waves and the particle behaviour of light Flashcards
what is a transverse wave
A type of wave in which the particles oscillate at right angles to the direction the waves travel
what is a longitudinal wave
a type of wave in which the particles oscillate parallel to the wave direction
what is wavelength
the distance between two matching points on neighbouring waves
what are rarefactions
regions in a wave where the medium is less dense compared to the surrounding areas.
what are compressions
regions of increased density in a wave.
what is period
the time taken for one complete oscillation
if an oscillator has a frequency of 10Hz what will be the oscillations per second
10
what is frequency
the number of oscillations per second
what does monochromatic mean
have the same wavelength
what is superposition
when two or more waves overlap in space, the resulting amplitude is equal to the sum of the individual amplitude
what is a wave when it is in phase
the position within the oscillation of a wave so their troughs and crests are aligned
what is constructive interference
happens when the resultant wave has a larger amplitude than any of the individual waves
what is destructive interference
happens when the resultant wave has a smaller amplitude then the individual waves
what is amplitude
is the maximum displacement of a particle in the wave from its equilibrium position (from equilibrium to peak or trough)
what is antiphase
when the crest of one wave aligns with the trough of another
what is wavefront
an imaginary surface or line that connects all the points of a wave that have the same phase
what does coherent mean
so when they have constant relative phase or when they have zero or constant phase difference and the same frequency
give two definitions of a standing wave
1.oscillates in time but does not move in space
2.con only be formed when a waves motion is restricted within a given finite space
give two definitions of a progressive wave
1.moves continuously in a medium in the same direction
2.can be either longitudinal or transverse
state the relationship between gap distance and wavelength
partial diffraction D > λ
full diffraction D = λ
no diffraction D < λ
what is Huygens principal
all points of a wavefront of sound in a vacuum or transparent medium
(air) may be regarded as a new sources of wavelets what expand in every direction at a rate depending on their velocities
what does the diffraction pattern show in Youngs double slit experiment
- constructive interference between light rays form bright strips called fringes (interference fringes or maxima) on the screen
- Destructive interference forms dark strips, also called dark fringes (or minima) on the screen
how can we describe the fringes in the double slit experiment
identical and has the same width and intensity
what does the interference pattern show
the regions of constructive and destructive interference (light and dark fringes)
what is each bright fringe equal to
a peak of maximum intensity
what does each dark fringe show
a trough of minimum or zero intensity
what are maxima
formed by the constructive interference of light
what are minima
formed by the destructive interference of light
what is phase difference
how far apart the waves are when comparing their phases
what is phase difference measured in
radians
what is 1 radian
1 radian is equal to 57.2958Deg
how do you calculate 1 radian
1Rad × 180/π and reverse for degrees
why do we use a circle to to represent a wave
a circle is symmetric and starts to change in height fast near the x axis, but gets slow near the y axis
explain diffraction grating
Diffraction gratings are formed by large numbers of equally spaced slits or lines that diffract the light falling on them. The path difference between two adjacent slits is the same as in the double slit case, x=dsinθ. So the condition for a maximum remains the same
how do you calculate diffraction gratings
nλ = dsinθ
what is path difference
The difference in distance travelled by two waves from their sources to the point where they meet
how are path differences measured in
multiples of wavelengths
what is light
light is the fluctuation of electromagnetic waves at right angles to electric fields
what is another unit for photon charge instead of joules
electron volt
what is the definition of the electron volt
equal to the kinetic energy gained by an electron when it is accelerated by a potential difference of one volt
why do we use a electron volt
joules is too large of a unit
what is the value of a electron volt
1.16*10^-19
what is ionisation
the removal of a electron from its atomic outer shell resulting in a delocalised electron and a positive atomic ion this happens when the atom is hit by another energy source
what is the name of the energy that the incident particle gives off
ionisation energy
what are the main causes of ionisation
usually radiation but sometimes heat particles
what is excitation
the promotion of electrons from lower to higher energy levels within an atom
why do electrons de excite
exited states are usually very unstable and due to the positive attraction of the atoms nucleus the electrons are forced down into a lower energy level
what is the bi product of de excitation
photons
how can we express emitted photon energy
hf = E2 - E1
what are the conditions of excitation
when the photon energy is exactly equal to the energy required to excite
what is plancks constant
6.63*10^-34 js
how are standing waves formed (6 marks)
-in a medium when two waves having equal amplitude and frequency
-in opposite directions along the same line
-in a confined space
-formed by superposition of a forward wave and the reflective wave
give the equation for the first harmonic
L = 1/2*λ
the second harmonic equation
L = 2/2*λ
the third harmonic equation
L = 3/2*λ
the n’th term harmonic
L = n/2*λ
how do you rearrange the harmonics equation to give lambda
λ = 2L
