Chapter 11 - Waves 1 Flashcards
What is a wave?
A physical phenomenon that transfers energy through a medium without transferring matter.
What are the two types of waves? (Direction)
Transverse (direction energy transfer perpendicular to direction of oscillation)
Longitudinal (direction of energy transfer parallel to direction of oscillation)
Wave equation
C = f x λ
Wave speed = frequency x wavelength
Phase of a particle/point
Fraction of a complete cycle/wave that a particle/point is at (at any given moment)
Phase difference
Difference in phase between two points along the same wave or between two waves at any given moment
Wave lengths in radians
1 complete wave = 2π
1/2 a wave = 1π
Phase formula and phase difference formula
Phase: (fraction of wave completed) x (2π)
Phase difference: (distance as fraction of wave) x (2π)
Phase difference = (phase in wave 1) - (phase in wave 2)
what is reflection
when a wave reverses direction upon meeting the boundary between two different media.
Angle of incidence = angle of reflection (i = r)
what is refraction
when a wave changes direction upon crossing the boundary between two different media
Wave properties in a medium (3 properties)
Speed through a medium is constant
Therefore the higher the frequency, the shorter the wavelength
Wave properties when passing through two media (3 properties)
Speed is fundamental property that changes when crossing between media
This leads to change in wavelength
Frequency remains constant
refraction rules
sound waves speed up going into physically denser mediums
EM waves slow down going into optically denser mediums
what is diffraction
phenomenon of waves spreading out when passing through a gap, or around an obstacle
diffraction rules
the smaller the gap relative to wavelength of wave, the greater the diffraction
gap size has to be similar/same order of magnitude as wavelength for significant diffraction to occur
wave speed and wavelength don’t change upon diffraction
what is polarisation
property of transverse waves which defines the plane of oscillation of the wave
EM wave polarisation
Plane of polarisation of an EM wave is defined as the plane in which the electric field vibrates.
what happens when a wave passes through a polarising filter?
the light passing through becomes polarised in one particular plane.
the intensity drops to half
what happens when polarised wave passes through another polarising filter
if polarised wave matches the plane of alignment, 100% of wave is transmitted
if polarised wave meets plane of alignment at some angle, less than 100% of the wave is transmitted
if polarised wave meets the plane of alignment at 90 degrees, 0% of the wave is transmitted
polarising light with reflection
light reflected off surfaces like metal and water is mostly polarised in the horizontal plane
sunglasses have vertically aligned polaroid filters to block all horizontally plane polarised light from reaching the eye (reducing glare)
intensity formulae
I = P/A
I = P/(4πr^2)
intensity relation to amplitude
intensity is proportional to amplitude squared
Τhe Electromagnetic Spectrum
Radio, Micro, Infrared, Visible, Ultraviolet, X-rays, Gamma
Radio waves = lowest frequency, longest λ, least energetic
Gamma waves = highest frequency, shortest λ, most energetic
All EM waves have same speed in vacuum. In other media, the speed varies.
refractive index formula
n = c/v
n is refractive index of a particular medium
c is speed of light in a vacuum
v is speed of light in that medium
refractive index relation with angles of incidence and refraction
(when light is incident in a vacuum and refracts into a medium of refractive index)
n = sin i / sin r
refractive index relation with angles of incidence and refraction
(when light is incident in a medium of refractive index and refracts into a vacuum)
1/n = sin i / sin r
when light goes from one medium to another medium
(neither of which is a vacuum)
n1sin(θ1) = n2sin(θ2)
total internal reflection, definition and conditions
phenomenon by which light completely reflects back at a boundary between two media, as opposed to transmitting across the boundary and refracting
- medium within which light is incident has a larger refractive index than second medium.
- angle of incidence exceeds the critical angle, for given medium
at the critical angle, the angle of refraction is 90 degrees… ray travels along boundary.
result of angle of incidence (relative to critical angle)
θ < C: refraction and partial reflection occurs
θ = C: light refracts along the boundary between two media
θ > C: total internal reflection
critical angle formula
sin(θc) = n2/n1
n2 = refractive index of second medium
n1 = refractive index of first medium
θc = critical angle
when at boundary between air/ vacuum:
sin(θc) = 1/n
