A cyclotron is a device used by physicists to study the properties of subatomic particles. Small charged particles are deposited at high speed into a circular pipe. Electric and magnetic fields then accelerate the particle to an even higher speed. Finally, when the particle reaches the desired speed, a magnetic field keeps it moving in a circle at constant speed.
In figure 1, a magnetic field pointing “into the page” keeps a charged particle traveling in a counterclockwise circle at constant speed inside the cyclotron. The magnetic force on the particle points towards the center of the circle, and has strength
Fmag = qvB,
where q is the particle's charge, v is its speed, and B is the magnetic field strength. As a result of this force, the particle circles the cyclotron at frequency
f =,
where m denotes the particle's mass. The frequency (in hertz) is the number of revolutions completed by the particle per second.
In the following questions, neglect gravity.
FIGURE 1

1. | In figure 1, what is the direction (if any) of the particle's acceleration?

A. | North

B. | East

C. | West

D. | It has no acceleration

2. | If the magnetic field in figure 1 were turned off, in which direction would the particle travel (until crashing)?

A. | North

B. | East

C. | West

D. | Nowhere; it would stop moving

3. | An alpha particle has charge 2e and mass 4 amu. A proton has charge e and mass 1 amu. Let falpha and fproton denote the frequencies with which those particles circle a cyclotron. If both particles experience the same magnetic field in the same cyclotron, what is?

A. | 2

B. | 1

C. | ½

D. | 1/4.

4. | In order for a cyclotron to work properly, the magnetic field must make the particle move in a circle. Which of the following particles would not work in a cyclotron?

A. | lithium atom (Li)

B. | positive lithium ion (Li+)

C. | negative lithium ion (Li–)

D. | all of the above particles would “work.”

5. | Which of the following cannot create a magnetic field?

A. | Electrical current flowing through a well-insulated straight metal wire.

B. | A beam of electrons moving across a cathode ray tube.

C. | Electric current flowing around a superconducting ring.

D. | Static electricity (i.e., extra electrons) built up on a stationary door knob.

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