Electromagnetism & Electric Charge

• Electromagnetism is one of the four fundamental forces of nature.
• The electromagnetic force is responsible for the interactions between charged particles.
• It manifests as electric and magnetic fields.
• Electromagnetism underlies many phenomena, including light, radio waves, and electrical devices.

Electric Charge

• Electric charge is a property of matter that causes it to experience a force when placed in an electromagnetic field.
• Two types of electric charge exist: positive and negative.
• Like charges repel, and opposite charges attract.
• The SI unit of electric charge is the coulomb (C).
• The elementary charge (e) is the magnitude of the charge carried by a single proton or electron, approximately 1.602 x 10^-19 C.
• Charge is conserved in a closed system, meaning the total charge remains constant.
• Charge is quantized, existing in integer multiples of the elementary charge (e).

Electric Field

• An electric field is a vector field that exists in the space surrounding an electric charge.
• It exerts a force on any other charged particle within the field.
• The electric field (E) at a point is defined as the electric force (F) per unit positive test charge (q₀): E = F/ q₀.
• The SI unit of the electric field is newtons per coulomb (N/C) or volts per meter (V/m).
• Electric field lines visualize electric fields, indicating the force direction on a positive test charge.
• Electric field lines originate from positive charges and terminate on negative charges.
• The density of field lines is proportional to the strength of the electric field.
• For a point charge q, the electric field at a distance r is given by Coulomb's law: E = k q/ r², where k is Coulomb's constant (approximately 8.9875 x 10^9 N⋅m²/C²).

Electric Potential

• Electric potential (voltage) is the electric potential energy per unit charge at a specific location in an electric field.
• It is a scalar quantity, measured in volts (V).
• The potential difference between two points is the work required to move a unit positive charge from one point to the other.
• Electric potential energy is the potential energy of a charged particle in an electric field, equal to the charge multiplied by the electric potential.
• Equipotential surfaces are surfaces where the electric potential is constant; no work is required to move a charge along such a surface.

Capacitance

• Capacitance measures a capacitor's ability to store electric charge.
• A capacitor consists of two conductive plates separated by an insulating material (dielectric).
• Capacitance (C) is defined as the ratio of the charge (Q) stored on the capacitor to the voltage (V) across it: C = Q/ V.
• The SI unit of capacitance is the farad (F).
• The energy stored in a capacitor is U = (1/2) C V².
• For a parallel-plate capacitor with plate area A and separation d, the capacitance is C = ε₀ A/ d, where ε₀ is the permittivity of free space (approximately 8.854 x 10^-12 F/m).
• Dielectric materials increase capacitance by reducing the electric field for the same charge.

Electric Current

• Electric current is the rate of flow of electric charge through a conductor.
• It is defined as the amount of charge (Q) passing a point per unit time (t): I = Q/ t.
• The SI unit of electric current is the ampere (A).
• Conventional current is the direction of positive charge flow, opposite to the direction of electron flow.
• Ohm's law states that the current (I) through a conductor is directly proportional to the voltage (V) and inversely proportional to the resistance (R): V = I R.
• Resistance (R) measures a material's opposition to current flow and is measured in ohms (Ω).
• Resistivity (ρ) is an intrinsic property that quantifies how strongly a material opposes electric current; Resistance is proportional to resistivity and length, and inversely proportional to cross-sectional area.

Magnetic Field

• A magnetic field is a vector field that exerts a force on moving electric charges and magnetic materials.
• Magnetic fields are produced by moving electric charges or intrinsic magnetic moments of elementary particles.
• The SI unit of magnetic field is the tesla (T).
• Magnetic field lines visualize magnetic fields, indicating the force direction on a moving positive charge.
• Magnetic field lines form closed loops, unlike electric field lines.
• Permanent magnets produce magnetic fields due to the alignment of atomic magnetic dipole moments.
• The magnetic force on a moving charge q with velocity v in a magnetic field B is given by the Lorentz force: F = q (v x B).

Electromagnetism

• Electromagnetism is the interaction between electric and magnetic fields.
• Moving electric charges create magnetic fields.
• Changing magnetic fields create electric fields (electromagnetic induction).
• The relationship between electricity and magnetism is described by Maxwell's equations.
• Maxwell's equations form the foundation of classical electromagnetism.
• Electromagnetic waves are disturbances in electric and magnetic fields that propagate through space, carrying energy.
• Radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays are examples of electromagnetic waves.
• Electromagnetic induction is the process by which a changing magnetic field induces a voltage (electromotive force) in a circuit.
• Faraday's law of induction states that the induced electromotive force (EMF) in any closed circuit equals the negative of the time rate of change of the magnetic flux through the circuit.
• Lenz's law states that the direction of the induced current opposes the change in magnetic flux that produces it.

Inductance

• Inductance is the property of a circuit element to oppose changes in current.
• An inductor typically consists of a coil of wire.
• Changing the current through an inductor induces a voltage across it.
• Inductance (L) is defined as the ratio of the magnetic flux linkage to the current (I): L = Φ/ I.
• The SI unit of inductance is the henry (H).
• The energy stored in an inductor is given by U = (1/2) L I².

Maxwell's Equations

• Maxwell's equations describe the behavior of electric and magnetic fields and their interactions.
• Gauss's law for electricity relates the electric field to the distribution of electric charge.
• Gauss's law for magnetism states that there are no magnetic monopoles.
• Faraday's law of induction describes how a changing magnetic field creates an electric field.
• Ampère-Maxwell's law describes how a magnetic field is generated by both electric current and a changing electric field.
• Maxwell's equations predict the existence of electromagnetic waves and determine the speed of light.