Glossary
Amperian Loop
An imaginary closed loop chosen strategically to apply Ampère's Law, where the magnetic field is either constant and parallel to the loop, or perpendicular to it, simplifying the integral.
Example:
When using Ampère's Law to find the magnetic field of a long wire, a circular Amperian loop centered on the wire is typically chosen.
Ampère’s Law
A fundamental law in electromagnetism that relates the circulation of a magnetic field around a closed loop to the total current enclosed by that loop.
Example:
Deriving the magnetic field inside a long solenoid is a classic application of Ampère’s Law.
Biot-Savart Law
A law that describes the magnetic field produced by an electric current, allowing for the calculation of the magnetic field at any point due to a small segment of current.
Example:
Calculating the magnetic field at the center of a current loop often involves integrating using the Biot-Savart Law.
Cross Product
A binary operation on two vectors in three-dimensional space that results in a vector perpendicular to both original vectors, with its magnitude related to the sine of the angle between them.
Example:
In calculating the torque on a current loop, we often use the cross product of the magnetic dipole moment and the magnetic field.
Cyclotron Motion
The circular path followed by a charged particle when it moves perpendicular to a uniform magnetic field, where the magnetic force provides the necessary centripetal force.
Example:
In a cyclotron, particles are accelerated in a spiral path due to a uniform magnetic field causing them to undergo cyclotron motion.
Diamagnetic materials
Materials that are weakly repelled by magnetic fields. This repulsion is due to a slight alignment of electron dipole moments opposite to the external field.
Example:
Water is a diamagnetic material, which is why a very strong magnetic field can cause a tiny, almost imperceptible repulsion, a phenomenon used in some levitation experiments.
Ferromagnetic materials
Materials that can be strongly magnetized and retain their magnetism, even becoming permanent magnets. They contain magnetic domains that align with an external field and remain aligned.
Example:
Iron is a ferromagnetic material, which is why it's used to make strong permanent magnets and cores for electromagnets.
Induced magnetism
The temporary magnetization of a material when it is placed within an external magnetic field. The material's dipoles align temporarily but return to random orientations once the field is removed.
Example:
When a paperclip is picked up by a strong magnet, it temporarily becomes magnetized through induced magnetism, but it loses its magnetism as soon as the strong magnet is removed.
Magnetic Field (from long wires)
The region of influence around a long, straight current-carrying wire, characterized by circular field lines whose strength decreases with distance from the wire.
Example:
Power lines generate a magnetic field around them, which is stronger closer to the wires.
Magnetic Force
The force experienced by a charged particle moving through a magnetic field, always perpendicular to both the particle's velocity and the magnetic field.
Example:
A proton entering a particle accelerator experiences a magnetic force that bends its path into a circle.
Magnetic Force (on current-carrying wires)
The force experienced by a segment of current-carrying wire placed within a magnetic field, resulting from the interaction between the moving charges in the wire and the external field.
Example:
The coils in an electric motor experience a magnetic force that causes them to rotate when current flows through them in a magnetic field.
Magnetic dipoles
The fundamental units of magnetism, consisting of a north and a south pole, always occurring together. They are often modeled as tiny current loops.
Example:
A tiny bar magnet or an electron's spin can be considered a magnetic dipole, creating its own localized magnetic field.
Magnetic field lines
Imaginary lines used to visualize the direction and strength of a magnetic field. They originate from the north pole and terminate at the south pole, forming closed loops.
Example:
Drawing magnetic field lines around a current-carrying wire helps visualize the circular pattern of the field, indicating its direction with arrows.
Magnetic monopoles
Hypothetical isolated north or south magnetic poles, analogous to isolated positive or negative electric charges. They have never been observed experimentally.
Example:
Despite extensive searches, scientists have never found a magnetic monopole, reinforcing the principle that magnetic poles always exist in pairs.
Magnetic permeability
A measure of how easily a material can support the formation of a magnetic field within itself. It indicates how much a material can be magnetized in response to an external magnetic field.
Example:
Materials with high magnetic permeability, like iron, are used in transformer cores to concentrate magnetic fields efficiently.
Paramagnetic materials
Materials that are weakly attracted to magnetic fields. Their magnetic dipoles align temporarily with an external field but return to random orientations when the field is removed.
Example:
Aluminum foil is a paramagnetic material; it will show a very slight, temporary attraction to a strong magnet, but it won't stick.
Permanent magnetism
The ability of a material to retain its magnetic properties even after the external magnetizing field is removed. This occurs due to the lasting alignment of magnetic domains.
Example:
A refrigerator magnet exhibits permanent magnetism, sticking to the fridge door indefinitely without an external power source.
Permeability of Free Space (μ₀)
A fundamental physical constant representing the ability of a vacuum to support the formation of a magnetic field, used in formulas for magnetic field strength.
Example:
The value of permeability of free space is essential when calculating the magnetic field inside a solenoid.
Right-Hand Rule (for current-carrying wires)
A mnemonic used to determine the direction of the magnetic force on a current-carrying wire, where the thumb points to current, fingers to the magnetic field, and the palm indicates the force.
Example:
When designing an electromagnet, you'd use the Right-Hand Rule to predict the direction of the force on the wire segments within the magnetic field.
Right-Hand Rule (for magnetic fields from wires)
A mnemonic used to determine the direction of the magnetic field lines around a current-carrying wire, where the thumb points in the direction of current and curled fingers indicate the direction of the field.
Example:
To determine if a compass needle will point clockwise or counter-clockwise around a current-carrying wire, you'd use the Right-Hand Rule to find the field direction.
Right-Hand Rule (for moving charges)
A mnemonic used to determine the direction of the magnetic force on a positive charge, where the thumb points to velocity, fingers to the magnetic field, and the palm indicates the force.
Example:
To find the direction a positive ion will deflect in a mass spectrometer, you'd apply the Right-Hand Rule with your thumb along the ion's velocity and fingers along the magnetic field.
Vacuum permeability (μ₀)
A fundamental physical constant representing the ability of a vacuum to permit magnetic field lines to pass through it. It is the baseline for magnetic permeability.
Example:
The constant vacuum permeability (μ₀) is used in Ampere's Law and the Biot-Savart Law to calculate magnetic fields in free space.
Vector field
A region in space where every point is associated with a vector quantity, indicating both magnitude and direction. Magnetic fields are an example of a vector field.
Example:
The gravitational field around Earth is a vector field, pulling objects towards its center with a strength dependent on distance.