Chapter 11 - Wave 1 Flashcards
What is a wave?
A wave is a method of transferring energy
What is the formula for amplitude?
(Crest - Trough)///2
What is the difference between P and S waves?
P waves are longitudinal, can only travel through solids
S waves are transverse, travel through solid and liquids
What is a progressive wave?
A progressive wave is an oscillation that travels through matter (in some cases, a vacuum). All progressive waves transfer energy from one place to another; particles in the matter vibrate, but they do not move along the wave
What does dampening/attenuating mean?
The medium a wave travels through can dampen/attenuate the wave, which means to take energy away
How do particles act in a progressive wave?
When a progressive wave travels through a medium, particles in the medium move from their original equilibrium position to a new position and back
What is the restoring force?
Particles In the medium exert forces on each other, a displaced particle experiences a restoring force to be pulled back to its original position by its neighbour particles
How can a waves speed be changed?
A wave remains at the same speed unless the density of the medium is changed
What are the oscillations of a transverse wave like?
Transverse waves oscillate perpendicular to the direction of energy transfer: the peaks and troughs are where oscillating particles are at maximum displacement from equilibrium position
What is a misconception about particles in transverse and longitudinal waves?
The particles do not move constantly forward, but oscillate around the same equilibrium position
What are oscillations in a longitudinal waves
Longitudinal waves oscillate parallel to the direction of energy transfer: the compressions and rarefactions are where oscillating particles are closest and furthest separate
What is the amplitude of a longitudinal wave?
The amplitude in the distance a particle moves back and forth divided by 2
What is the displacement of a wave?
The distance from the equilibrium position in a particular direction
What is the amplitude of a wave?
Maximum displacement form the equilibrium position
What is the wavelength of a wave?
Minimum distance between two of the same points in adjacent waves
What is the time period of oscillation?
The time take for one oscillation
The time taken for a wave to move one whole wavelength past a given point
What is frequency?
The number of wavelengths passing a given point per unit of time
What is wave speed?
The distance travelled by the wave per unit of time
V = Frequency *** Wavelength
What is the phase of a particle/point?
The phase of a particle/point is the fraction of a complete cycle/wave that a particle/point is at
What is the phase difference?
The phase difference is the difference in the phase between 2 points along the same wave between two waves at any given point in time
How long is one complete wave in radians and degrees?
360O
or
2pi Radians
What is the formula for a phase?
Phase === Fraction of Wave Completed *** 2pi
What is the formula for phase difference?
Phase difference === d/W *** 2pi
Where ‘d’ is the distance between two points and ‘W’ is wavelength
What does it mean if two waves are in phase?
The two waves line on each other so that the phase difference is an even multiple of pi
What does it mean if two waves are out of phase?
If two waves are out of phase, they lie slightly off each other so that the phase difference is somewhere between 0 and ‘n’pi
What does it mean if two waves are antiphase?
If two waves are antiphase, they lie completely off each other so that where they intersect, they move in completely different directions
This makes the phase difference an odd multiple of pi
When is phase difference constant?
When two waves of the same frequency meet at a point as time moves forward
When is phase difference changing?
When two waves of different frequencies meet at a point, as time moves forward
What are wavefronts?
Wavefronts are lines of constant phase so that a change in wavefronts illustrates a wave phenomenon
What is diffraction?
Diffraction is where waves pass through a gap and spread out; this is a unique property of waves
What is reflection?
Reflection is when a wave reverses direction upon meeting the boundary between two different mediums
What is the law of reflection?
The law of reflection is the angle of incidence ‘I’ is equal to the angle of reflection ‘R’
What is refraction?
Refraction is when a wave changes speed and/or direction upon crossing the boundary between two different mediums
What changes when a wave refracts?
If a wave is refracted, the speed always changes. This leads to a change in wavelength as frequency is constant
Direction only changes if the angle of incidence is not 0
What does the distance between wavefronts mean?
When wavefronts are closer, they are travelling slower, as more wavelengths have to go pass to travel the same distance
What does the relationship between the angle of refraction to the angle of incidence?
When n > 1, R < I
When n < 1, R > I
What happens to a wave when it slows down during refraction?
When a wave slows down, it bends towards the normal and wavelength gets shorter
What happens to a wave when it speeds up during refraction?
When a wave speeds up, it bends away from the normal and wavelength gets longer
What is the relationship between physical density and speed?
The greater the physical density of a medium, the faster the mechanical wave or sound wave
What is the relationship between optical density and speed?
The greater the optical density of a medium, the slower the EM wave
What affects the amount of diffraction occur?
The narrower the gap, the greater the diffraction
The longer the wavelength, the more the greater the diffraction
What do not change upon diffraction?
Wavespeed
Wavelength
Frequency
Only direction changes
What has to be the case between wavelength and gap size for diffraction to occur?
