Chapter 6 - Wave Behaviour Flashcards
Explain superposition.
When two or more waves meet, their displacements can be added together at every point. The principle of superposition states that when two or more waves overlap, the resultant displacement a given instance and position is equal the sum of the individual displacements that instance and position.
What is wavelength on a displacement - displacement diagram?
The distance between any two points at the same part of the wave cycle.
What is amplitude?
Maximum displacement of a wave from the equilibrium position.
What is time period?
The time it takes to return to the same position in the wave cycle moving in the same direction.
What is the equation for time period?
1 / f
What is phase?
The stage in a wave cycle. When two points are at the same stage in a cycle they are in phase.
What is phase difference?
The difference of points on a wave cycle, or the difference of phase of two waves at same point.
What does in phase mean?
When two waves are doing the same thing at the same moment - no phase difference.
What does in anti phase mean?
When two waves are doing exactly opposite things at the same moment - 180 degrees phase difference.
What does out of phase mean?
When waves are neither in phase or anti phase.
What is a phase angle?
Phase difference expressed in terms of 2pi radians or of 360 degrees. e.g. two waves which are half a cycle apart have a phase difference of pi or 180 degrees.
What is a phasor?
Phasors are used to represent amplitude and phase in a wave. A phasor is a rotating arrow used to represent a sinusoidally changing quantity.
What is the equation for phase angle (theta)?
2pif*t
What is the equation for phase displacement? (a is radius)
a sin (2pif*t)
What is a standing wave / stationary wave?
When two progressive waves of same frequency travel in opposite directions, the waves appear to stop moving. the nodes and antinodes appear to stay in the same place.
What is an antinode?
A point on a wave where there is maximum amplitude.
What is a node?
A point on a wave where there is zero amplitude.
How far is the distance between adjacent nodes?
Half a wavelength.
What is the equation for wavelength?
Wavelength (m) = wave velocity (m s^-1) / frequency (Hz)
Describe nodes and antinodes in closed end tube and give an example.
There is a node at the closed end and an antinode at the open end. e.g. clarinet
Describe nodes and antinodes in opened end tube and give an example.
There are antinodes at both ends e.g. flute
What is refraction?
the fact or phenomenon of light, radio waves, etc. being deflected in passing obliquely through the interface between one medium and another or through a medium of varying density.
What is the refractive index?
A ratio of the speed of light in one medium to the speed of light in another medium.
What is the equation for the refractive index of a material? (absolute refractive index)
speed of light in a vacuum / speed of light in material
What is Snell’s Law?
The ratio sin i / sin r is th refractive index of the material.
What is the normal?
A line drawn at 90 degrees to the surface of a transparent material.
Which way does the light bend if the ray goes from a less dense medium to more dense medium?
Towards the normal.
When is interference produced?
If two coherent waves overlap or if waves from a single source are divided and then reunited.
What is path difference?
The difference in distance travelled by two or more waves from one point to another.
When will waves meet in phase?
When their path difference = n*wavelength, when n is an integer.
When will waves meet in anti phase?
When their path difference = (n + 1/2) * wavelength, when n is an integer.
When are waves coherent?
When they have a clear constant phase difference. (Don’t have to be in phase)
Describe constructive interference.
It occurs when waves meet in phase leading to a larger superposition amplitude (a maximum).
Describe destructive interference.
It occurs when waves meet in anti phase leading to a lower superposition amplitude (a minimum)
What is diffraction?
The spreading of waves after passing through a gap or past the edge of an obstacle. The spreading increases as the gap becomes narrower.
What three things does diffraction not affect?
Wavelength, speed or frequency.
Describe Young’s double slit experiment.
Where light is shone through two slits of distance d apart, onto a screen. Bright and dark fringes of light can be observed on a screen that the light is shone onto. Bright fringes occur where the two light paths meet in phase. Dark fringes occur when the two light paths meet in anti antiphase.
What is the equation for path difference?
n * lamda = d sin(theta)
What is the equation for wavelength in terms of slit separation (d), bright fringe spacing (x) and slit - screen distance (L)?
Lamda = xd / L
What is the equation for line separation in metres of a diffraction grating?
1 / no. of lines per metre
What is the equation for wavelength in single slit diffraction?
lamda = b sin(theta)
If phasors make a complete circle what is the resultant phasor?
Zero.
