Waves Flashcards
Displacement (m)
The distance any part of the wave has moved from its mean (rest) position. It can be negative or positive.
Amplitude (m)
The maximum displacement, it is always positive.
Wavelength
The distance the wave travels before repeating itself.
Period
The time to complete one oscillation.
Phase difference
The difference, in radians, between two points that have the same pattern of oscillation.
Frequency (Hz)
The number of oscillations per unit time at any point, the reciprocal of Period.
Speed of a Wave (ms-1)
The waves distance over time. For one Period that would be one wavelength.
Stationary or Standing Wave
The wave is not progressive, its peaks and troughs are not moving forward but oscillating in place, so no net transfer of energy. Forms a pattern of Nodes & Antinodes.
Nodes (N for “not moving” or “no displacement)
Points in a stationary wave at which there is no displacement at any time.
Antinodes (A for maximum Amplitude)
Points in a stationary wave where the displacement varies by the maximum amount.
Reflection
The change in direction of a wave at an interface between two different media so that the wave returns into the medium from which it originated.
Refraction
The change of direction of a wave that occurs when its speed changes due to a change in medium. velocity/wavelength change, frequency does not
Total Internal Reflection
When all of the wave is reflected and there is therefore no refraction. It occurs when the angle of incidence > critical angle. Angles ALL measured from Normal to the surface.
Critical Angle
The angle of incidence in a denser medium for which the angle of refraction is 90o
sin (C) = 1 / µ where µ is the refractive index and C the critical angle.
Diffraction
Happens when a wave encounters an object or a slit and deviates from its path. The effect is more pronounced for wavelengths roughly comparable to the dimensions of the object or slit.
Interference
Occurs when two or more waves overlap and superpose to form a resultant wave where the waves reinforce each other in places and cancel each other in others.
Fundamental mode of vibration
The simplest stationary wave where the length is half the wavelength of the wave.
Harmonics
A simple multiple of the fundamental frequency.
Wavefront
The point on a ripple of a wave that is at the same phase.
Coherance
Coherent= constant phase difference (0 or other) between waves.
Path difference
The distance from the slit to the point where the waves interfere.
Superposition
When two or more waves meet, the total displacement at any point is the sum of the displacements that each individual wave would cause at that point. Note displacement is a vector so direction is important.
(Plane) Polarised Wave (applies only to Transverse waves)
Oscillations occur in only one plane or direction, and (as transverse) perpendicular to the direction of travel or propagation.
Unpolarised Wave (applies only to Transverse waves)
Oscillations occur in many planes or directions, and (as transverse) perpendicular to the direction of travel or propagation.
Longitudinal Wave
Oscillation displacement is parallel to direction of wave or energy travel.
Transverse Wave
Oscillation displacement is perpendicular (90o) to direction of wave or energy travel.
