Waves, Light, and the Electromagnetic Spectrum
Core vocabulary and ideas about wave anatomy, mechanical vs electromagnetic waves, and the unified EM spectrum.
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Questions Covered in This Set
10 cards to master
What actually travels in a wave?
A pattern of disturbance carrying energy and information — not the matter itself. A leaf on a pond bobs up and down while the ripple moves outward.
Define wavelength (λ) and frequency (f).
Wavelength is the distance from one crest to the next (metres). Frequency is how many crests pass a fixed point per second (hertz).
State the wave equation and what it implies.
v = fλ. Since speed is fixed by the medium, frequency and wavelength trade off inversely: higher frequency means shorter wavelength.
What does amplitude control, and how does it relate to energy?
Amplitude is the size of the disturbance — loudness for sound, brightness for light. Energy scales with amplitude squared, so doubling amplitude quadruples power.
Why do bass notes travel through walls and around corners better than treble?
Low frequency means long wavelength (40 Hz ≈ 8.6 m), and waves bend around obstacles comparable to or smaller than their wavelength.
Mechanical wave vs electromagnetic wave?
Mechanical waves (sound) need a medium to travel through; electromagnetic waves (light) need no medium and travel through vacuum at c ≈ 3 × 10⁸ m/s.
Longitudinal vs transverse waves — give an example of each.
Longitudinal: the medium jiggles along the direction of travel (sound, a pushed Slinky). Transverse: the medium moves perpendicular to travel (water waves, guitar strings).
What did Maxwell discover in the 1860s?
That a changing electric field creates a magnetic field and vice versa, so the two bootstrap each other through empty space — at exactly the measured speed of light. Light IS an electromagnetic wave.
Why do radio, visible light, and X-rays have different names?
Historical accident — different discoverers with different instruments. They are the same phenomenon, differing only in wavelength/frequency.
Order the EM spectrum from longest to shortest wavelength.
Radio → microwave → infrared → visible → ultraviolet → X-ray → gamma ray.
