3.3 WAVES Flashcards
What is the optimal size of a gap for a wave to diffract through?
One that is similar sized/slightly larger than the wavelength of the travelling wave. Waves bend around the gap, and interfere with each other (light has to bend around sharper corners)
Explain why there is little diffraction when a wave travels through a gap greater than its wavelength
Waves will not be able to combine and produce an interference pattern. This is because the gap is too large for the waves to bend around and interfere with each other
Explain why there is no diffraction when a wave travels through a gap smaller than its wavelength
Waves simply reflected back
Waves do not have to refract much and therefore there is limited interference according to some site
this is wrong app
What determines the resolution of a microscope?
The size of the objective lens relative to the wavelength of light
If the objective lens is much larger than the wavelength of the light, the diffraction pattern will be small and the resolution of the microscope will be high. However, if the objective lens is about the same size as the wavelength of the light, the diffraction pattern will be larger and the resolution of the microscope will be lower
Explain why a light microscope can’t view objects smaller than the wavelength of visible light
The light from the microscope will diffract around the edges of the object, causing the image of the object to blur. As the size of the object decreases, the diffraction of the light increases, causing the image to become even more blurred. This makes it impossible for a light microscope to resolve objects that are much smaller than the wavelength of light because the diffraction of the light causes the image to blur.
What is the optimal size for the wavelength of an electron used to investigate the size of gaps between atoms?
(in electron microscope)
in the order of 10^-10m (ask mrgray)
What makes something exhibit more wave like properties?
Having a longer wavelength
Why do objects travelling at higher speeds diffract less?
Shorter wavelength, less diffraction
λ = h/mv
What is the frequency range of visible light?
650nm (deep red) to 450nm (deep violet)
If i need saving
https://www.youtube.com/watch?v=TqTWSSBcV_4
https://www.youtube.com/watch?v=b6prlN4Fz90
What is a progressive wave?
A (moving) wave that transfers energy without transferring matter
What are examples of how waves transfer energy
- EM waves cause things to heat up
- X rays are ionising
- Source of waves loses energy as
wave propagates
Why can’t longitudinal waves be polarised?
polarisation restricts the vibrations to one
plane by absorbing the vibrations at right angles
to this plane
* longitudinal waves cannot be polarised
because the vibrations have to take place for
energy to be transmitted
The vibrations of a longitudinal wave occur along a single line, it is therefore not possible to confine that to a plane, i.e. a 1D shape cannot be confined within a 2D shape.
How does polarisation provide evidence for the nature of transverse waves?
Polarisation requires the direction of oscillation to be perpendicular to propagation
The reason that only transverse waves can be polarised is that their vibrations can potentially occur in all directions perpendicular to the direction of travel. It is therefore possible to confine the vibrations to a single plane
What is the plane of polarisation of an EM wave defined as?
The plane which the electric field oscillates in
Phase difference in radians
2πd/λ 2πt/T
What are puretone sound waves?
Sound waves of a single frequency
What does LASER stand for? [6]
Light amplification by stimulated emission of radiation
Describe how a standing wave is formed on a taut string
- String is fixed at either ends (to a
weight/wall) [lossless system] - Progressive wave sent along the
string - When wave reaches the end of the string, reflected wave begins to travel in the opposite direction
- Wave must have similar frequency/amplitude
When the two waves meet, they superpose.
Nodes - where 2 progressive waves are always in antiphase, destructive
Antinodes - points where waves are always in phase, constructive
In between is a combo of both
As there is no oscillation at either end of the system, energy is “locked” and can’t be transferred through the standing wave
What are the equations for the nth harmonic frequency?
fn = v/λn = nv/2L
What is the first harmonic also referred to as
The fundamental mode
What is the equation to find the first harmonic frequency of a string?
f1 = (1/2L) * sqrt(T/μ)
where:
f1 is the frequency of the first harmonic mode of vibration (in hertz, Hz)
L is the length of the string (in meters, m)
T is the tension in the string (in newtons, N)
μ is the linear density of the string (in kilograms per meter, kg/m)
assuming the string is under ideal conditions, with negligible damping and a uniform linear mass density. It also assumes that the string is fixed at both ends and is vibrating in a single antinode
What is the principle of superposition?
When two waves meet, the total displacement at that point = the sum of the individual displacements at that point
What makes waves coherent
If they have a constant phase difference
Distance between adjacent node and anti/node
Node + node = 1/2λ
node + antinode = 1/4λ
What do pitch and loudness correspond to in a wave
Pitch - frequency
Loudness - amplitude
What is refraction
The changing of direction of a wave as it passes the boundary between 2 media
What is total internal reflection?
When all incident light reflects after hitting a boundary - Angle of incidence is greater than the critical angle (ray remains in original medium)
- Only possible when ray travels from high to low refractive index
What is the refractive index (n) of a material
The ratio of the velocity of light in a vacuum to its velocity in a specified medium
(The capacity of the material to change the speed of light)
All versions of Snell’s law
n= sini/sinr
c1/c2 =sini/sinr
n1sinθ1 = n2sinθ2
where 1 is 1st medium, and 2 is 2nd medium
Difference between refraction of light vs other waves
Light is changing direction after passing between 2 TRANSPARENT media
What happens when light travels from a material with a high refractive index to a low one
It bends away from the normal
(lower refractive index = higher speed relative to c)
Relate the refractive index of a material (s) to the ratio of the wavelengths of light coming in and going out
Ns = c/cs =λ/λs
As frequency is constant
Do water waves get faster or slower as they travel from deep to shallow water
Slower, as same drag force from the “seabed” acts against a smaller mass of waver, decreasing rate of flow
Wavefronts move closer to the normal, decreasing λ, while f is constant, so v decreases
What is white light?
Light containing a continuous range of all wavelengths