Sound Basics
A longitudinal mechanical wave produced by vibrating objects.
What is sound?
The relationship that connects wave speed, frequency, and wavelength. (hint: its a formula)
What is v=fλ?
Change in observed frequency when the source or observer is moving.
What is the Doppler effect?
The full range of electromagnetic waves ordered by wavelength or frequency.
What is the electromagnetic spectrum?
You look at a fluorescent bulb through a spectroscope and see discrete colored lines.
What is an emission spectrum (or line spectrum)?
Region of low density in a sound wave.
What is a rarefaction?
A sound has a frequency of 500 Hz and a wavelength of 0.68 m. What is its speed?
What is 340 m/s?
An ambulance approaches you. The pitch you hear is higher than the actual pitch.
What is the Doppler effect (waves are compressed)?
All electromagnetic waves travel at this speed in a vacuum.
What is the speed of light (c ≈ 3.00 × 10⁸ m/s)?
A radio wave has a wavelength of 3 m. What is its frequency? (c = 3.00 × 10⁸ m/s)
What is 1.00 × 10⁸ Hz (100 MHz)?
How high or low a sound is perceived. Related to frequency.
What is pitch?
In air at room temperature, the speed of sound is approximately this value.
What is 340–343 m/s?
A system vibrates strongly when driven at its natural frequency.
What is resonance?
The small band of the spectrum that human eyes can detect.
What is visible light?
Why are gamma rays dangerous?
What is they have enough energy to ionize atoms and damage living tissue?
Cycles per second. Unit is the hertz.
What is frequency?
Why does sound travel faster in steel than in air?
What is the material is stiffer and denser (or solids transmit sound faster than gases)?
The wavering loudness heard when two close frequencies interfere.
What are beats?
Highest energy, shortest wavelength electromagnetic radiation. Can ionize atoms.
What are gamma rays?
In the Speed of Sound Lab you find a resonant length of 0.25 m for a 340 Hz tuning fork in a closed tube. Estimate the speed.
What is about 340 m/s?
(For the fundamental, λ ≈ 4L = 1 m; v = fλ ≈ 340 m/s)
You stretch a physics slinky and push one end. A compression travels to the other end.
What is a demonstration that sound is a longitudinal wave?
You hear an echo 2.0 s after clapping. How far away is the reflecting wall? (Use v=340 m/s.)
What is 340 m?
(d=vt/2=340×2/2)
How are grandfather clocks tuned to be so precise?
What is the pendulum’s period is adjusted to match the desired tick (resonance / natural frequency)?
Maxwell predicted these while assembling his equations. A changing electric field produces a changing magnetic field (and vice versa).
What are electromagnetic waves?
Two tuning forks of 440 Hz and 444 Hz are struck together. How many beats do you hear per second?
What is 4 beats per second?
(fbeat=∣f1−f2∣f_\t)