Gap size has to be of a similar magnitude to wavelength
The smaller the gap compared to wavelength the greater the diffraction
What waves experience polarisation?
Transverse Waves
What is the plane of polarisation?
The plane of polarisation of an EM wave is defined as a plane of which the electrical field vibrates
What types of waves are most sources of light?
Unpolarised EM waves
What does unpolarised waves mean?
Unpolarised means it consists of different waves that have their electrical field aligned in different planes
What are the 2 ways EM waves are polarised?
Absorption (Polaroid Filters)
Reflection (Sunglasses)
What is the plane of alignment?
The plane of alignment of a polaroid filter is the plane which it will allow electrical field oscillations to pass
What does a polarisation filter allow through?
The filter allows the e-fields aligned in the same plane as alignment, as well as components of all other waves in the same plane as alignment
What does it mean if the plane of polarisation matches the plane of alignment?
100% of the wave is transmitted, and it loses half the intensity
What does it mean if the plane of polarisation is at some angle to the plane of alignment?
< 100% of the wave is transmitted
Intensity is directly proportional to cos2x
What does it mean if the plane of polarisation is perpendicular to the plane of alignment?
0% of the wave is transmitted
What happens to light reflected off metal and water?
Light waves are mostly polarised in the horizontal plane
How do sunglasses filter light?
Sunglasses have vertical polaroid filters to block horizontal polarised light
What is the definition of intensity?
Intensity is defined as power per unit area
What is the formula for intensity?
Intensity = Power (W) /// Cross-A (m2)
What is the formula for intensity with a given distance?
Intensity = Power /// 4pi(r2)
What is the relationship between distance and intensity?
Intensity is inversely proportional to the radius squared
What is the relationship between amplitude and intensity?
Intensity is directly proportional (Amplitude)2
How can EM waves be made?
A changing current in a wire creates waves of changing electric and magnetic fields that radiate from the wire (EM waves)
What are the properties of EM waves?
EM waves are transverse in nature and the electrical fields are in phase and perpendicular to the magnetic fields
What is the wavelength of red?
700nm
What is the wavelength of purple?
400nm
What is the relationship between frequency, wavelength, and energy?
The higher the frequency, the lower the wavelength, and the higher energy per photon
How can EM waves be affected?
EM waves can be reflected, refracted, diffracted, and superposed
Through which medium do all EM waves travel at the same speed?
All EM waves travel through at the same speed only through a vacuum
What are the uses of EM polarisation?
The polarisation of EM waves is communication transmitters in order to reduce interference between different transmitters
What is the refractive index?
The refractive index of a medium is a ratio between of the speed of light in a vacuum to the speed of light in that medium
What is the formula for the refractive index?
n = c / v
n = Refractive Index
c = 3x108
v = Speed of light in that medium
What is the relationship between refractive index, refraction, and change in speed?
The greater the refractive index, the greater the decrease in speed, and the more light refracts
What is the wavelength formula for refractive index?
n = yc / yv
c = Wavelength in vacuum
v = Wavelength in medium
What is the formula for refractive index using the incidence and refractive angle?
n = sin i / sin r
‘I’ is the angle of incidence
‘r’ is the angle or refraction
What is the formula linking light between 2 mediums of different refractive indices?
n1sin(x1) = n2sin(x2)
What is total internal reflection?
Total internal reflection is a wave phenomenon by which light completely reflects back at a boundary between 2 media
What are the conditions for total internal reflection?
Medium within light is incident has a larger refractive index than the second medium
Angle of incidence exceeds the critical angle for a given medium
What happens when the angle of incidence is less than the critical angle?
Refraction and partial reflection occurs
What happens when the angle of incidence is equal to the critical angle?
Light refracts along the boundary between the 2 medium
What happens when happens when the angle of incidence is greater than the critical angle?
Total internal reflection
What is the formula for the critical angle?
sin xc = n2 / n1
n2 = Refractive index of second medium
n1 = Refractive index of incidence medium
xc = Critical angle
How does n1sin(x1) = n2sin(x2) relate to the calculation of the critical angle?
The incidence angle is the critical angle and the refractive angle is 90o as the ray moves across the wave boundary
What are the wavelengths of EM waves in order from greatest to smallest?
Radiowaves: 10cm to 1km
Microwaves and IR: 1mm to 10pm
UV: 0.1pm
X-rays: 1nm to 10-11
Gamma Rays: 10-11 to 10-13
What are the frequencies of EM waves from smallest to greatest?
Radiowaves: 300kHz to 300GHz
Microwaves and IR: 300GHz to 4x1014
Visible Light: 4x1014 to 7x1014
UV: 8x1014 to 3x1017
X-rays: 3x1017 to 3x1019
Gamma Rays: 3x1019 to 3x1021
What are polarised waves?
Transverse waves that have an electrical field oscillating in one plane
