Waves Flashcards
What are progressive waves?
Wave which distribute energy from a point source to a surrounding area. They move energy in the form of vibrating particles or fields
What are mechanical waves?
Waves that are caused by a mechanical vibration or oscillation and require a medium to travel through such as air or water. These include sound waves, seismic waves and water waves
What are electromagnetic waves?
Waves that are caused by oscillations of electrons between different levels of energy and do not require a medium to propagate so they can travel through a vacuum. These include light waves, ultraviolet, infrared, radio waves, x-rays and microwaves
What are transverse waves?
Waves in which the direction of oscillation is perpendicular to the direction of travel. These include electromagnetic waves, some seismic waves (S type), water waves
What are longitudinal waves?
Waves in which the direction of oscillation is parallel to the direction of travel. These include sound waves, some seismic waves (P type)
What is the amplitude of a wave?
The maximum distance moved by a particle from its undisturbed position (halfway between the peak and the trough)
What is the wavelength of a wave?
The distance between successive peaks, or troughs, or any similar points on the wave
What is a complete cycle of oscillation?
The movement followed by a particle due to one wave
What is the frequency of a wave?
The number of complete cycles of oscillation that occur per second. Measured in Hz (1 Hz = 1 cycle per second)
What is the period of a wave?
The length of time taken for 1 complete cycle of oscillation
What equation links frequency and period?
T = 1/f
What is wave speed?
The wave speed is the speed of progression of the wave. It is the distance moved by a crest or any point on the waveform in one second
What is the phase of a wave?
The phase difference between 2 points n a wave is the fraction of a cycle by which one moves behind the other (expressed in degrees or radians)
Waves that are in phase are moving in the same direction at the same speed but are separated by a whole number of wavelengths.
Points that are separated by an odd number of half wavelengths are out of phase and waves that are out of phase by 180° are in antiphase
What is a wavefront?
A line joining all points of a wave that are in phase. The minimum distance between 2 points on a wave that oscillate in phase is equal to the wavelength. Wavefront is always perpendicular to wave direction
Reflection in light
The image and the object are equal distances from the mirror, the image is laterally inverted and the image is virtual/imaginary as no light is coming from it
Refraction in light
When light passes into another transparent material that is more optically dense then it slows down, causing it to bend towards the normal. The more dense the material, the more it slows
Refractive index
n = sin(i) / sin (r) = c vacuum / c material = λ vacuum / λ material
Refractive index is always greater than 1 and if light is travelling from material to vacuum then the equation must be inverted
Air can be treated as a vacuum
Diffraction
A wave will diffract as it goes through a gap or past an obstacle. Wavelength is unchanged before and after passing through the gaps. The closer the gap width is to the wavelength the more the wave will diffract
What is interference?
When 2 waves meet/cross they interfere and combine to give a resultant wave of a different amplitude. The pattern produced by the crossing of waves is called an interference pattern.
What is the principle of superposition?
The displacement of the point where the waves meet is equal to the vector sum of the displacements of each of the waves at that point
What is needed to form a ‘stable’ interference pattern?
They must be of the same frequency otherwise the interference pattern will be constantly changing
What is coherence?
Coherent waves are one with a constant phase difference (but do not have to be in phase) and will have the same frequency and wavelength. They are usually produced by the same source
What is destructive interference?
If 2 waves of the same type and frequency coincide so that a crest crosses a trough then the amplitudes completely cancel out. This is destructive interference and there will be no waves if the amplitudes are the same. This is a minima in light.
What is constructive interference?
If 2 waves of the same type and frequency combine so that 2 crests or 2 troughs coincide then there is constructive interference and the resultant amplitude is the sum of the separate amplitudes, and if the 2 initial amplitudes are equal then the amplitude of the resultant wave is double that of the original wave. This is a maxima in light.