🌈 Physics III: Waves, Heat & Light

What you’ll learn

1. Oscillations and Simple Harmonic MotionDefine simple harmonic motion and explain why pendulums and other oscillators keep reliable time.A restoring force proportional to displacement produces simple harmonic motion, whose period for a pendulum depends only on length and gravity. From Huygens's pendulum clock to quartz crystals and cesium atoms, timekeeping is the art of counting ever-steadier oscillations.
2. The Anatomy of a WaveDescribe waves by wavelength, frequency, and amplitude, and distinguish transverse from longitudinal waves.Waves carry energy through a medium that itself stays put, and speed always equals frequency times wavelength. Transverse waves oscillate across the direction of travel (light, a shaken rope); longitudinal waves compress along it (sound).
3. Sound: Pressure on the MoveExplain sound as a pressure wave, its speed in different media, and uses of ultrasound.Sound is a longitudinal pressure wave needing a medium, traveling about 343 m/s in room-temperature air — hence the flash-to-thunder counting rule. Human hearing spans roughly 20 Hz to 20 kHz; ultrasound above that range powers medical imaging, sonar, and bat echolocation.
4. Resonance and the Physics of MusicUse standing waves and resonance to explain pitch, timbre, and resonance disasters.Strings and air columns vibrate only in standing-wave patterns that fit their length, defining pitch; the mix of harmonics gives each instrument its timbre. Resonance pumps energy into a natural frequency — beautifully in instruments, destructively in the 1940 Tacoma Narrows collapse driven by aeroelastic flutter.
5. The Doppler Effect and Sonic BoomsExplain Doppler shifts for moving sources and what sonic booms and galactic redshift share.Motion compresses waves ahead of a source and stretches them behind, shifting pitch and color — Doppler's 1842 insight. At the speed of sound the waves pile into a shock cone heard as a sonic boom, and stretched light from receding galaxies (redshift) revealed the expanding universe.
6. What Temperature Really IsDefine temperature in molecular terms and relate the Celsius, Fahrenheit, and Kelvin scales.Temperature measures the average kinetic energy of molecules; thermometers read its effects, such as thermal expansion or buoyancy. The Kelvin scale starts at absolute zero (−273.15 °C), the unreachable floor of molecular motion that laboratories now approach within billionths of a degree.
7. Heat Is EnergyState that heat is energy in transit and explain specific heat with Joule's experiment.Joule's paddle-wheel experiment showed mechanical work converts to heat at a fixed rate, ending the caloric-fluid theory. Materials differ in specific heat; water's exceptionally high value (about 4,186 J/kg·°C) moderates coastal climates and makes oceans Earth's heat reservoir.
8. Conduction, Convection, RadiationDistinguish conduction, convection, and radiation and identify each in daily life.Conduction passes heat molecule-to-molecule (fastest in metals with free electrons), convection moves heat by circulating fluid (sea breezes, cumulus clouds, mantle flow), and radiation carries it as electromagnetic waves that cross even vacuum — how sunlight reaches Earth and how thermal cameras see.
9. Expansion and Changes of StateExplain thermal expansion, latent heat, and pressure effects on boiling.Warming widens atomic vibrations, expanding materials — hence rail expansion joints and bimetallic thermostats. Melting and boiling absorb latent heat at constant temperature, evaporation cools, ice floats because water expands on freezing, and pressurized geyser water superheats before flashing to steam.
10. The Laws of ThermodynamicsState the first and second laws of thermodynamics and Carnot's limit on engines.Energy is conserved (first law), but heat flows only from hot to cold and entropy tends to rise (second law). Carnot proved in 1824 that every heat engine must reject waste heat, capping efficiency by the hot and cold temperatures — the reason for cooling towers and the impossibility of perpetual motion.
11. Light Is an Electromagnetic WaveDescribe light as an electromagnetic wave and place visible light within the full spectrum.Maxwell showed light is a self-propagating electromagnetic wave traveling 299,792 km/s in vacuum. Radio, microwave, infrared, visible, ultraviolet, X-ray, and gamma radiation differ only in wavelength; eyes catch just the 380–700 nm sliver, while instruments like the VLA and X-ray machines read the rest.
12. Reflection and MirrorsApply the law of reflection and explain how curved mirrors form images and power telescopes.Light reflects at the angle it arrives, making smooth surfaces mirrors and rough ones diffusers; flat mirrors form virtual images. Concave mirrors focus parallel light to a point — from Newton's 1668 reflector to JWST's 18 gold-coated segments aligned to nanometers.
13. Refraction and LensesExplain refraction and how lenses — in magnifiers, eyes, and lighthouses — form images.Light bends when it changes speed at a boundary; shaped into a converging lens, it focuses images, as in a magnifying glass. The eye focuses with cornea plus adjustable lens (glasses correct its errors), and Fresnel's ringed lens design gave lighthouses powerful beams without impossible slabs of glass.
14. Where Color Comes FromTrace color to dispersion and scattering: prisms, rainbows, blue skies, red sunsets.Newton's prisms proved white light contains all colors, separated because glass bends short wavelengths more (dispersion). Raindrops disperse sunlight into 42-degree rainbows — doubled with a second internal reflection — while Rayleigh scattering by air molecules paints skies blue and sunsets red.
15. Interference, Diffraction, and PolarizationUse interference, thin films, and polarization to explain wave-only phenomena.Overlapping waves reinforce or cancel; Young's 1801 double-slit bands proved light's wave nature, and noise-canceling headphones apply the same idea to sound. Thin films (soap bubbles) and nanostructures (peacock feathers) color by interference, while polarizing filters block the oriented glare off horizontal surfaces.

Questions this course answers

Grounded in trusted sources

• OpenStax College Physics (Rice University) — waves, thermodynamics, and optics chapters
• James Prescott Joule, On the Mechanical Equivalent of Heat, Philosophical Transactions (1850)
• Sadi Carnot, Reflections on the Motive Power of Fire (1824)
• Isaac Newton, Opticks (1704)
• Thomas Young, Bakerian Lecture: On the Theory of Light and Colours (1801)
• NASA — Tour of the Electromagnetic Spectrum; James Webb Space Telescope documentation
• NIST — timekeeping and temperature standards
• NOAA — storm, ocean wave, and atmospheric optics resources

Every Wunder lesson is built from real, reputable sources — never invented.

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