Waves - Level 3 Flashcards
Harmonic frequencies
Standing wave patterns are only created within a medium at specific frequencies of vibration. These frequencies are known as harmonic frequencies, (harmonics).
Fundamental frequency/first harmonic
The fundamental frequency/1st harmonic is the lowest possible frequency at which a string could vibrate to form a standing wave pattern (only 1 loop is formed).
Harmonics in a column with both ends open
The standing wave patterns will have anti-nodes at each end of the air column and a node in between.
λ = 2L f = v/λ
(>< shape)
Why are other frequencies produced when a whistle is blown?
The other frequencies produced are overtones (frequencies that are higher than the fundamental frequency of the vibration). When the whistle is blown, a mixture of overtones produces a distinctive sound (timbre). This causes different tones/beats to be produced between fundamental frequencies.
Beat frequency
A beat is an interference between two sound waves of slightly different frequencies. When two sound waves of slightly different frequencies approach your ear, the alternating constructive and destructive interference produces beats, causing the sound to be alternatively soft and loud. The rate of beats is the differencebetween the two frequencies.
Harmonics in a column with one end open, one end closed
The standing wave patterns will have a node at one end and an anti-node at the other end of the air column.
λ = 2L f = v/λ
(< shape)
- Only odd harmonics of the frequencies are produced
Harmonics in a column with both ends closed
The standing wave patterns will have nodes at each end of the air coluumn and an anti-node in between.
λ = 2L f = v/λ
(<> shape)
Calculate the frequency of any harmonic
- Calculate the frequency of the 1st harmonic
- Multiply the frequency value by the number of the harmonic you want to calculate
(f1 x 2 = f2)
Relationship between pulse speed, tension and linear density
The velocity of the wave depends on the linear density (µ) of and the tension (T) in the string. Making the string tighter and lighter increases the pulse speed, and making the string loser and heavier slows the pulse speed.
v = τµ
Interference
Interference is the combination of two or more waves to form a resultant wave.
Interference conditions for light /sound sources
- Light sources must be coherent, maintaining a constant phase relationship
- Light must be monochromatic, consisting of just one wavelength (λ)
Principle of superposition of waves
When two or more propagating waves of same
type are incident on the same point, the total displacement at that point is equal to thevector sumof
the displacements of the individual waves.
Constructive interference
Constructive interference is when acrestof a wave meets a crest of another wave, or a troughof a wave meets a trough of another wave, having the same
frequency at the same point. The total displacement of the waves is equal to the sum of the individual displacements.
Deconstructive interference
Deconstructive interference is when a crest of one wave meets a trough of another wave. The total
displacement of the waves is equal to the difference between the individual displacements.
Path difference and phase difference of interfering waves
(Antinodal lines - maximum points - constructive interference)
From the centre anti-nodal point onwards
Path difference - 0, 1λ, 2λ, 3λ…nλ
Phase difference - 0, 2π, 4π, 6π…