Particles & Waves Sub Unit Test Flashcards
What is interference?
Occurs when waves from two or more sources meet
What is the resultant wave from inference determined by?
The amplitude and relative phase of the waves
What happens when two wave meet in phase?
Constructive interference
What does ‘in phase’ mean?
When the crests meet the crests and the troughs meet the troughs of another wave
What happens when waves are constructive?
Form a singular wave of greater amplitude
What happens when two waves out of phase meet?
Destructive interference
What does ‘out of phase’ mean?
When crest meets trough
What happens when waves are destructive?
The waves cancel each other out
What does it mean for waves to be coherent?
Same frequency
Same wavelength
Same velocity
What is a maxima?
Maxima are regions where two waves meet in phase and interfere constructively.
In terms of speakers, these are loud regions
In terms of light, these are the bright points
What is a minima?
Regions where two waves meet out of phase and interfere destructively.
In terms of speakers, these are the quiet regions
In terms of light, these are the dull/blank regions
What is path difference?
The extra distance travelled by one wave source compared to another source
How do you work out the path difference for constructive interference?
p.d. = m x wavelength
where m = 0,1,2 (which is what point it is)
How do you work out the path difference for destructive waves?
p.d. = (m + 1/2) x wavelength
where m = 0,1,2, 3
How would you work out the wavelength of something when given the distance between two speakers and the maxima/minima?
Work out p.d. by distS2p -distS1p
Sub into p.d. = m x wavelength
Rearrange to find wavelength
What is Young’s double slit experiment?
Passes light through a narrow slit then using two slits to divide the waves which produces bright and dark fringes on a screen
In diffraction, what happens to the fringes when the distance between the two slits (2) increases?
Fringes are closer together
What happens when the distance (D) between the slits and the screen increases?
The distance between the fringes increases
What is a diffraction grating?
A series of narrow parallel slits etched onto glass
What happens when the number of slits on a diffraction grating increase?
A series of bright sharp lines are produced
What does m=0 mean?
There is no path difference
What does m=1 mean?
There is a path difference is exactly on wavelength
pd = 1 x wavelength
If the diffraction grating is given in lines per mm, how would you find d?
Convert into metres by dividing by 1000
d = 1/no. of lines per metre
What happens when a wave moves from one medium to another?
Wave changes speed, can lead to a change in direction
What is the change of direction when a wave moves from one medium to another referred to as?
Refraction
What happens to the velocity, frequency and wavelength of a wave been it enters glass from air?
Velocity decreases
Frequency remains unchanged
Wavelength decreased
When does the direction of a wave change in diffraction?
When it enters a medium at an angle
What is the refractive index of a median?
A measure of how much the material changes the speed of light when it passes through it. Also a measure of the direction change
What is the symbol for refractive index?
n
What is the absolute refractive index in a vacuum and air?
1.00
How would you calculate the refractive index?
n = sin theta in air / sin theta in material n = V in air / V in material n = wavelength in air / wavelength in material
What is the critical angle?
The angle of incidence for a material that results in an angle of refraction of 90 degrees
What is total internal refraction?
When the angle of incidence is greater than the critical angle and all the light is reflected inside the material.
What is a uses of internal reflection?
Optical fibres
How would you calculate the critical angle?
sintheta = 1/n
where n=refractive index
What is irradiance?
The power of radiation per unit area
What is the symbol for Irradiance?
I
What are the units for irradiance?
Wm-2
(Watts per metre squared
What is the relationship between irradiance and distance?
As the distance from the source increases, the irradiance decreases
What would a graph of distance against irradiance look like?
Same shape as a cooling curve
What is the purpose of the inverse square law?
To prove that irradiance varies with the square of the distance from the source
i.e. doubling the distance results in a quartered irradiance
Describe an experiment to verify the inverse square law of light.
Place a lamp at one end of a metre stick and a light intensity metre at the other end
Use the light detector to record intensity levels at different known distances from the lamp
Repeat the measurements
Describe how apparatus could be used to verify the inverse square law for a point source of light.
(With the lamp, metre stick, and the light intensity metre)
Obtain values of irradiance for different distances
Plot graph of I against 1/d2 (1 divided by distance squared)
Graph of I against 1/d2 is a straight line through the origin to prove that it is constant
What are the formulas to find irradiance?
I = P/A I = k / d2 I = 1 /d2 I1d1 = I2d2
When are line spectra emmited?
When an electric current passes through a low pressure gas
Why is spectra described as an atomic fingerprint?
Because each element has its own unique line spectrum
How can line emission be observed?
With a spectrometer using a diffraction grating or a prism
What can spectra be used for?
Identify elements present in distant stars and galaxies
Measure redshift of galaxies
Determine the rate of universal expansion
What creates line spectra?
The transition of of electrons between energy levels
How do absorption lines in sunlight spectrum allow us to determine the elements present in the suns atmosphere?
As light from hotter regions of the sun pass through cooler regions of the upper atmosphere, atoms absorb light at specific frequencies/wavelengths to produce an absorption spectra. These absorption lines allow the elements present to be identified.
What is meant by continuous spectra?
Spectrum of light with no visible separate spectra lines
How do electrons move between orbits?
Can adopt a new orbit level but cannot stop in between the electron levels
What is the lowest energy level of electron orbiting called?
Ground state
What is it called when an electron moves to a higher energy level?
It is in an excited state
What does ionisation level mean?
That an electron has gained sufficient energy to escape from the atom completely
When does an electron have zero energy?
When it has reached the ionisation level
Why does an electron being ionised have zero energy?
Because electrons have a negative energy, so to get to zero requires a lot of energy
When is delta E used?
When comparing energy levels in atoms
When and where to electron transitions take place?
Where = between the energy levels of an atom When = an electron either absorbs or emits a photon of electromagnetic radiation
What does E=hf relate to?
The frequency of an emitted photon
where h is plancks constant
What is the relationship between the jump in electron levels and the frequency of the photon emitted?
As the size of the jump increases, the frequency of the photon emitted also increases
Describe how an electron can make the transition to a higher energy level.
By absorbing a photon of the electromagnetic radiation that had energy equal to precisely the difference between energy levels
Describe the process of an electron moving from a higher energy level to a lower energy level.
The electron loses energy as it moves to a lower energy level and emits a photon in the process. The energy of the photon is equal to the difference between levels
