1. Physical Modeling, Fall 20061 THE MAGNETIC FIELD B is the symbol for the magnetic field. Magnetic field lines run from north poles to south poles. Like poles repel, and unlike poles attract. Poles cannot be isolated. They occur only in pairs, as dipoles.

2. Physical Modeling, Fall 20062 Charges in a Magnetic Field Moving charges experience a force due to a magnetic field. F B = qv × B where  is the angle between v and B. Direction is from the right hand rule. Magnitude of F B is: F B = qvB sin 

3. Physical Modeling, Fall 20063 Direction of the Magnetic Force

4. Physical Modeling, Fall 20064 Charges in a Magnetic Field The magnetic force on a moving charge is perpendicular to the direction of the magnetic field, and perpendicular to the direction of the velocity of the charge. If a charge moves parallel to the direction of a magnetic field, it experiences no magnetic force.

5. Physical Modeling, Fall 20065 Charges in a Magnetic Field If a charge moves perpendicular to a uniform magnetic field, it will travel in a circular path.

6. Physical Modeling, Fall 20066 Application Earth’s magnetic field shields us from incoming charged particles. However, since Earth’s magnetic field goes from the south pole to the north, particles can travel parallel to the field and enter the atmosphere near the poles. The “aurora” is the result.

7. Physical Modeling, Fall 20067 Aurora

8. Physical Modeling, Fall 20068 Frequency or Period Frequency or period of a circular orbit in a magnetic field does not depend on radius.

9. Physical Modeling, Fall 20069 Frequency or Period