Wave & quantum behaviour Flashcards
How is a standing wave made?
When 2 waves with the same wavelength travel through the same material in opposite directions
What is the difference between a node and an antinode?
Node = a place of no displacement on a standing wave
whereas antinode = a place of maximum displacement
When does constructive interference occur?
When waves are in phase and their path differences are a whole no. of wavelengths apart
When does destructive interference occur?
When waves are out of phase and their wavelengths are half a wavelength different
When does a path difference equal constructive interference? and destructive interference?
Constructive: when path dif. = a whole number of wavelengths
Destructive: when path dif. = not a whole number of wavelengths, e.g. 6.4pi
Equation for angular velocity
w = 2piF (frequency)
What is the principle of superposition?
Says that when 2+ waves overlap, the sum of the amplitudes of each wave equals the resultant displacement
What is the relation between energy/light intensity and amplitude?
Light intensity is proportional to amplitude^2
2 equations involving refractive index
n = sini / sinr n = 1 / sinC
When a wave crosses a boundary, what feature doesn’t change out of v, f, and wavelength?
Frequency doesn’t change. so v is proportional to wavelength
What is the speed of light and the speed of sound?
Speed of light = 3 x10^8 ms-1
Speed of sound = 343 ms-1
In the EM spectrum, which out of speed, wavelength and frequency is constant?
Speed is constant.
Which type of waves can be polarised and why?
Transverse, because they vibrate in multiple planes, whereas longitudinal waves vibrate in only one plane so can’t be polarised
If you have 2 polariser filters (polariser then analyser) in front of a light source, how do you change the brightness of light?
Rotate the 2ND filter, rotating the 1st won’t affect the brightness, though it does polarise the light
How can you position an analyser filter (the 2nd filter) to cut out all light from a source?
Align it at 90 degrees to the polariser
Equation relating number of fringes, wavelength and slit separation
dsinø=n lambda
How can you tell the amplitude of a wave from the number of slits?
Number of slits = amplitude
Why does 3 slits mostly not create any completely dark spots in between fringes, like 2 slits does?
-.- -.-.- =.=.=.=.= -.-.- -.-
Because 3 slits means there are 3 phasors (e.g. at 0, pi, 2pi) so as two cancel out another phasor will remain, creating 1/9 of the brightness, resulting in many places having dots of light rather than no light
Does
a) a wide slit
b) a narrow slit
create narrow or wide patterns?
a) wide slit = narrow pattern
b) narrow slit = wide pattern
How does the spacing of slits affect the spacing of fringes?
Closer together slits = further apart fringes
Further apart slits = closer together fringes
What is the fundamental frequency on a standing wave?
It’s the frequency of the longest standing wave that can be created on a string (i.e. the largest frequency). Wavelength = 2L
Why does a long, closed (at one end) tube give lower notes than an open tube?
Because it’s got a lower fundamental frequency since there would be a node at the closed end and an antinode at the open end, so it’s wavelength = 4L, whereas if it’s open with antinodes at both ends, its wavelength would = 2L.
So a closed tube has a lower frequency + longer wavelength = lower notes
How do you get a sharper interference pattern?
Diffract the light through more slits (the bright bands become brighter and narrower)
Equation for the energy carried by a quantum
E = hf
h=6.63x10^-34
What is 1 eV equal to in joules?
1 eV = 1.6x10^-19 J
What is the Photoelectric effect?
It’s when a light with a high enough frequency is shone onto the surface of a metal and causes electrons to be emitted
How do you increase the maximum kinetic energy of photoelectrons?
Increase the light frequency
What happens if the light intensity is increased?
It increases the rate of photoelectrons emitted
intensity is proportional to no. photoelectrons emitted per second
If light shone on a metal has ‘just enough’ energy to release electrons, what is the work function equal to?
E=hf= work function
How does an electron move down an energy level?
By emitting a photon
Why does the PE effect only occur after the incident light has reached a certain frequency?
- An electron needs to gain a certain amount of energy (the work function) before it can eject
- and an electron can only absorb one photon
- Energy an electron can absorb depends on the frequency of the light
What does excitation mean?
The movement of an electron to a higher energy level by absorbing energy
Equation relating probability and the resultant phasor amplitude
Probability of photon arrival is proportional to (resultant phasor)^2
How does light travelling through a different material (e.g. water) affect its path?
In water light slows down, but frequency stays the same. So the photons still have the same energy and its phasor has the same amplitude.
What is the de Broglie equation?
wavelength = h / p
p=mv=momentum
If you conduct Young’s double-slit experiment with electrons, what do the bright and dark fringes tell you?
Bright fringe = an area with high probability of an electron arriving there
Dark fringe = an area with low probability of an electron arriving there
Why are the levels negative in an energy level diagram?
Because electrons in the atom are bound to the nucleus
Why are the levels negative in an energy level diagram?
Because electrons in the atom are bound to the nucleus
What do you use to polarise microwaves instead of a filter and why?
A metal grille - microwave wavelength is too long for a filter
When is the intensity of a polarised microwave at a maximum?
When the metal grille is at a righ angle to the vibration of waves
What is the intensity of a polarised microwave when the grille is aligned with the direction of wave vibration?
Intensity = 0
Explain why the intensity is 0 when the grille is aligned with microwaves’ direction of vibration
- Electric field of wave excites grille electrons
- Grille absorbs energy from wave
- Re-emits energy in all directions
- Unlikely to be picked up by receiver which only receives in one plane
- So intensity reading at receiver is 0
