1. (3 pts) Five charged particles enter a magnetic field (into the page) as show

Question

1. (3 pts) Five charged particles enter a magnetic field (into the page) as shown. All have the same speed and mass. Explain your answer for each of the parts below.

a) Which one(s) has zero charge?

b) Which one(s) has negative charge?

c) Which one(s) has the largest charge?

2. A mass spectrometer can be used to separate out particles of different q/m ratio. Recall we talked about a mass spectrometer that used an electric field in our first homework problem. Here we will use a different type of mass spectrometer that separates out the particles using a magnetic field. A 238U ion (it has lost one electron) enters a magnetic field of 4.5 T with a speed of 3.5 *10^4 m/s and strikes a detector at a distance d from where it enters as shown.

a) (2 pts) Calculate the force on the 238U ion.

b) (2 pts) Calculate the value of d.

c) (1 pts) What is the new value of d if the charge on the ion is doubled?

3. (2 pts) What electric field (direction and magnitude) will make the path of the ion a straight line?

Explanation / Answer

1) a) A and C since they move straight

b) D

c) B and E
2

a) F = q v B = 1.6E-19*3.5E4*4.5=2.52E-14 N

b) q v B = mv^2/r

r = m v/(q B)

d = 2 r = 2 m v/(q B) = 2*3.95E-25*3.5E4/(1.6E-19*4.5)= 0.0384 m

c) then d is halved

so d = 0.0192 m

3) q v B = q E

E = v B = 3.5E4*4.5=157500 N/C upwards

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