Longitudinal and Transverse Waves

What are progressive waves defined as?

#A wave that transfer energy from one point to another without transferring the medium itself

What is the displacement of a wave?

#The distance of a point on the wave from its equilibrium position

—> It is a vector quantity; it can be positive or negative

What is amplitude?

#the maximum displacement of a particle in the wave from its equilibrium position

What is wavelength?

#the distance between points on successive oscillations of the wave that are in phase

What are the units of wavelength?

#Metres(m)

What is Period(T) or time Period

#the time taken for one complete oscillation or cycle of the wave

What is the units of Time period?

#Seconds(s)

What is frequency(f)?

#the number of complete oscillations per unit time.

What are the units for frequency?

#Measured in Hertz (Hz) or s^-1

What is speed(v)?

the distance travelled by the wave per unit time

What are the units for speed?

• #Measured in metres per second (m s^-1)

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What is the equation linking speed, frequency and wavelength?

#(Wave speed/ speed of light) = frequency x wavelength

(v/c) = f x lambda

What happens to the frequency of a wave as the wavelength increases?

#As the wavelength increases, the frequency decreases

What happens to the frequency of a wave as the wavelength decreases?

#As the wavelength decreases, the frequency increases

What is Phase difference between two waves?

#a measure of how much a point or a wave is in front or behind another

What happens when crests or troughs are aligned?

#When the crests or troughs are aligned, the waves are in phase

What happens when crest of one wave aligns with the trough of another?

#When the crest of one wave aligns with the trough of another, they are in antiphase

What are the units of phase difference?

#Phase difference is measured in fractions of a wavelength, degrees or radians

How can phase difference be described?

• #

• In phase is 360^o or 2π radians

• In anti-phase is 180^o or π radians

How do particles oscillate in mechanical waves?

#In mechanical waves, particles oscillate about fixed points

What are the two types of waves?

• #

• Transverse waves

• Longitudinal waves

What are transverse waves?

#A wave in which the particles oscillate perpendicular to the direction of the wave travel (and energy transfer)

What are the examples of transverse waves?

• #

• Electromagnetic waves e.g. radio, visible light, UV

• Vibrations on a guitar string

• Waves on a string

• Seismic (S) waves

Where can transverse waves be shown?

#On a rope

What is a longitudinal wave defined as?

#A wave in which the particles oscillate parallel to the direction of the wave travel (and energy transfer)

What are the regions of transverse waves?

#Creasts and peaks

What are the regions of longitudinal waves?

#Compressions and rarefactions

What are compressions?

#Regions of increased pressure

What are rarefactions

#Regions of decreased pressure

What process can occur to transverse waves but not longitudinal waves?

#Polarisation

How can longitudinal waves be shown?

#On a slinky spring

What happens when energy is transmitted in a transverse wave?

#Energy is transmitted through the wave

• The particles in the medium vibrate as they are given energy

• The compressions cause the nearby particles to also vibrate with more energy

• This produces a compression further along in the medium

What are examples of longitudinal waves?

• #

• Sound waves

• Ultrasound waves

• Waves through a slinky coil

• Seismic (P) waves

What is polarisation?

#Event when Particle oscillations occur in a single plane perpendicular to the direction of wave propagation

What does it mean when a transverse wave is polarised?

#When transverse waves are polarised, this means:

• Vibrations are restricted to one direction

• These vibrations are still perpendicular to the direction of propagation / energy transfer

Why does polarisation only occur with transverse waves?

#Polarisation can only occur in transverse waves

• This is because transverse waves oscillate in any plane perpendicular to the propagation direction

What is the difference between unpolarised and polarised transverse waves?

#In unpolarised waves, there is oscillations of particles in any direction perpendicular to the direction propagation, whereas polarised waves only have oscillations perpendicular to direction of propagation in one direction

Why can’t longitudinal waves be polarised?

#Longitudinal waves (e.g. sound waves) cannot be polarised

• This is because they oscillate parallel to the direction of travel

How can waves be polarised?

#Waves can be polarised through a polariser or polarising filter

• This only allows oscillations in a certain plane to be transmitted

What are polaroid glasses?

#Glasses containing lens with polarising filters with transmission axes that are vertically oriented

• This means the glasses do not allow any horizontally polarised light to pass through

How do polaroid glasses work?

#

Polaroid sunglasses only transmit vertically polarised light

Horizontally polarised light is blocked

Vertically polarised light passes through

What happens when light is reflected from a reflective surface?

#When light is reflected from a reflective surface e.g. the surface of water or a wet road, it undergoes partial plane polarisation

• This means if the surface is horizontal, a proportion of the reflected light will oscillate more in the horizontal plane than in the vertical plane

Why are polaroid sunglasses useful at reducing glare?

#polaroid sunglasses are useful in reducing the glare on the surface of the water (or any reflective surface) as the partially-polarised light will be eliminated by the polarising filter

How are polaroids used in photography?

• #

• They are very useful for capturing intensified colour and reducing glare on particularly bright sunny days

• Polarising filters also enable photographers to take photos of objects underwater

Why are polaroids used in underwater cameras?

#This is because the light reflected on the surface of the water is partially polarised in the horizontal plane

• This glare is eliminated by the polarising lens

• However, the light from the underwater object is refracted by the surface of the water, not reflected, so it is not plane-polarised

• Therefore, the light from the underwater object is more intense than the glare and shows up much more brightly in the photo