High School Physics Overview Notes

Electrostatics

• Electric Charge: Matter possesses positive or negative electric charge $q = \pm n e$, where $e \approx 1.6 \times 10^{-19}\,\text{C}$ is the elementary charge.
• Law of Conservation of Charge: The total electric charge of an isolated system remains constant across all processes.
• Coulomb's Law: The electrostatic force between two point charges is given by $F = k \frac{|q_1 q_2|}{r^2}$, where k \approx 9 \times 10^9\,\text{N}\cdot\text{m}^2/\text{C}^2$.\n* **Electric Field & Potential:**\n * Field lines originate on positive charges and terminate on negative charges.\n * Electric potential V$defines potential energy per unit charge ($E_e = q V$). Voltage is potential difference$U = V_A - V_B$.
  • Work done by the electric field moving a charge: W = q U$.\n* **Conductors & Insulators in Fields:**\n * In electrostatic equilibrium, the internal electric field and voltage difference inside a conductor are zero (E = 0$,$U = 0); excess charges reside entirely on the outer surface, concentrating at sharp edges.\n * A *Faraday cage* shields its interior from external electric fields.\n * Insulators contain bound charges that form electric dipoles under external fields (polarization).\n* **Capacitors:**\n * Systems of two conductors separated by an insulator, characterized by capacitance C = \frac{q}{U}$(measured in farads,$\text{F}).\n * Stored electrical energy: E_e = \frac{1}{2} C U^2 = \frac{1}{2} q U$.

Electric Current

• Current Intensity: Defined as $I = \frac{q}{t}$, measured in amperes ($\text{A}$). Conventional current flows from higher to lower potential.
• Ohm's Law: Current intensity is proportional to applied voltage: $I = \frac{U}{R}$, where $R$ is resistance in ohms ($\Omega$).
  • Resistance of conductors increases with temperature; resistance of semiconductors decreases with temperature.
• Electric Work & Power:
  • Energy transformed in an electric receiver: E = U I t$.\n * Electric power: P = U I$, measured in watts ($\text{W}$) or kilowatt-hours ($1\,\text{kWh} = 3.6 \times 10^6\,\text{J}).\n* **Kirchhoff's First Law:** The sum of currents entering a circuit junction equals the sum of currents leaving it: \sum I_{\text{in}} = \sum I_{\text{out}}.\n* **Parallel Connections:** Voltage across parallel branches is identical (U$); total current$I = I_1 + I_2 + \dots$; total power$P = P_1 + P_2 + \dots\n* **Circuit Safety:** Residual-current devices (*bezpieczniki różnicowoprądowe*) disconnect power when leak currents exceed 30\,\text{mA}; circuit breakers (*bezpieczniki przeciążeniowe*) protect against short circuits and overloads.\n\n# Electromagnetism\n\n* **Magnetic Field & Induction:**\n * Magnetic field strength is characterized by magnetic induction \mathbf{B}$in teslas ($\text{T}). Field lines form closed loops.\n * *Ferromagnets* strongly magnetize in external fields and retain residual magnetization.\n* **Magnetic Forces:**\n * **Electrodynamic Force:** Acts on a current-carrying conductor in a magnetic field: F = B I l (for perpendicular orientation, direction given by the left-hand rule).\n * **Lorentz Force:** Acts on a moving charge q$:$F_L = q v B$(for perpendicular velocity). Alters particle direction without changing kinetic energy, resulting in circular motion with radius$r = \frac{m v}{q B}.\n* **Electromagnetic Induction & Waves:**\n * A changing magnetic field induces a swirling electric field and current in closed circuits (Faraday's Law of Induction).\n * Electromagnetic waves consist of coupled oscillating electric and magnetic fields propagating at light speed c \approx 3 \times 10^8\,\text{m/s}$($\lambda f = c).\n* **Alternating Current (AC) & Transformers:**\n * Effective values: U_{\text{sk}} = \frac{U_{\text{max}}}{\sqrt{2}}$,$I_{\text{sk}} = \frac{I_{\text{max}}}{\sqrt{2}}$. Average AC power:$P = U_{\text{sk}} I_{\text{sk}}.\n * Transformer voltage ratio: \frac{U_2}{U_1} = \frac{n_2}{n_1}.\n\n# Atomic Physics\n\n* **Electromagnetic Spectrum:** Encompasses radio waves, microwaves, infrared, visible light (400\,\text{nm} - 700\,\text{nm}), ultraviolet, X-rays, and gamma rays.\n* **Photons:**\n * Quantized light particles carrying energy E = h f = \frac{h c}{\lambda}$, where$h \approx 6.63 \times 10^{-34}\,\text{J}\cdot\text{s} is Planck's constant.\n * Energy unit conversion: 1\,\text{eV} = 1.6 \times 10^{-19}\,\text{J}.\n* **Atomic Structure & Energy Levels:**\n * Electrons occupy discrete energy levels (E_n).\n * Photon emission or absorption condition: h f = E_n - E_k$.
  • Thermal sources produce continuous spectra; non-thermal gas sources produce discrete line spectra.
• Band Theory & Semiconductor Devices:
  • Energy levels form energy bands (pasma energetyczne) separated by band gaps (przerwa energetyczna).
  • p-n Junction / Diode: Conducts current in one direction only. LEDs emit photons during electron transitions across the junction.
  • MOSFET Transistor: Uses gate voltage $U_{\text{GS}}$ to control current flow through a semiconductor channel.
• Photoelectric Effect:
  • Emission or excitation of electrons by light above a cutoff frequency $f_{\text{gr}} = \frac{W}{h}$, where $W$ is the work function.

