Physics waves flashcards

Wave

vibrations which repeat backwards and forwards motion (oscillations) which transfer energy without any transfer of matter

Transverse wave

oscillations are perpendicular to the direction of energy transfer

Longitudinal wave

oscillations are parallel to the direction of energy transfer

Wavespeed equation

v = fλ

• v - wave speed

• f - frequency

• λ - wave length

Phase equation

an angle to describe the position in a complete cycle oscillation

Displacement-distance graph features

• distance on x-axis

• displacement on y-axis

• seeing every point at ‘snapshot’

• The entire wave moving

Displacement-time graph features

• time on x-axis

• displacement on y-axis

• focused on one single point moving

• Longitudinal waves still represented as transverse wave, as the displacement is still plotted on y-axis

Frequency-time-period equation

T = 1 / f

Time period

Time for one complete oscillation

• measured in s

Frequency

Number of waves per second

• measured in Hertz (Hz)

‘Out of phase’

waves that are not at the same angle at the same point or there is a phase difference

angular separation

the phase difference between two waves / lines

anti-phase

the wave is like a ‘reflection’ of the other on the x-axis

Phase

the angular position of the wave

Coherence

 constant phase difference between two waves 

• Must have the same frequency

Principle of superposition

where two or more waves meet, the total displacement at any point is equal to the vector sum of the displacements of the individual waves 

Stationary / standing waves

a wave which the crests and troughs do not travel (i.e. they only move up and down)

• Only oscillates, does not propagate 

Superpose

when two waves interfere as they overlap

Constructive interference

when the wave displacements of the 2 waves are in the same direction as each other. 

• Taking the vector sum of displacements means that the resultant wave has a bigger displacement than the waves that created it

Destructive interference

when the wave displacements of the 2 waves are in the opposite direction to each other.

• Taking the vector sum of these displacements means that the resultant wave has a smaller displacement than the waves that created it.

Node

a point on a standing wave where the resultant displacement is zero (i.e. it is not vibrating)

• Waves always meet at opposite displacements at this point

• Node = no displacement

Anti-node

a point on a standing wave where the resultant displacement is maximum 

• waves always meet in phase at this point

First harmonic (fundamental frequency)

the lowest frequency which can be held 

• Length of wave = λ/2

Harmonic number

the number of antinodes

Number of nodes

harmonic number +1

Progressive wave

an oscillation that transfers energy and information from one location to another through a medium/vacuum

Standing wave setup procedure

• Progressive wave travels along string from vibration generator 

• Wave reflects and travels back along string when it reaches boundary (end of string)

• Fixed boundaries are nodes

• This causes two waves of the same wavelength, amplitude and frequency travelling in opposite directions

• The wave superpose/interfere

• At some point the two waves meet and always interfere destructively, causing a node and interfere constructively, causing an anti-node

First harmonic frequency equation

• T - Tension

• μ - mass per unit length

• l - length (from first to last node)

Coherent waves

when two different waves have a constant phase difference they are said to be coherent waves

• Lasers produce coherent waves

• They must have the same frequency and wavelength 

Path difference

extra difference travelled by one wave compared to another (coherent waves)

• Must be a whole number of wavelengths plus half a wavelength (or an odd multiple of half wavelengths) for the waves to meet in anti-phase

Fringe separation equation (Young’s double slit)

W = 𝜆D / s

• W - the fringe separation [m]

  • middle of one bright fringe to the middle of next bright fringe 

• 𝜆 - wavelength [m] 

  • Red - around 700 nm

• D - distance from slits to screen [m]

• s - slit separation [m]

  • Centre of one slit to centre of other