Capacitors, Magnets, and Electromagnetism Principles

Capacitor Function

A power capacitor stores electrical charge (electrons on one plate and ions on the other). Once charged, it maintains voltage due to electrostatic attraction. In DC circuits, it filters signals. In AC circuits, it charges and discharges in each half-cycle, delaying voltage relative to current, correcting the power factor.

Working Voltage and Breakdown

Working voltage is the maximum voltage a capacitor can withstand without dielectric damage. Breakdown voltage is the maximum voltage the dielectric can handle before failure.

Capacitor Types

• Plastic: Heavy-duty, up to 1000V, from several microfarads (µF).
• Ceramic: From picofarads (pF) to 100 nanofarads (nF), low voltage.
• Electrolytic: Polarized, high capacitance for small size (1 µF to tens of thousands µF), DC only, aluminum and tantalum.

Magnets

Magnets attract ferromagnetic materials (nickel, cobalt, iron). Applications: material separation, dynamos, speakers, microphones. Poles (N and S) are the strongest areas. Compass: A magnetic needle rotates freely, aligning with Earth's magnetic field.

Types: Natural (magnetite), Artificial (manufactured), Magnetized (steel), Permanent (long-lasting magnetic properties), Temporary (magnetic only when subjected to a field). Magnetic properties are altered by temperature and impacts.

Field Lines: Represent magnetic field intensity and direction.

Electromagnetism

Created by current flow, generating a magnetic field. Field line density is higher closer to the conductor. In a loop or coil, field lines concentrate at the center.

Magnetic Quantities

• Magnetic Flux (Φ): Φ = B * S (Magnetic induction * Surface area), measured in Webers (Wb).
• Magnetic Induction (B): Number of field lines per unit area, measured in Teslas (T).
• Magnetomotive Force (F): Ability of a coil to generate field lines, F = N * I (Number of turns * Current).
• Magnetic Field Strength (H): H = (N * I) / L (Magnetomotive force / Length), measured in Amperes per meter (A/m).
• Hopkinson's Law: Φ = F / Reluctance.

Magnetization Curve

Shows the relationship between magnetic induction (B) and magnetic field strength (H). Saturation: When B increases very little with increasing H.

Magnetic Permeability

Ability of ferromagnetic materials to amplify magnetic field lines.

Hysteresis

Residual magnetism in a ferromagnetic material after the external magnetic field is removed, causing energy loss as heat in motors and transformers.

1 Practical Solenoid Applications

Magnetic brakes, solenoid valves, buzzers, relays, and contactors.