Notes
Wave properties
- Waves transfer energy, not matter. Mechanical waves need a medium; electromagnetic waves do not. Transverse waves move particles perpendicular to the wave; longitudinal waves move them parallel.
- Wave speed $v = f\lambda$; period $\displaystyle T = \frac{1}{f}$.
Sound
- Sound is a longitudinal mechanical wave. It is fastest in solids, slower in liquids, slowest in gases (about 343 m/s in air). Pitch depends on frequency and loudness on amplitude.
Light and the EM spectrum
- Order: radio, microwave, infrared, visible, ultraviolet, X-ray, gamma. Higher frequency means shorter wavelength. $c = f\lambda$, with $c = 3.0 \times 10^8 \text{ m/s}$.
- Reflection: angle of incidence equals angle of reflection. Refraction: bending as speed changes in a new medium. Convex lenses converge light.
Topics in this unit
Each topic has its own short notes and practice.
Practice
$v = f\lambda = 20 \times 0.5 = 10$ m/s.
Sound is a mechanical wave and needs matter.
The spectrum order of increasing frequency is radio, microwave, infrared, visible, UV, X-ray, gamma.
$\displaystyle \lambda = \frac{c}{f} = \frac{3.0 \times 10^8}{1.0 \times 10^8} = 3$ m.
Angle of reflection equals angle of incidence.
Light changes speed and bends at the water surface.
Free response
Write your answer first, then open the scoring guide.
Free-response question
A sound wave in air has a frequency of 170 Hz and travels at 340 m/s.
(a) Calculate the wavelength of the sound.
Show the answer and scoring guide
$\displaystyle \lambda = \frac{v}{f} = \frac{340}{170} = 2$ m.
Check off the points you earned:
(b) A student shouts toward a cliff and hears the echo 3 s later. How far away is the cliff?
Show the answer and scoring guide
The sound travels there and back: $\displaystyle d = \frac{vt}{2} = \frac{340 \times 3}{2} = 510$ m.
Check off the points you earned:
(c) If the frequency of the sound is increased, what happens to its pitch? Identify whether sound is transverse or longitudinal.
Show the answer and scoring guide
The pitch becomes higher. Sound is a longitudinal wave.
Check off the points you earned: