Waves Flashcards
State Malus’ law.
I2 = I1 cos^2 (theta)
If the amplitude of the light passing through the second vector is E2 = E1 cos (theta)
Define wavelength.
The distance between two successive points on a wave that are in phase
What is a longitudinal wave?
Progressive waves whose displacements are parallel to the direction of energy flow. They require a medium and include compressions and rarefactions
What is phase difference and what is it measured in?
How much a particle/wave lags behind another particle/wave. Measured in radians, degrees or fractions of a cycle
How can you find out the time period of a wave using its frequency?
Time period = 1/frequency
Define amplitude.
The maximum displacement of the wave from its equilibrium position
Define frequency and give its units.
The number of waves passing a point per second, measured in hertz, Hz
What is the Principle of Superposition?
When two or more waves meet, the resultant displacement of the medium is the algebraic sum of the individual displacements
Other than electromagnetic radiation, give two examples of transverse waves.
Secondary ‘s’ waves
Water waves in a ripple tank
State two differences between a transverse waves and longitudinal waves.
In transverse waves the oscillation of the medium is perpendicular to the direction of wave travel
Transverse waves can be polarised
State one application of a polarising filter and a reason for its use.
Polaroid sunglasses - to reduce glare from a windscreen
The sound quality of a radio is improved by adjusting the orientation of the aerial. Why?
The radio waves from the transmitter are polarised so to improve the sound quality, the aerial should be aligned in the same plane of polarisation as the radio waves
By approximately how many times is the wavelength of audible sound waves greater than the wavelength of light waves?
10^6 times greater
What property of light waves do polarising sunglasses depend on?
Light waves may be polarised when reflected from a surface
Which wave has the greater frequency: light waves or sound waves?
Light waves have far greater frequencies than sound waves
Which wave has the greater wavelength: light waves or sound waves?
Sound waves have far greater wavelengths than light waves
Describe what an observer would see when a second polarising filter is rotated through 360º.
Variation in light intensity between maximum and minimum in 360º rotation
Why is it important to correctly align the aerial of a TV in order to receive the strongest signal?
Transmitted radio waves are often polarised to the aerial must be aligned in the same plane of polarisation
Describe the motion of a particle in a transverse wave.
It would oscillate perpendicular to the direction of energy transfer, from equilibrium to a maximum displacement, back to equilibrium then to a minimum displacement and back to equilibrium
Which of the following waves cannot be polarised?
a. radio
b. ultrasonic
c. microwave
d. ultraviolet
Ultrasonic as it is a longitudinal wave
State the characteristic features of longitudinal waves.
Particles oscillate parallel to the direction of energy transfer, in rarefactions and compressions
State the characteristic features of transverse waves.
Particles oscillate perpendicular to the direction of energy transfer, in peaks and troughs
What is the equation for wave speed?
c = f x (lamda) v = f x (lamda)
What is detected by a microwave detector when it reaches a maxima of intensity?
Maxima are antinodes - two waves interfere constructively giving large amplitude and much energy is stored there
What is detected by a microwave detector when it reaches a minima of intensity?
Minima are nodes - two waves interfere destructively and cancel out so amplitude equals 0 and no energy is stored there
Give 5 key features of a stationary waves.
- 2 progressive waves
- travelling in opposite directions/reflected
- same amplitude
- same frequency
- overlap and obey laws of superposition
How would you calculate the frequency of an overtone?
f4 = f1 x 4
Frequency of overtone = fundamental mode times the number of loops
A stationary wave is set up on a string with length l, and diameter d.
Another wave is set up on another string with equal tension and same material. What l and d are needed for the same fundamental frequency as the first string?
l/2, 2d
As f, (rho), T and 4 are constants, and L x D = constant
The frequency of the first harmonic is f. The length and tension are doubled, what is f now?
f / (square root of 2)
Why could actual frequencies on a stretched string be different to predictions
Diameter of the string may be reduced as it is stretches, giving a lower mass per unit length and therefore a higher frequency than anticipated
What is the equation for wavelength using time period, T?
(lamda) = v / (1/T)
What is the equation for phase difference?
phase difference = (2 pi x path difference) / (lamda)
2 pi can be exchanged for 360 if answer wanted in degrees
What is the degree equivalent of phase difference pi/3 radians?
pi / 3 = 60º = 1/6 of a wavelength
What is the degree equivalent of phase difference 2 pi/5 radians?
2 pi / 5 = 72º = 1/5 of a wavelength
What is the degree equivalent of phase difference 2 pi/3 radians?
2 pi / 3 = 120º = 1/3 of a wavelength
What are the two types of seismic waves, and what type of wave is each?
Primary waves are longitudinal, secondary waves are transverse
Define a transverse wave.
Progressive waves whose displacements are perpendicular to the direction of energy transfer. They do not require a medium and contain crests and peaks
Describe the motion of a particle on a transverse wave over one complete time period.
The particle oscillates about the equilibrium position vertically upwards to a maximum positive displacement, down to a maximum negative displacement, and up to the equilibrium position
Describe the relationship between the magnetic field variation and the electric field variation.
They are perpendicular to each other
When discussing the plane of vibration, which field are we looking at and why?
The electric field as the electric field causes the magnetic field
What are the four ways of producing plane polarised light?
Transmission (main), Reflection, Refraction, Scattering
Outline how cellophane produces plane polarised light.
It is an optically active material that rotates the plane of polarised light. The angle of rotation is dependent on thickness and wavelength
Give an example of light that is plane polarised due to reflection.
Water on the ground reflects light which is horizontally plane polarised
How can a camera use polarisation?
The polarising filter reduces reflected, plane polarised light, making it easier to take photographs through glass
How can calcite crystals produce plane polarised light?
They exhibit double refraction, splitting the light into two plane polarised rays that are mutually perpendicular, termed ordinary and extraordinary
How can some signals be detected from a microwave source with a filter at 45º to the horizontal?
The microwave can be split into two components, one of which is absorbed by the filter and the other passes through the filter
How is a sonic boom formed?
As an object travels faster than the speed of sound, the sound waves it produces overlap, forming a Mach cone. When the object has passed, the observer will hear a sonic boom
What is the approximate wavelength of radio waves?
10^3 - 10^1 metres
What is the approximate wavelength of microwaves?
10^-2 metres
What is the approximate wavelength of infrared radiation?
10^-4 metres
What is the approximate wavelength of visible light?
10^-6 metres
What is the approximate wavelength of ultraviolet light?
10^-8 metres
What is the approximate wavelength of x-rays?
10^-10 metres
What is the approximate wavelength of gamma rays?
10^-12 metres
Define constructive interference.
Two or more waves meeting at a point enhance one another at all times.
Define destructive interference.
Two or more waves meeting at a point oppose one another at all times and have zero resultant
