5 Waves Flashcards
Amplitude
The max displacement of a particle from the midpoint of the oscillation (m)
Time period
The time taken to complete one oscillation (s)
Frequency
The number of oscillations per second (Hz)
Wave speed
The distance travelled by the wave each second (m/s)
Wavelength
The distance between consecutive points at which oscillations are in phase
Equation linking frequency and time period (learn)
f= 1/T
Equation velocity frequency and wavelength
V=f x wavelength
Longitudinal waves
When particles oscillate in the same direction as the wave travel
Transverse waves
When particles oscillate perpendicular to the wave direction
Wavelength of gamma rays
10^-16 to 10^-11
Wavelength of x-rays
10^-14 to 10^-10
Wavelength of ultra violet
10^-10 to 10^-8
Wavelength of visible light
4x10^-7 to 7x10^-7
Wavelength of infrared
10^-7 to 10^-3
Wavelength of microwaves
10^-4 to 10^-1
Wavelength of radio
10^-3 to 10^5
Properties of gamma rays
Destroying tumours
Properties of x rays
See bones
Properties of ultraviolet
Checking banknotes
properties of Visible light
Photosynthesis and to see
Properties of infrared
Night vision
Properties of microwaves
Mobile phones and satellite communications
Properties of radio
Many signals can be transmitted
Equation of intensity power and area
I= P/A
Constructive superposition
When two waves are in phase and make a larger waves
Destructive superposition
When two waves are completely out of phase and cancel out
When are waves coherent
- same type
- same frequency
- constant phase difference
Path difference
The difference between the distances from two sources to a given point
When is an interference pattern observed?
- they are two coherent sources
* they have a similar amplitude
Standing waves
When two waves of equal frequency and amplitude are travelling at the same speed in opposite directions superimpose
At antinodes what is the path difference
Zero path difference so max amplitude
At nodes what is the path difference?
Half a wavelength pi/2 therefore there is min amplitude
Characteristics of progressive waves
- energy is transferred in direction of wave travel
- all points on wave have some amplitude
- adjacent points in wave have a different phase relationship
Characteristics of standing waves
- energy is stored in each vibrating particle
- amplitude varies
- all points between consecutive nodes have a constant phase relationship
Equation for velocity in standing wave in string
V^2= T/U
V= velocity
T=tension
U= mass per unit length
Equation for frequency in standing wave in string (learn)
f =1/wavelength x route(T/U)
Refractive index
The ratio of the change in speed from medium 1 to medium 2
Snells law (learn)
n= sin(I)/sin(r)
Critical angle
When the angle of incidence has an angle of refraction of 90° (travels along the boundary)
Equation for critical angle
SinC = n2/n1
SinC = 1/n1
Uses for total internal reflection
Binoculars and fibre optic cables
Converging lens
Where the light rays refract and meet at a focal point
Diverging lens
Where the light rats refract away from each other
Where is the focal point with a diverging lens
There is a virtual focal point in front of the lens
Focal length
The distance from the centre of the lens to the focal point
Equation for power of a lens
Power = 1/focal length
What happens to the power of lenses when they are combined
Pt= P1 + P2 + P3
The lens equation
1/f = 1/u + 1/v
f = focal length u= distance of ray before lens v= distance of ray after lens
Equation for magnification
Magnification = height of image/ height of object
What happens if you get a negative focal length
It’s a virtual image
What is plane polarisation
When two sheets of Polaroid can be roared at 90° to each other to block out light
Diffraction
The spreading of waves after they have passed through an aperture
When is diffraction greatest
When the wavelength is the same as the width of the gap
How is the multiple slit diffraction grating pattern observed
The maxima appear where the small coherent waves have superimposed constructively to produce sharply defined lines
Equation for diffraction grating
n x wavelength = d x sin(x)
n= order if maximum d= slit separation x= angle between central max and diffracted max
How can the max number of orders be found
n
Laws of reflection
- angle of incidence= angle of reflection
* the incident ray, reflected ray and the normal all lie in the same plane
Pulse echo technique
When a wave is reflected off a material and the time recorded to work out how far away the material is (used in ultrasound)
What properties do photons exhibit?
Wave and particle properties
Equation showing energy given by each photon
E = hf
h= Plancks constant f= frequency
Photoelectric effect
The emission of electrons from a material when light is shone into its surface
Work function
The minimum amount of energy that electrons need in order to be released from a metal
Einstein’s photoelectric equation
hf= I + KE
h= Plancks constant f= frequency I= work function KE= kinetic energy
Threshold frequency
The minimum frequency required to reach the work function
How can the kinetic energy of photoelectric be found?
By measuring their stopping potential
Equation for stopping potential
eVs= 1/2mv^2
What is the most stable orbit in an emission spectrum
The ground state
Permitted orbitals
Levels on the emission spectrum where the electron is in an excited state
Equation linking momentum and wavelength
Wavelength = h/p
h= Plancks constant p= momentum
How does decreasing the intensity of the incident light on a metal have an affect on the photoelectric effect.
- lower intensity would contain less photons
- less photons absorbed by electrons
- less electrons emitted
Ground state of an atom
Lowest energy state of an electron in an atom
Why are only certain wavelengths of light emitted due to the photoelectric effect?
- electrons gain energy and move up energy levels
- they then fall down energy levels
- the energy change is given out in the form of a photon
- the energy levels are discrete
- the energy of the photon is equal to the change in energy level
- there are only a limited amount of energy differences and only a corresponding set of frequencies/wavelengths
Explain how the fact that electrons have a range of KE up to a specific max is evidence of the particle nature of light.
- particle nature of light has one photon to one electron
- E=hf so energy transfer is limited
- KE=hf-work function does there is a max KE
- if there were waves the energy would build up over time so there would be no max KE
Photon
A discrete package of electromagnetic light energy
What is an energy level
A discrete quantity of energy for an electron in the atom
Why is the KE in the photoelectric equation KEmax
Because some energy may be transferred to the metal rather than the electron
Why, in an electron gun, is the cathode connected to the negative terminal?
Electrons are repelled by the cathode and attracted to the anode
Explain how polarisation can block out light.
- unpolarised light includes oscillations in all directions
- when plane polarised the oscillations of light are in a single plane
- which is perpendicular to direction of energy transfer
- when the second filter is parallel the light is transmitted so can still be seen
- when the second filter is perpendicular the plane polarised light is absorbed so no light is seen
When using pulse echo technique, why are pulses used rather than a continuous beam?
So they can tell which received pulse matches which sent pulse
What is an inverted image?
When the image produced it upside down
What is virtual image
When the image is perceived to be produced on the same side of the lense as the object
What equation is used for image height object height and focal length of a real image
1/f= 1/u +1/v
What equation is used for image height object height and focal length of a virtual image
1/f= 1/u -1/v
What does u, v and f stand for in the equation 1/f= 1/u +1/v
U= object height V= image height F= focal length
