11 - Waves Flashcards
What do waves transfer?
energy and information
How can you class waves?
mechanical or electromagnetic
Define a progressive wave
A wave that transfers energy from one place to another without a transfer of matter between the two points. The two progressive wave types are longitudinal and transverse waves.
What waves require a medium to travel through?
Mechanical waves require a medium, longitudinal waves require a medium and so can’t travel in vacuums.
What is a transverse wave?
A wave where the direction of oscillation is perpendicular to the direction of energy transfer of the wave. They have peaks and troughs at maximum displacement from the equilibrium position
Example of transverse waves
light waves, springs (slinkys), s waves, water waves, waves on a string
What is a longitudinal wave?
A wave where the direction of oscillation is parallel to the direction of energy transfer of the wave
Examples of longitudinal wave
sound waves, p waves
What is wave displacement?
distance from equilibrium position in metres
What is amplitude?
maximum displacement from equilibrium position in metres
What is wavelength?
length of one complete oscillation (distance between two same points of a wave)
What is time period?
the time taken for one full oscillation to happen in seconds
What is frequency?
the number of wavelengths that pass a certain point in one second measured in Hz
What is wavespeed?
The distance travelled by a wave per unit time measured in m/s
time period, freq equation
P=1/T
What is a wave profile?
A graph showing the displacement of particles in the wave against the distance along the wave. It can be used to determine the wavelength and amplitude of both types of wave. The displacement of the particles in the wave is continuously changing so the wave profile changes shape over time
What can be determined from a wave’s displacement against time graph?
time period and amplitude of both types of wave
Wavespeed equation
v=fλ
velocity = frequency x wavelength
What is phase difference?
the difference between the displacement of the particles along a wave or the difference between the displacements of the particles on different waves.
What is phase difference measured in?
degrees or radians (2pi radians = 360degrees)
Phase difference equation
Ф= (x/λ) x 360°
Ф= (x/λ) x 2pi
What is a wavefront?
a line joining points on a wave, which are in phase
When does reflection occur?
When a wave changes direction at a boundary between two different mediums, remaining in the original medium, e.g. a mirrored surface.
What is the law of reflection?
The angle of incidence is equal to the angle of reflection when measured to the normal
Change in wave properties during reflection
frequency and wavelength of wave remain unchanged
When does refraction occur?
When a wave changes direction as it changes speed when it passes from one medium to another. The amount of refraction depends on the refractive index of the material
Change in wave properties during refraction
wavelength changes but frequency remains unchanged
Refraction - entering medium with higher optical density
Wave slows down, wavelength decreases, bends towards normal
Refraction - entering medium with lower optical density
wave speeds up, wavelength increases, bends away from normal
What is the refractive index equal to?
the speed of light in vacuum / the speed of light in material
or sini/sinr
greater refractive index…
the more the light entering the medium is refracted towards the normal
refractive index (n) equation
n=c/v
refractive index = 3x10^8 / speed in medium
What is diffraction?
The spreading out of a wave as it passes through a gap/aperture or when it encounters an obstacle
Change in wave properties in diffraction?
speed, wavelength and frequency remain unchanged
Conditions for diffraction
Diffraction will only occur if the wavelength of the wave is of a similar size to the size of aperture. Diffraction effects are more significant when the wavelength is a similar size to the gap
What is polarisation?
The particles oscillate along one direction only, confined to a single plane
polarised v unpolarised light
Unpolarised light is light which oscillates in many different planes wheres polarised light is light which oscillates in one plane only
Why can’t longitudinal waves be polarised?
The direction of oscillations are already in the same direction that the wave travels in (already acts on single plane) so only transverse waves can be polarised
What is total internal reflection?
When all light is reflected back into the original medium and no refraction occurs
Conditions for TIR
original material must have higher refractive index than surrounding material (e.g. glass to air), angle of incidence must be greater than the critical angle
What is the critical angle?
The critical angle is the angle of incidence above which the total internal reflection occurs, the angle of incidence where the angle of refraction is 90°
critical angle equation
sinc =1/n
TIR equation
n1sinϑ1=n2sinϑ2
