Sound and Waves Flashcards
What are mechanical waves?
-Need a medium to travel through
-Cannot travel through a vacuum
E.g. sound waves
What are electromagnetic waves?
-Don’t require a medium to travel through
-Travel at the speed of light
E.g. Visible light
Define Transverse Waves?
Waves in which the direction in which the energy travels is perpendicular to the direction of vibration of the particles of the medium.
Define longitudinal waves.
The direction in which the energy travels is parallel to the direction of vibration of the particles of the medium.
Difference between transverse and longitudinal waves.
Transverse waves can be polarised but longitudinal waves cannot be polarised.
Define wavelength.
The distance from one point on a cycle to the exact same point on the next cycle.
Define amplitude.
Maximum disturbance of any particle from its’ original position.
Define oscillation.
The disturbance produced by one complete cycle.
Define frequency.
The number of cycles passing any point in a second. 1 cycle per second is 1 Hertz.
Define velocity using distance and time. (in terms of waves)
The distance travelled by one cycle in one second.
Define diffraction.
Diffraction is the spreading out of a wave into the geometrical shadow when it passes through a gap or around an obstacle.
Define interference.
Interference is when waves from coherent sources overlap and a new wave is formed of greater or lower amplitude.
Define refraction.
Refraction is the bending of light as it passes from one medium to another medium of a different refractive index. The velocity of a wave changes as it travels through a medium of different refractive index.
Define the doppler effect.
The apparent change in frequency of waves due to the relative motion between the source and the observer.
Define threshold of hearing.
The threshold of hearing is the smallest sound intensity detectable by the average human ear at 1kHz
Define resonance.
Resonance is the transfer of energy between two bodies of the same natural frequency.
What are stationary waves and how are they produced?
Stationary waves are waves where there is no net transfer of energy.
Stationary waves are produced when two progressive waves of the same amplitude, same frequency, same speed and moving in opposite directions meet.
Define nodes and antinodes.
Nodes are points along the medium where the displacement is zero.
Antinodes are points along the medium where the displacement is a maximum.
Wavelength ratio for resonance for pipes closed at both end, open at one end at open at two opens
Closed at both-lambda/2
Closed at one end-lambda/4
Open at both-lambda/2
Define coherent sources
Coherent sources emit waves that have the same frequency, same waveform with a constant phase difference between them.
Define harmonics.
Harmonics are multiples of the fundamental mode of vibration.
What is the relationship for pitch, loudness, quality.
Pitch is related to the frequency of sound.
Loudness depends on the amplitude of vibration.
Quality depends on the number and intensity of the harmonics present
When does resonance occur?
When forced frequency equals natural frequency.
Define sound intensity. (Formula)
Sound intensity is the sound energy per second per unit area.
Sound intensity = sound energy per second / area energy passes through
Watts per metre squared = energy per second / area
Define constructive interference and destructive interference.
Constructive: When two waves combine to give a wave of greater amplitude.
Destructive: When two waves combine and cancel out.
What is the minimum phase difference for total destructive interference? What two other conditions are there?
lambda / 2;
Same amplitude
Waves from coherent sources
Give two applications of the Doppler Effect.
Police speed gun
To measure the velocity of stars.
Ultrasound
What is the relationship between the frequency of the first harmonic and the frequency of the second harmonic?
The second harmonic is double the frequency.
Give two formulas for the speed of sound experiment?
c = f x 4(l+0.3d)
c = f x 2{l2 - l1} (l1=length of pipe at first harmonic)
What does 3dB increase in sound intensity level represent in sound intensity?
Doubling sound intensity.
What scale is used to measure sound intensity levels? The human ear is more sensitive to specific frequencies how does this scale take this into account.
The Decibel Adapted Scale;
sound level meter responds more to sounds between 2kHz and 4kHz just like the ear.
What causes the red shift in the spectrum of a distant star? And blue shift?
Star moves relative to Earth. Longer wavelength moving away from Earth. (red)
Star moves relative to Earth. Shorter wavelength moving toward Earth. (blue)
What is a diffraction grating?
A diffraction grating consists of a number of very thin lines with transparent gaps between them which are as wide or very close to the wavelength of light.
What is the formula for calculating the distance between images on a screen?
DxTan(pieta) = x
D = distance to screen
x = distance between images
Why can sound not be polarised but light can?
Sound waves only travel in one direction (parallel to the vibration of their particles) but light can vibrate in more than one plane.
Explain why a dog whistle can be heard by a dog but not by a human.
Whistle is very high frequency, above frequency limits of audibility.
Explain why a dog whistle can be heard by a dog but not by a human.
Whistle is very high frequency, above frequency limits of audibility.
What does red-shift tell us about the universe?
The universe is expanding
What harmonics are produced by a pipe open at one end?
Only odd harmonics
Explain why a piece of music sounds different on different instruments.
A closed at one end pipe instrument emits odd multiples of the fundamental frequency.
An open at both ends pipe instrument emits all multiples of the fundamental frequency.
State two uses of microwaves.
Ovens.
Television Remote
What are the frequency limits to which humans can hear?
20-20,000Hz
