Waves Flashcards
Travelling Mechanical Wave
a disturbance carrying energy through a medium without any overall motion of that medium
Travelling wave
either mechanical or electromagnetic, is a disturbance that travels out from the source producing it, transferring energy from the source to other places through which it passes
Transverse wave
where the direction of vibration is perpendicular to the direction in which the wave travels
Longitudal wave
where the direction of vibration is parallel to the direction in which the wave travels
Unit of Frequency
Hertz (Hz) where 1 Hz= 1 cycle per second 1s^-1
Reflection
The bouncing of waves off an obstacle in their path is called reflection of waves
Refraction
The changing of direction of a wave when it enters a region where its speed changes
Diffraction
The sideways spreading of waves into the region beyond a gap or around an obstacle
Interference
When waves from two sources meet a new wave is produced. The displacements that produced at any point by this wave is the algebraic sum of the displacements that each wave would produce on its own. This is called the interference of waves.
Constructive interference
when waves from two sources meet and the amplitude of the resulting wave is greater than the amplitudes of each of the individual waves, the waves are said to undergo constructive interference
Destructive interference
when waves from two sources meet and the amplitude of the resulting wave is less than the amplitudes of each of the individual waves, the waves are said to undergo destructive interference
coherant sources
two sources of periodic waves are said to be coherant if they are in phase or there is a constant phase difference between waves from each sources. If this is so the sources must also have the same frequncy
Interference pattern
when waves from two or more coherant sources meet the resulting wave pattern formed an interference pattern
stationary waves
when two periodic travelling waves of the same frequency and amplitude moving in opposite directions meet they interfere with each other. The resulting wave formed is called a stationary wave.
The Doppler Effect
The apparent change in the frequency of waves due to the motion of the source or the observer is called the doppler effect. If a source emits waves of frequency f, the observed frequency f’
greater than f = source moves towards observer
less than f= source moves away from observer
Doppler effect towards
f’=fc/(c-u)
Doppler effect away
f’=fc/ (c+u)
overtones
frequencies which are multiples of a certain frequency are called overtones of that frequency. If f is a given frequecy, 2f is the first overtone, 3f is the second overtone
Loudness
loudness of a sound wave dpends on the amplitude of the sound wave. The greater the amplitue the greater the loudness
Pitch
The pitch of a note depends n the frequency of the sound wave. The higher the frequecny, the higher the pitch, the lower the frequency the lower the pitch.
Quality
the quality of a musical note depends on the number of overtones present in the note and the relative sstrengths of the different overtones present
Frequency limits of audibility
The frequency limits of audibility are the highest and lowest frequencies audible by a human ear. The normal range is 20 Hz - 20 000 Hz
Resonance
If the frequency of a periodic force applied to a body is the same or very near to its natural frequency, that body will vibrate with very large amplitude. This phenomenon is called resonance
Sound Intensity at a point
is the rate at which sound energy is passing through unit area at right angles to the direction in which the sound is travelling at that point
Intensity =Power/Area
Units of sound intensity
watts per square metre (Wm^-2)
Threshold of hearing
The smallest sound intensity detectable by the average human ear at a frequency of 1000 Hz. Its value is 1 x 10^-12 Wm^-2
Sound intensity level
measured in decibels
Fundamental frequency of a string
a string vibrating with an antinode at its centre and a node at each end and no other nodes and antinodees is vibrating at its fundamental frequency.
Harmonics
frequencies which are multiples of a certain frequency f are called harmonics. f is the fundamental frequency or the first harmonic. 2f is the second harmonic. 3f is the third harmonic. etc.
The grating constant
the distance d between two adjacent slits (i.e. the width of one line and one slit) on the grating is called the grating constant or the grating spacing.
The fact that light can be polarised shows…
that light is a transverse wave
Dispersion
The separating out of the different wavelengths present in light is called dispersion
Primary colours
Red green and blue
Secondary colour
when two primary colours are mixed in equal intensity, the colour formed is a secondary colour e.g. yellow cyan and magenta
complementary colours
a primary colour and a secondary colour that when mixed give white are called complementary colours
