Glossary
Amperes (A)
The SI unit for electric current, representing one Coulomb of charge passing a point per second.
Example:
A standard household light bulb might draw about 0.5 Amperes of current when turned on.
Angle ($ heta$)
The angle between the direction of the current in a wire and the direction of the external magnetic field, which determines the magnitude of the magnetic force.
Example:
If a wire's current is parallel to the magnetic field, the angle is 0 degrees, resulting in no magnetic force on the wire.
Concentric circles
Describes the shape of the magnetic field lines that form around a long, straight current-carrying wire, with the wire at the center.
Example:
If you sprinkle iron filings around a straight wire with current, they would arrange themselves into perfect concentric circles, revealing the magnetic field's pattern.
Current (I)
The rate of flow of electric charge through a conductor, measured in Amperes.
Example:
Increasing the current flowing through a wire makes the magnetic field it produces stronger, which is why high-power devices need thicker wires.
Current loop
A circular path through which electric current flows, creating a magnetic field that resembles that of a small bar magnet.
Example:
The magnetic field at the center of a current loop is strongest and points along its axis, making it useful in devices like solenoids.
Current-carrying wire
A conductor, typically a wire, through which electric current is flowing, thereby generating a magnetic field around it.
Example:
The electromagnet in a junkyard uses a powerful current-carrying wire wrapped around an iron core to lift heavy metal objects.
Distance (r)
In the context of a straight wire, it is the perpendicular distance from the wire to the point where the magnetic field is being measured.
Example:
The magnetic field from a power line weakens rapidly as your distance from it increases, becoming negligible far away.
External magnetic field
A magnetic field that originates from sources outside the system or object being considered, influencing its behavior.
Example:
A speaker's cone moves because the current in its voice coil interacts with the strong external magnetic field produced by a permanent magnet.
Length ($\ell$)
The segment of a current-carrying wire that is immersed within and perpendicular to an external magnetic field, contributing to the magnetic force.
Example:
To maximize the force on a wire in a magnetic field, you want to ensure the greatest possible length of the wire is exposed to the field.
Magnetic Field
A region of space around a moving electric charge or a magnetic material where magnetic forces are exerted on other moving charges or magnetic materials.
Example:
When you bring a compass near a bar magnet, the compass needle aligns with the invisible lines of the magnetic field created by the magnet.
Magnetic Field Strength (B)
A quantitative measure of the intensity of a magnetic field at a given point, indicating how strong the magnetic force would be on a moving charge or current.
Example:
A powerful MRI machine generates an incredibly high magnetic field strength to create detailed images of the human body.
Magnetic Force ($F_B$)
The force experienced by a current-carrying wire or a moving charge when placed within an external magnetic field.
Example:
Electric motors operate on the principle of magnetic force, where current-carrying coils experience a torque in a magnetic field, causing rotation.
Net magnetic field
The vector sum of all individual magnetic fields present at a specific point due to multiple sources.
Example:
When two wires carry current near each other, you must calculate the net magnetic field at any point by adding the individual fields as vectors.
Newtons (N)
The SI unit for force, defined as the force required to accelerate a mass of one kilogram at a rate of one meter per second squared.
Example:
The magnetic force on a wire in a strong field might be measured in a few Newtons, enough to cause noticeable movement.
Permeability of free space ($\mu_0$)
A fundamental physical constant that represents the ability of a vacuum to permit magnetic field lines to pass through it.
Example:
The constant permeability of free space is essential for calculating magnetic fields in a vacuum, much like the permittivity of free space is for electric fields.
Right-Hand Rule #1 (RHR1)
A mnemonic rule used to determine the direction of the magnetic field around a current-carrying wire: point your thumb in the direction of current, and your fingers curl in the direction of the magnetic field.
Example:
To figure out which way the magnetic field circles a straight wire, you'd use Right-Hand Rule #1, imagining you're grabbing the wire.
Right-Hand Rule #2 (RHR2)
A mnemonic rule used to determine the direction of the magnetic force on a current-carrying wire: point fingers in current direction, palm towards magnetic field, and thumb points to force direction.
Example:
When designing an electric motor, engineers use Right-Hand Rule #2 to predict the direction of the force that will spin the rotor.
Tangent
The direction of the magnetic field vector at any point is always tangent to the magnetic field line passing through that point.
Example:
A tiny compass placed near a current-carrying wire will always point in a direction tangent to the circular magnetic field line at its location.
Teslas (T)
The SI unit for magnetic field strength, named after Nikola Tesla.
Example:
A typical refrigerator magnet has a magnetic field strength of about 0.01 Teslas, while an MRI machine can generate several Teslas.
Vector Addition
The process of combining two or more vector quantities (which have both magnitude and direction) to find a single resultant vector.
Example:
To find the total magnetic field at a point due to two nearby wires, you must use vector addition to combine their individual magnetic fields.