Sound and waves Flashcards
Define transverse wave.
The direction in which the energy travels is perpendicular to the direction of vibration of the particles of the medium.
Define longitudinal wave.
The direction in which the energy travels is parallel to the direction of vibration of the particles of the medium.
Define wavelength.
The distance between two successive compressions.
Can transverse or longitudinal waves be polarised?
Transverse waves can, longitudinal waves cannot be.
When a vibrating tuning fork touches a table top why does the sound appear louder?
As the table top is forced to vibrate at the same frequency as the tuning fork.
Define diffraction.
The spreading of a wave front into the geometrical shadow when it passes through a gap or around an obstacle.
Explain pitch.
Pitch is related to the frequency of a sound. The higher the frequency the higher the pitch.
Explain loudness.
The loudness of a sound depends on the amplitude of the vibration of the sound wave.
What are the characteristics of sound? (Three ways in which sound differ)
- Pitch
- Quality
- Loudness
Explain quality.
Depends on the number and intensity of the harmonics (overtones) present.
What are the two classifications of waves?
- Mechanical waves
- Electromagnetic waves
When is the diffraction more noticeable?
When the size of the gap or obstacle os approximately equal to or less than the wavelength of the wave.
What is used to demonstrate diffraction of light waves?
A diffraction grating.
Do sound waves have difficulty diffracting?
No they easily diffract.
Define interference.
Will occur when waves from coherent sources meet and combine.
Constructive interference gives a wave of great amplitude.
Destructive interference give a wave of smaller amplitude.
What is the condition for constructive interference?
When the waves meet they are in phase and the waves have the same frequency. The crest of one wave meets the crest of the other wave.
Explain coherent sources.
Coherent sources emit waves of the same frequency and the waves are in phase or have a constant phase difference.
What is the condition for destructive interference?
When the waves meet they are out of phase with a path difference of λ/2 or a multiple of this. The crest of one wave meets the trough of the other wave.
When are waves ‘in phase’?
When they are doing the same thing.
What is the wavelength of the stationary wave?
Twice the distance between successive nodes or successive antinodes.
Define the doppler effect.
The apparent change in the frequency of a wave due to the relative motion between source and observer.
Give two uses of the Doppler effect.
- Blood flow measurement
- Checking the heart beat of a foetus.
Explain natural frequency.
When a system that is capable of vibrating is made to vibrate it will do so at its natural frequency.
Explain forced frequency.
When an external vibration force acts on a system that is capable of vibrating the external force provides the forced frequency.
