phy4
Fundamentals of Magnetism
I. Definition of Terms
a. Magnet
- Definition: A magnet is defined as a material capable of interacting with other materials, easily influenced by magnetism.
- Etymology: The term 'magnet' originates from the ancient Greek place Magnesia, where most of the known lodestones were found in ancient times.
b. Magnetic Pole
- Definition: The magnetic pole of a magnet is the region that exhibits polar characteristics, meaning it has both a north and a south pole.
c. Magnetic Field
- Definition: A magnetic field is the field of force that surrounds a magnet.
- Creation: It is created from a changing electric field, which stems from the movement of electric charges.
- Direction: The orientation and direction of the magnetic field are determined by the right-hand rule, which provides a way to visualize the direction of the magnetic field relative to the current direction.
d. Lorentz Force
- Definition: The Lorentz force is the total force acting on a charged particle in an electromagnetic field, influenced by both electric and magnetic forces.
- Formula: The Lorentz force is represented by the equation:
- Special Case (Magnetic Force): Eliminating the electric field component leads to the expression for the magnetic force:
i. Electric and Magnetic Forces
Electric Force:
- Projection: The electric force acts in a direction parallel to the electric field.
- Effect on Charges: It causes a moving charge to change its direction in accordance with the electric field's projection.
Magnetic Force:
- Projection: The magnetic force operates perpendicular to the directions of both the electric field and the magnetic field.
- Effect: It changes the trajectory of a moving charge in a manner perpendicular to the magnetic field direction.
e. Cyclotron Radius
- Definition: The cyclotron radius represents the radius of the circular motion of a charged particle in a magnetic field.
- Formula:
f. Cyclotron Frequency
- Definition: The cyclotron frequency defines the angular frequency of a charged particle's circular motion in a magnetic field.
- Behavioral States:
- When the Lorentz force equals the magnetic force:
- If qvB > rac{mv^2}{r}, the charged particle moves in a spiral path, trapped within the magnetic field.
- If qvB < rac{mv^2}{r}, the movement is an arc as the particle escapes the field.
- If , the movement is circular.
- Formula:
g. Magnetic Flux
- Definition: Magnetic flux quantifies the strength of a magnetic field passing through a specific area.
- Unit: The unit for magnetic flux is the Weber.
- Conversion:
- Formula:
- Implication: In a closed surface, the total magnetic flux is equal to zero:
h. Solenoid
- Definition: A solenoid is a conducting wire coiled in a helical shape, functioning similarly to multiple single-loop conductors arranged in parallel.
i. Biot-Savart Law
- Definition: This law describes how a magnetic field is generated by changing electric fields and is consistent with both Ampere’s and Gauss’s Laws.
- Formula:
j. Ampere's Law
- Definition: Ampere's Law relates the current flowing through a conductor to the magnetic field it generates.
- Formula:
II. FORMULAE Variations
a. Biot-Savart Law Current Distribution
- Point in the Magnetic Field
- Long Straight Conductor:
- Long Cylindrical Conductor:
- Inside the conductor:
- Outside the conductor:
- Inside the conductor:
- Long Solenoid (nearly ideal), with number of loops per length:
- Inside the solenoid:
- Outside the solenoid:
- Inside the solenoid:
- Moving Charge:
- At distance:
- At distance:
- Circular loop with a specific radius:
- Loop as an arc with central angle (in radians):
- Center of complete loop at origin:
- Distance given (a) above or below origin:
- Loop as an arc with central angle (in radians):
- Long Straight Conductor:
b. Ampere's Law Shape of the Conductor Formula
- Ring / Toroid:
- Loop:
- Solenoid:
- Straight Wire:
References
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