M4C4 Flashcards
Name and describe the two types of progressive waves
- Transverse waves have particle motion that is perpendicular to the direction of wave propagation.
- Longitudinal waves have particle motion that is parallel to the direction of wave propagation.
What are progressive waves?
Waves that transfer energy away from a source
What is the wave equation?
v = f λ v = velocity (m s^-1) f = frequency (Hz or s^-1) λ = wavelength (m)
Define wavelength
The wavelength of a wave is the distance between two successive identical points that have the same pattern of oscillation. It is also the distance the wave travels before the pattern repeats itself.
Define period (t)
The period of a wave is the time it takes for one complete pattern of oscillation to take place at any point.
Define frequency
The frequency of a wave is the number of oscillations per unit time at any point and is related to the time period T by the equation f = 1/T
Define displacement in terms of waves
Displacement is the distance any part of the wave has moved from its mean (or rest) position - it can be positive or negative.
Define amplitude in terms of waves
Amplitude is the maximum displacement - the distance from a peak or trough to the mean (rest) position.
Define phase difference
Phase difference concerns the relationship between the pattern of vibration at two points. Two points that have exactly the same pattern of oscillation are said to be in phase - there is zero phase difference between them.
What is the equation for intensity?
I = P/A I = intensity (W m^-2) P = power output of the source (W or J s^-1) A = area over which the radiation falls (m^-2)
What is the formula for the speed of sound in air?
331+0.6T
T= temperature
What’s the relation between intensity and amplitude?
intensity ∝ (amplitude)^2
What is the refractive index equation?
refractive index = sin(i)/sin(r)
i = angle of index
r = angle of reflection
Define diffraction
Changes in the directions of waves can also occur when they meet an obstacle, or as they pass through an aperture. This is called diffraction.
For maximum effect, the aperture needs to be the same size as the wavelength of the wave.
Define interference
This occurs when two waves meet and occupy the same space at the same time.
Effectively they can add together to make a larger wave (peak + peak), or they can cancel each other out (crest + trough).
This adding and subtracting of waves causes an interference pattern.
What are the properties of electromagnetic waves?
- travel through a vacuum.
- interlocked magnetic and electrical waves at right angles to each other.
- c = 3.0x108 m s-1 (or 2.98x108 m s-1).
- transverse.
- reflected, refracted and diffracted.
- interference and polarisation.
Whats the difference between x-rays and gamma rays
X-rays and gamma rays are often identical in terms of their energies, wavelength and frequencies. The only difference between them is how they are produced. X-rays are made by accelerated electrons outside the nucleus, but gamma rays are always emitted from the nucleus of an atom.
What type of wave can be polarized?
Transverse
What’s malu’s law?
When a perfect polariser is put in a beam of polarised light, the intensity, I, of the light that passes through it is given by I = Imaxcos^2 θ, where I is the intensity transmitted at angle θ. Also, Imax is the maximum intensity transmitted at θ = 0^o.
If the analyser is at right angles to the the polariser, then θ = 90^o and no light will pass through. This situation is known as ‘crossed Polaroids’
What is the polarization equation?
I = Imaxcos2θ Imax = the maximum intensity transmitted (at θ = 0^o). θ = angle between the initial polarisation direction and the polariser axis of polarisation.
What is the equation for finding the refractive index?
n = c/v n = refractive index c = speed of light in a vacuum v = speed of light in material
What is Snell’s law?
n1sinθ1 = n2sinθ2 nsinθ = c n1 = refractive index of first material θ1 = angle light enters the first material n2 = refractive index of the second material θ2 = angle light enters the second material n = refractive index c = speed of light in a vacuum
When does total internal reflection take place?
It occurs when the angle of refraction is above of equal to 90^o
Define superposition
The adding together of the displacements of two waves.
Define constructive interference
The result of two waves arriving at a single point in phase (ɸ = 0 o or 2𝜋 rad) with each other
Define destructive interference
The result of two waves arriving at a single point in antiphase (ɸ = 180 o or 𝜋 rad) with each other
Define coherence
When two waves have a constant phase difference, they are said to be coherent with each other
Define path difference
The difference between the distances travelled by two waves arriving at the same point (measured in m)
Define phase difference
The difference in the phases of two waves of the same frequency (measured in radians)
What is the equation associated with the Young double slit experiment?
λ = ax/D
λ = wavelength (m)
a = distance between slits (m)
x = distance between the ‘straight through’ and the 1st bright fringe (m)
D = distance between slits and screen (m)
This equation only applies if a «_space;D keeping θ less than 10^o
What is the number of the pattern, n, on either side of the central maximum is known as?
Order
What is the diffraction equation?
n λ = d sinθ n = order of the maximum (no units). λ = wavelength of light (m). d = slit separation (m). θ = angle that the beam makes with the grating (degrees or rads)
What is a standing wave?
A wave that has its energy confined to a fixed position
What is a node in relation to standing waves?
Nodes are points in a stationary wave at which there is no displacement of the particles at any time
What is an anti-node in relation to standing waves?
A point in a standing wave with maximum displacement
What conditions must be met to produce a standing wave in a sting or pipe?
The two waves that overlap must be travelling in opposite directions, have the same frequency and have approximately equal amplitudes.
What are the standing wave equations for string?
L=1/2λ L=2/2λ L=3/2λ L = length of string λ = wavelength
What are the standing wave equations for a open pipe?
L=1/4λ
L=3/4λ
L = length of string
λ = wavelength
What are the standing wave equations for a closed pipe
L=1/2λ L=λ L=3/2λ L = length of string λ = wavelength