Nuclear Physics

• Nuclear Structure:
  • Nucleus $_Z^A\text{X}$ contains $Z$ protons and $N = A - Z$ neutrons (nucleons).
  • Held together by strong, short-range nuclear forces.
  • Isotopes: Atoms of the same element with equal $Z$ but different A$.\n* **Radioactivity & Decay Law:**\n * Decay types: \alpha$(emission of$2^4\text{He}$),$\beta^-$(neutron converts to proton, electron$_{-1}^0 e$, and antineutrino),$\gamma (high-energy photon emission).\n * Radioactive Decay Law: N = N_0 \left(\frac{1}{2}\right)^n = N_0 \left(\frac{1}{2}\right)^{\frac{t}{T{1/2}}}$, where$T_{1/2} is the half-life.\n* **Dosimetry:**\n * Absorbed dose: D = \frac{E}{m}$in Grays ($\text{Gy}).\n * Equivalent dose in Sieverts (\text{Sv}$) incorporates biological effect ($1\,\text{Sv} = 1\,\text{Gy}$for$\beta, \gamma$;$1\,\text{Sv} = 0.05\,\text{Gy}$for$\alpha$). Average natural background:$\sim 2.5\,\text{mSv/year}.\n* **Binding Energy & Mass Deficit:**\n * Mass-energy equivalence: E_0 = m c^2$.
  • Mass deficit: $\Delta m = \sum m_{\text{nucleons}} - m_{\text{nucleus}}$.
  • Nuclear binding energy: $E_w = \Delta m \, c^2$. Peak binding energy per nucleon occurs near iron ($^{56}\text{Fe}$).
• Fission & Fusion:
  • Nuclear Fission: Heavy nuclei (e.g., $^{235}\text{U}$) split upon neutron absorption, releasing $\sim 200\,\text{MeV}$ and additional neutrons, sustaining a chain reaction above critical mass. Controlled in reactors using moderators and control rods.
  • Nuclear Fusion: Light nuclei combine (e.g., proton-proton chain $4\,^1\text{H} \rightarrow \,^4\text{He} + 2 e^+ + 2 \nu_e + \gamma$), releasing substantial energy; powers stars and thermonuclear reactors.
• Stellar Evolution & Compact Objects:
  • Stars fuse hydrogen to helium during main sequence.
  • Solar-mass stars expand into red giants, shed outer layers as planetary nebulae, leaving white dwarfs.
  • Massive stars ($> 9 M_{\odot}$) undergo core collapse, exploding as supernovae (synthesizing elements heavier than iron) and leaving neutron stars or black holes ($R_g = \frac{2 G M}{c^2}$).