Waves Chapter 5 Flashcards
What are longitudinal waves
Waves which the direction of vibrating of the particles is parallel to along the direction in which the wave travels
Waves that are like a slinky
What are transverse waves
Waves in which the direction of vibration is perpendicular to the direction in which wave travels
Goes up and down
What is polarisation
Where it involves transverse waves which are in a plane polarised if the vibrations stay in one plane only.
Polarisation from one plane to another
Polarised from one plane to another the waves are in polarised
What happens if unpolarised light passes through a Polaroid
It transmits light is polarised as the filter only allows through light which vibrates in a certain direction, according to the alignment of its molecules
What happens if Unpolarised light passes through two Polaroid filters
The transmitted light intensity changed if one Polaroid is turned relative to the other one.
What happens if Unpolarised light passes through two Polaroid filters
Pt2
Crossed and transmitted intensity is a minimum this position shows the polarised light from the first filter cannot pass through the second filter as the alignment of molecules in the second filter is at 90⁰ to the alignment in the first filter.
Phase difference
Phase of a vibrating particles at a certain time is the fraction of a cycle it has completed since the start of the cycle.
The phase difference is between two particles vibrating at the same frequency is the fraction of a cycle between the vibrations of the two particles measured either degrees or radians.
Wave speed info
Higher the speed and frequency of the wave shorter the wavelength.
Higher the frequency close together the wave peaks are
Wave speed equation
Wave speed = c = f x λ
C = distance travelled in one cycle / time taken for one cycle
C = λ÷ 1÷f
= fx λ
Parts of a wave
Amplitude - from middle line to the height of ether wave
Wavelength - from one wavelength to another
Trough - from the bottom of the wave to the middle line
Key terms
Displacement
Of a vibrating particle is it’s distance and direction from its equilibrium position
Key terms
Amplitude
Maximum displacement of a vibrating particle for a transverse wave it is distance from the middle to the peak of the wave.
Key terms
Wavelength
Least distance between two adjacent vibrating particles with the same displacement and velocity at the same time
Key terms
Cycle
When a vibrating particle is displaced unit is return to its stored.
Key terms
Period
Period of a wave is the same time for one complete wave to pass a fixed point
Key terms
Frequency
Numb of cycles of wave that pass a point per second
What’s a progressive wave
To distinguish them from stationary waves. They combine at fixed points along the rope to form point of no displacement or nodes along the rope. At each node the two sets of waves are always 180⁰ out of phase so they cancel each other out.
Antinode
Fixed point in a stationary wave pattern where amplitude is maximum
Node
fixed point in a stationary wave pattern where the amplitude is zero
Stationary wave
Stationary wave is formed when two progressive waves pass through each other
This can be achieved on a string tension by fixing both ends and making the middle part vibrate so progressive wave and travel towards each end reflects at the end and then pass through each other
Superposition
When two waves meet they pass through each other at a certain point where they meet, they combine for an instant before they move apart
The total displace at a point is equal to the sum of the individual displacement at that point
What happens when two crest meet
Make a super test created by two waves reinforce each other
What happens when two trough meet
Make a supertrough
What happens when a crest and a trough meet
If the both have the same amplitude the resultant displacement is zero the waves Cancel each other out if they are not the same amplitude the resultant is called a minimum
Frequency
F= c/λ
Wave speed
fλ = c
Wavelength
λ=c/f
The refractive index
N= sin i / sin r
Wavefront
Lien that connects all the point on a wave that are in phase
Refraction
Change of direction due to a change of speed caused by a change in density
What occurs to refraction
Retraction occurs because the speed of the light waves is ditterent in each substance. The amount of refraction that takes place depends on the speed of the waves in each substance.
Snells law calculation 1
Cst = sin(r) x XY Ct= sin(i) x XY Cst/sin(r) = XY = ct/sin(i)
Rearrange
Ct/cst = sin(i)/sin(r)
C/cs = sin(i) / sin(r) = N
Snells law calculation 2
N1 x sin(i) = N2 x sin(r)
Refractor equation
N1 x sin(i) ÷ N2 = Angle of refraction
Incidence equation
Sin(r) x N2 / N1
Critical angle
Sin0₁ = N2 / N1
What is critical angle
The angle of incidence where the refracted ray travels along the boundary between the two medium
Angle of i = critical
i = c
Total internal reflection occurs when
- i > c angle of incidence is larger than the critical angle
- Light travels from more dense to less dense medium
Sin0c = N2/N1
Optical fibres
Optical fibres are used in medical endoscopes to see inside the
body, and in communications to carry light signals.
What does optical fibres do
They allow pulses of light that enter at one end from a transmitter to reach a receiver at the other end
Total internal reflection takes place when
The cor cladding boundary at any point where two fibres are in direct contact light would cross from one fibre to the other if there were no cladding.
Medical endoscope
medical endoscope contains two bundles of fibres. The endoscope
is inserted into a body cavity, which is then illuminated using light sent
through one of the fibre bundles. A lens over the end of the other fibre
bundle is used to form an image of the body cavity on the end of the
fibre bundle. The light that forms this image travels along the fibres to
the other end of the fibre bundle where the image can be observed. This fibre bundle needs to be a coherent bundle, which means that the Fibre ends at each end are in the same relative positions.
Interference
Occurs when two coherent progress waves travelling in the same direction
Similar amplitude
Same frequency constant phase difference
Two waves diffract and super pose to form a regular interference pattern
Constructive interference
Occurs when the position of the path is difference a whole number of wavelength nλ
Destructive interference
Occurs when the path difference = a whole number plus half a wavelength n + 1/2 λ
Fringe separation
W= λ x D / s
D = distance λ = wavelength S = split spacing W = fringe separation
Double slit equation
S1 x P - S2 x P = m x λ
Two slits S1,S2
P point on the screen
M =1,2,3,4 etc …
Wavelength and colour
650nm
350nm
- Red light
2. Violet
Single slit diffraction width
W = λ / a x 2D
A = single slit D= split screen distance
Through a single slit
The central fringe is twice as wide as each of the outer fringes
Each of the outer fringes is the same width
Intensity
Peak intensity of each fringe decreases with distance from the centre
The outer fringes are much less intense than the central fringe
Diffraction wavelength
Greater the wavelength the wider the fringe
Width of the central fringe is proportional to the wavelength
Diffraction grating
diffraction grating consists of a plate with many closely spaced
parallel slits ruled on it. When a parallel beam of monochromatic light is directed normally at a diffraction grating, light is transmitted by the grating in certain directions only.
This is because:
the light passing through each slit is diffracted
Diffraction grating equation
D x sin0 = n x λ
Stationary wave equation
F= 1/ 2x L √ t/u
F= frequency L = length T= tension U = mass per unit length
Describe when some light is refracted and some light is reflected at a boundary
Internal reflection
Modal dispersion
The lengthening of a light pulse as it travels along an optical fibre due to rays that repeatedly undergo total internal reflection having to travel along distance than rays that undergo fewer total internal reflections
