Chapter 11,12 - Waves Flashcards
Outline progressive wave
An oscillation that travels through matter or a vacuum, transferring energy from one place to another, but not transferring matter. The particles in the matter vibrate as the wave passes through them, but they do not move along with the wave.
Define transverse wave and give examples
Oscillations are perpendicular to the direction of wave travel or energy transfer. They have peaks and troughs at maximum and minimum points of displacement.
E.g. Electromagnetic waves or water surface waves
Define longitudinal waves and give examples
Oscillations are parallel to the direction of wave travel or energy transfer. They have areas of compression, where particles are close together, and areas of rarefaction, where particles are more spread out.
E.g. sound and seismic p waves
Displacement
The distance from the equilibrium position in a particular direction
Amplitude
Maximum displacement from the equilibrium position
Wavelength
Minimum distance between two adjacent points on a wave oscillating in phase
Period
Time taken for one complete oscillation of one wavelength to pass a given point
Frequency
The number of complete oscillations passing a given point per unit time
Wave speed
The average distance travelled by a wave per unit time
Phase difference
Difference in displacement of particles along a wave, or in two different waves.
Phase difference for particles in phase
multiple of 2pi or 360 degrees
Phase difference for out of phase particles
separation in wavelengths between particles / wavelength x 360 degrees
In phase and in antiphase
in phase = 0 or 360 degrees
antiphase = 180 degrees
Equation for time period
1/frequency
wave equation
v=fλ
Can progressive waves be reflected, refracted and diffracted?
Yes
Define reflection and the law of
when a wave changes direction at a boundary between two media, angle of incidence = angle of reflection
what happens to the wavelength and frequency after reflection
Stay the same
Define refraction
When a wave changes direction due to a change in speed, when it enters a new medium.
What happens to wavelength and frequency after refraction
- frequency remains constant
- but if speed increases, v=fλ states that λ must also increase
What happens to the speed of sound through denser materials
speeds up
What happens to em wave speed through denser materials
slow down
What will always happen to light incident on a surface
partial reflection
Define diffraction
the spreading out of a wave front as it passes through a gap
What happens to λ, v and f after diffraction
stay the same
When will maximum diffraction occur
when the gap the wave passes through is the same size as the wavelength of the incident wave
Can longitudinal waves be polarized?
No as direction of energy transfer is already parallel to oscillations, only transverse waves can be polarized
Define plane polarisation
A wave that only oscillates in one plane, e.g. vertical propagation
Why is light so hard to diffract?
such a small wavelength so require such a small gap
Explain what partial polarization is and why sunglasses can be designed using them
- When there are more wave oscillating in one particular plane, but the wave isn’t completely plane polarized.
- Light reflected off water is partially polarized.
- Most of this light is oscillating in the horizontal plane and so sunglasses can contain polarizing filters which allow only one plane of light to pass through, reducing the glare reflected off flat surfaces like lakes
Define Intensity of a progressive wave
Radiant power passing at right angles through a surface per unit area
- I = P/A
Relationship of intensity and amplitude
Intensity α Amplitude squared
Define electromagnetic waves
Transverse progressive waves consisting of magnetic and electric fields which oscillate at right angles to each other and can travel through a vacuum.
Order of EM spectrum from longest λ to shortest
Radio (low frequency) Micro Infrared Visible Ultraviolet X-ray Gamma (high frequency)
Order of visible light spectrum from longest λ to shortest
Red Orange Yellow Green Blue Indigo Violet
λ of radiowaves
10^3
λ of microwaves
10^-2
λ of infrared
10^-5
λ of visible
0.5x10^-6
λ of ultraviolet
10^-8
λ of x-ray
10^-10
λ of gamma
> 10^-12
equation for refractive index
n = speed of light in vacuum / speed of light in medium n = c/v
angle to determine angle of refraction , θ1
n1sinθ1 = n2sinθ
how do you measure angles of refraction and reflection
to the normal
define total internal reflection
Occurs at a boundary between two transparent media , with no refraction - all of the light incident on the boundary is reflected back into the original medium.
Conditions for total internal reflection
- light must be travelling from a high refractive index to a low refractive index
- the angle of incidence of the ray to the normal must be the critical angle
what is the critical angle
angle of incidence when the angle of refraction is 90 degrees
equation for critical angle
sinC = 1/n
however only useful if original medium is air
Principle of superposition
when two waves meet at a point, they overlap and superpose, the resultant wave at that point is equal to the sum of the displacements of the initial waves.
define coherent
waves emitted with constant and unchanging phase difference
Define interference
Superposition occurring between two coherent waves
How to tell if constructive or destructive interference is occurring?
constructive has even phase differences of 0, 2π, 4π, 6π….
destructive has odd phase difference of π, 3π, 5π
what is monochromatic light
light of only a single wavelength
Young’s double slit equation
λ = ax/d
where a is the slit separation
x is the distance between two adjacent maxima
d is the distance from the screen
what is a diffraction grating
piece of transparent material with many opaque lines scratched onto it
Equation for order maxima
dsinθ = nλ
where n is the maxima number
stationary waves
a series of alternating nodes and antinodes
Formation of stationary waves
formed when two progressive waves with the same frequency and ideally amplitude, travelling in opposite directions, superpose.
node
point of no movement with zero amplitude
antinode
point of maximum displacement
equation for phase difference on a wave
180 degrees x n where n is the number of nodes between the two points
Do stationary waves transfer energy
No, they store it
what is the fundamental frequency
lowest possible frequency of vibration
what does the number of nodes on a stationary wave depend on
frequency
table of harmonics
in textbook
stationary waves
a series of alternating nodes and antinodes
Formation of stationary waves
formed when two progressive waves with the same frequency and ideally amplitude, travelling in opposite directions, superpose.
node
point of no movement with zero amplitude
antinode
point of maximum displacement
equation for phase difference on a wave
180 degrees x n where n is the number of nodes between the two points
Do stationary waves transfer energy
No, they store it
what is the fundamental frequency
lowest possible frequency of vibration
what does the number of nodes on a stationary wave depend on
frequency
table of harmonics
in textbook
stationary waves
a series of alternating nodes and antinodes
Formation of stationary waves
formed when two progressive waves with the same frequency and ideally amplitude, travelling in opposite directions, superpose.
node
point of no movement with zero amplitude
antinode
point of maximum displacement
equation for phase difference on a wave
180 degrees x n where n is the number of nodes between the two points
Do stationary waves transfer energy
No, they store it
what is the fundamental frequency
lowest possible frequency of vibration
what does the number of nodes on a stationary wave depend on
frequency
table of harmonics
in textbook
