Chapter 12 - Sound Flashcards
What is the speed of sound in air at 20º and 1 atm?
343 m/s
Define loudness.
Loudness is related to the intensity (energy per unit time crossing unit area) in the sound wave
Define pitch.
The pitch of a sound refers to whether it is high, like the sound of a piccolo or violin, or low, like the sound of a bass drum or string bass.
Describe sound waves.
We often describe a sound wave in terms of the vibration of the molecules of the medium in which it travels—that is, in terms of the motion or displacement of the molecules.
What is intensity defined as?
Intensity is defined
as the energy transported by a wave per unit time across a unit area perpendicular to
the energy flow
If a source is in the open so that sound can radiate out freely in all directions, the intensity decreases as ……
If a source is in the open so that sound can radiate out freely in all directions, the intensity decreases as the inverse square of the distance,
I ∝ 1 / r²,
What are nodes?
the standing waves have nodes (no movement) at the two ends, and one or more antinodes (large amplitude of vibration) in between. A node separates successive antinodes.
How does the diameter of a tube effect where the antinode will be in an open tube?
if the diameter is small compared to the length, which is the usual case, the antinode occurs very close to the end
Why is there always a displacement node most of the time at end of the closed end?
displacement node at the closed end (because the air is not free to
move) and an antinode at the open end (where the air can move freely).
Why is there a node at the end of an open tube in pressure variations in air?
Where the air in a wave is compressed, the pressure is higher, whereas in a wave expansion (or rarefaction), the pressure is less than normal. The open end of a tube is open to the atmosphere. Hence the pressure variation at an open end must be a node: the pressure does not alternate, but remains at the outside atmospheric pressure.
Why is there a node at the end of an closed tube in pressure variations in air?
If a tube has a closed end, the pressure at that closed end can readily alternate to be above or below atmospheric pressure. Hence there is a pressure antinode at a closed end of a tube
