the gravity force on the particles?

unreasonable

Part D

How does the speed of the particles as they enter the field compare to their speed as they exit the field?

Explanation / Answer

A)

magnetic force = centripetal force

Fb = Fc

q*v*B = m*v^2/r

q*B = m*v/r

q = 3e = 3*1.6*10^-19

r = 0.95/2 = 0.475 m

(3*1.6*10^-19*0.25) = (12*1.67*10^-27*v)/0.475

v = 2.8*10^6 m/s <<--answer

++++++++

B)

positive

C)

reasonable

D)

same

as the magnetic force is perpendicular . work done is zero . so the KE remains same

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