Physics

Electromagnetism and modern physics

Charge, fields, basic circuits, photons, mass–energy.

Basics

Charge and fields

Charge is measured in coulombs. Like charges repel; unlike attract. Electric field is force per unit charge. Magnetic fields act on moving charges (currents).

Quantum and relativity sketch

Light comes in photons E=hf. Atoms have discrete energy levels. E=mc² says mass is energy. The photoelectric effect showed light delivering energy in particle-like packets.

Formulas

Coulomb's law

F = k |q₁ q₂| / r², k = 1/(4πϵ₀)

Force between point charges. Same distance law as gravity, far stronger.

Symbols

q charge (C)
ϵ₀ vacuum permittivity

Electric field

E = F / q, 점전하: E = k |Q| / r²

Direction is the force on a positive test charge.

Ohm's law

V = I R

Voltage proportional to current in many metals. See electrical engineering for circuits.

Symbols

V voltage (V)
I current (A)
R resistance (Ω)

Photon energy

E = h f = h c / λ

Higher frequency (shorter wavelength) means more energy per photon.

Symbols

h Planck’s constant
c speed of light

Mass–energy

E = m c²

Rest energy. In nuclear reactions, mass defect appears as energy.

de Broglie wavelength

λ = h / p

Matter has a wave aspect. Basis of electron diffraction.

Symbols

p momentum

In this field

Mechanics

Kinematics, Newton, momentum, circular motion.

Energy and work

Work, kinetic and potential energy, power, conservation.

Waves and thermodynamics

Oscillation, waves, sound, heat, entropy.

Fluids and optics

Pressure, buoyancy, Bernoulli, lenses, interference.

Relativity and nuclear sketch

Time dilation, length contraction, decay, cross-section.

Quantum sketch

Photons, matter waves, uncertainty.

Gravity and orbits

Newton's gravity, Kepler, surface g, and circular orbits.

Rotation

Angular velocity, moment of inertia, torque, angular momentum, rolling.

SHM and resonance

Springs and pendulums, energy swap, damping, driving, and resonance.

Electrostatics

Coulomb force, electric field, potential, and a Gauss-law sketch.

Magnetostatics

Lorentz force, Biot–Savart, Ampère, and the solenoid.