Glossary
Combined Electric and Magnetic Forces
The total force experienced by a charged particle moving through a region where both an electric field and a magnetic field are present. The total force is the vector sum of the independent electric and magnetic forces.
Example:
In a velocity selector, combined electric and magnetic forces are balanced to allow only particles of a specific speed to pass through undeflected.
Hall Effect
The creation of a voltage difference (Hall voltage) across an electrical conductor, perpendicular to both an electric current flowing through the conductor and an applied magnetic field perpendicular to the current.
Example:
The Hall effect is utilized in sensors to measure the strength of magnetic fields or to determine the type of charge carriers in a semiconductor.
Magnetic Field
A region of space around a moving electric charge or a magnetic material where magnetic forces are exerted on other moving charges or magnetic materials. It is a vector quantity, possessing both magnitude and direction.
Example:
The Earth generates a magnetic field that protects us from harmful solar radiation.
Magnetic Force
The force experienced by a moving electric charge or a current-carrying conductor when placed in an external magnetic field. This force is always perpendicular to both the velocity of the charge and the magnetic field.
Example:
A charged particle entering a uniform magnetic field will experience a magnetic force that causes it to move in a circular path.
Magnetic Force Formula ($F_B = qvB\sin\theta$)
The mathematical equation used to calculate the magnitude of the magnetic force ($F_B$) on a charge ($q$) moving with velocity ($v$) in a magnetic field ($B$), where $\theta$ is the angle between the velocity and magnetic field vectors.
Example:
Using the magnetic force formula, we can calculate the force on an electron moving at 10^6 m/s perpendicular to a 0.5 T magnetic field.
Moving Charges Create Magnetic Fields
A fundamental principle stating that any electric charge in motion generates a magnetic field in the space surrounding it. The strength and direction of this field depend on the charge's velocity and position.
Example:
When electrons flow through a wire, they create a magnetic field around the wire, which can deflect a nearby compass needle.
Qualitative Analysis (Magnetic Force)
Describing the direction or general behavior of magnetic forces and particle motion without performing precise numerical calculations, especially for angles other than 0°, 90°, or 180°.
Example:
A qualitative analysis might involve sketching the path of a charged particle entering a magnetic field at an oblique angle.
Quantitative Calculations (Magnetic Force)
Calculations of magnetic force magnitude that are limited to specific angles (0°, 90°, and 180°) between the velocity and magnetic field vectors, simplifying the sine term in the force formula.
Example:
For quantitative calculations, an AP Physics 2 problem might ask for the force on a particle moving perpendicular (90°) to a magnetic field.
Right-Hand Rule (for magnetic field direction)
A mnemonic used to determine the direction of the magnetic field created by a moving positive charge. Point your thumb in the direction of velocity, fingers in the direction of the position vector, and your palm indicates the magnetic field direction.
Example:
To find the direction of the magnetic field produced by a proton moving upwards, you'd use the right-hand rule with your thumb pointing up.
Right-Hand Rule (for magnetic force direction)
A mnemonic used to determine the direction of the magnetic force on a positive moving charge. Point your thumb in the direction of velocity, fingers in the direction of the magnetic field, and your palm indicates the force direction. For negative charges, the force is in the opposite direction.
Example:
When a positive ion moves to the right in a magnetic field pointing into the page, the right-hand rule shows the magnetic force is directed upwards.
Strength of Magnetic Field
The magnitude of a magnetic field, which is stronger closer to the source and increases with the velocity of the moving charge creating it. It is measured in Tesla (T).
Example:
The strength of the magnetic field inside an MRI machine is very high, allowing for detailed medical imaging.