PHYSICS 30 Magnetic Forces and Fields - Unit Review

1. If all electrons create magnetic fields, why aren’t all material magnets?

2. The diagram shows a bar magnet. On a copy of the diagram, show the magnetic lines of force at each end of the magnet.

3. A long, straight, current-carrying wire runs from north to south.

a) A compass needle that is placed above the wire points with its N-pole toward the east. In what direction is the current flowing?

b) If a compass is put underneath the wire, in which direction will the needle point?

4. A strong current is suddenly switched on in a wire. No force acts on the wire. Can you conclude with certainty that there is no magnetic field at the location of the wire? Explain.

5. An alpha particle experiences a downward force of 1.50 x 10-13 N when it is traveling at

7.80 x 104 m/s west through a magnetic field. What is the magnitude and direction of the magnetic field?

6. A magnetic field can exert a force on a moving charged particle. Can it change the particle’s kinetic energy? Explain.

7. A loop of wire is connected to a galvanometer. If a bar magnet is dropped through the loop, what happens to the galvanometer?

8. An electron enters a magnetic field of 0.300 T after being accelerated from rest by an unknown potential difference. If the magnetic force on the electron is 9.65 x 10-13 N, what is the magnitude of the accelerating potential?

9 . In a CRT, electrons are accelerated from rest by a potential difference of 1.55 x 103 V. These electrons enter a magnetic field with a strength of 0.0372 T. What is the radius of the arc of the deflected electrons?

1 0 . Explain what is meant by electromagnetic induction and describe two ways to induce a current or potential difference in a conductor.

1 1 . A conducting rod that is 40 cm long moves perpendicular to a magnetic field at a speed of 0.90 m/s. If the induced voltage is 0.090 V, what is the magnitude of the magnetic field?

1 2 . What happens to induced emf when magnetic field strength is doubled? Use any appropriate formulas in your explanation.

1 3 . The diagram shows a permanent bar magnet to the right of a solenoid connected to a battery with an unknown polarity. When the switch is closed, the magnet moves toward the right. Describe how you can determine the polarity of the battery.

14 . Diagram (1) shows a stationary, open-core solenoid connected to a galvanometer and diagram (2) shows the same solenoid after a north pole has been induced as shown.

In a few sentences, describe two ways of inducing the north pole shown in Diagram (2) using a permanent bar magnet on the right side of the solenoid.