📖 Notes
LESSON 13 OF 17
Three Topics, One Lesson
Three Topics, One Lesson
Wave properties and Snell's law, then a fast circuits primer — Ohm's law, series/parallel resistance, and Kirchhoff's laws.
Waves
Wave Properties & Snell's Law
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Sound Waves
Longitudinal — particles vibrate parallel to travel direction. Needs a medium; can't travel through vacuum.
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Light Waves
Transverse — vibrations perpendicular to travel direction. Needs no medium, so it crosses empty space.
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Snell's Law
n₁sinθ₁ = n₂sinθ₂ — describes how light bends when crossing between two media of different density.
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Wave Equation
v = fλ links speed, frequency and wavelength for every wave type, sound or light.
- v = fλ · T = 1/f
- Sound: longitudinal wave, requires a medium
- Light: transverse wave, no medium required
- Snell's Law: n₁sinθ₁ = n₂sinθ₂
Electricity Primer
Circuits Reference
REFERENCEOhm's law: V = IR Power: P = VI = I²R = V²/R Series: R_total = R1 + R2 + ... Parallel: 1/R = 1/R1 + 1/R2 + ...
Kirchhoff's Laws
- 1st law (junction rule): total current in = total current out at any junction
- 2nd law (loop rule): the sum of voltage changes around any closed loop equals zero
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Exam tip
Series and parallel resistance formulas are easy to mix up under time pressure — series resistances simply add, while parallel resistances combine via their reciprocals. Sanity-check: parallel resistance is always smaller than the smallest individual resistor.