Waves and the Particle Nature of Light Flashcards
What is a wave?
A periodic disturbance in a material or space which transfers energy
Frequency Definition
Number of waves passing a point per second
Amplitude Definition
Maximum displacement of a wave
Wavelength Definition
Distance covered by a full cycle of a wave
Time Period Definition
Time taken for one complete oscillation
Coherent Definition
Two waves with the same wavelength and frequency with a constant phase difference.
What is the frequency equation?
Frequency (Hz) = 1 / Time Period (s)
What is the wave speed equation?
Wave speed (ms^-1) = Frequency (Hz) x Wavelength (m)
What is the intensity equation?
Intensity (Wm^-2) = Power (W) / Area (m^-2)
What are longitudinal waves?
Oscillations parallel to the direction of energy transfer, made up of compressions and rarefractions that are transmitted through a medium (e.g. sound)
What is the speed of sound?
330 ms^-1
What is a transverse wave?
Oscillations perpendicular to the direction of energy transfer
What is the wavelength of visible light?
4 to 7 x 10^-7
What is the speed of light?
300000000 ms^-1
What is a standing wave?
Standing waves are created by the superposition of two progressive waves of equal frequency and amplitude moving in opposite directions causing energy to be stored.
What is a node?
A node is a point on a standing wave where destructive interference occurs as waves are anti - phase so it is a point of zero displacement.
What is an anti-node?
An anti-node is a point on a standing wave where constructive interference occurs as waves are in phase so it is a point of maximum displacement.
What is the speed of a transverse wave on a string equation?
Speed (ms^-1) = Square root of Tension (N) / mass per unit length (kgm)
What is superposition?
When two or more waves meet at a pint and there resultant displacements sum together
What is interference?
Outcome of a combination of waves through superposition
What is constructive interference?
In phase waves meet at a point and sum to create a amplitude of maximum displacement (antinode)
What is destructive interference?
When two waves which are anti phase meet and there resultant amplitude is zero (node)
What is meant by anti-phase?
When the phase difference is 180 degrees
What is meant by in phase?
When there is no phase difference between the two waves.
What is a phase difference?
The difference between the position of two waves oscillating in the same direction, measured in degrees or radians
What is path difference?
The difference between the distance that two waves must travel from their sources to a given point measured in metres
How do you convert from degrees to radians?
Degrees x Pi/180
What is the name of a standing waves frequency?
Resonant Frequency
What is a resonant frequency?
A resonant frequency is when the distance between two fixed ends is an integer multiple of a half wavelength.
What is a focal point?
The point where the light waves diverge / converge to form an image.
What is the focal length?
Distance between the focal point and lens.
What is the lens formula?
1/focal length = 1/object distance + 1/image distance
What does it mean if the image distance is negative?
It’s a virtual image
What does it mean if the focal length is negative?
It’s a diverging lens
What is the magnification equation?
Magnification = Image Height or Distance / Object Height or Distance
How do you calculate the total magnification of several lenses?
It is the product of all the magnifications.
What is lens power?
Lens power is the inverse of the focal length, and a measure of how much it will converge/diverge light.
What is the Lens Power equation?
Lens Power (Dioptres/m^-1) = 1/Focal Length (m)
How can you tell what type of lens it is from lens power equation?
Converging is positive and diverging is negative.
How do you calculate the total lens power?
It is the sum of each lenses power.
What are convex lenses?
Convex Lenses cause light rays to converge together.
What are concave lenses?
Concave lenses cause light rays to diverge together.
What properties can the image from a lens have?
It can be real or virtual, diminished or magnified and upright or inverted.
What is meant by a real image?
An image that can be formed on a screen because light passes through the image.
What is meant be a virtual image?
An image that appears to come from behind the lens.
What is the law of reflection?
The angle of incidence ray is equal to the angle of reflected ray on a smooth surface.
What is refraction?
When a ray of light at an angle to the normal changes direction when it passes from one medium to another due to a change in wave speed.
What is a wavefront?
A line or surface in a wave along which all points are in phase.
What happens to a wave as it enters a denser medium?
The wave slows down and bends towards the normal.
What happens to a wave as it enters a less dense medium?
The wave speeds up and bends away from the normal.
What are the average refractive indexes of air, water and glass.
1, 1.33 and 1.5
What is Snell’s Law?
Snell’s law states that the refractive index for a wave travelling from one medium to another is given by the equation: n1sinx1 = n2 sinx2
How do you calculate the refractive index of a material?
Refractive Index = Speed of light in a vacuum (3 x 10^8) / Speed of light in material
What is total internal reflection?
When light goes from a high to low refractive index material and the angle of incidence becomes larger than the critical angle causing light to be internally reflected and no light leaves the object.
What is the critical angle?
The angle of incidence for which the angle of refraction is 90 degrees
What is the equation to find the critical angle?
n1 sin(C) = n2
What is diffraction?
When a wave passes through a gap or is partially obstructed by a barrier so the wave front spreads out>
What happens when the wavefront is the same size as the wavelength?
The wave front does not diffract very much however the smaller the gap or larger the wavelength the more diffraction will occur.
What is Huygens Principle?
Every point on a wavefront of a progressive wave can be a source of circular waves moving forward from that point and the resultant wavefront is found from the superposition of these waves.
What happens in constructive interference during diffraction?
Bright spots will form as the path difference is an integer wavelength and are in phase.
What happens in destructive interference during diffraction?
Dark spots will form as the path difference is not an integer number and waves are anti phase.
What is a diffraction grating?
A diffraction grating disperses light of different wavelengths into light components by wavelength.
How is white light dispersed in a diffraction grating?
The red light is found on the outer part as it has the longest wavelength and the blue in the middle as it has the shortest wavelength.
How do you find the diffraction grating?
d (metres) = 1 / Lines per m or 1 x 10^-3 / Lines per mm
What equation is used to calculate the wavelength from the angle of central to diffracted maxima?
nλ = dsinx or order of maxima x wavelength of incident radiation = spacing between lines of grating x sin(angle from centre)
What is polarised light?
A transverse waves oscillations are in one plane only including the direction of energy transfer (horizontal or vertical)/
What are examples of polarisers?
Sunglasses, TV Aerials, 3D Glasses
What is the intensity equation?
Intensity (Wm^2) = Power (W0 / Area (m^2)
What is the photoelectric effect?
When one photon from light interacts with one electron on the surface of the metal. Electron is released if energy of the photon is greater than the work function so it can escape the attraction of the nucleus. Or frequency is greater than threshold frequency. Electrons liberated are called photoelectrons.
What is a photon?
A discrete package of energy of EM radiation.
Photoelectric Effect Energy Equation
Energy Supplied = Plancks Constant x Frequency
Or
Energy Supplied = (Plancks Constant x Speed of Light) / Wavelength
What is work function?
Minimum energy of photon for an electron to be liberated from the surface of a metal
What is threshold frequency?
Minimum frequency of a photon for photoelectric effect to occur
Work Function Equation
Work Function = Plancks Constant x Threshold Frequency
How do you convert between ev and joules?
1ev = 1.60 x 10^-19
What happens if the photon has more energy than work function?
The excess energy is given to the electron as kinetic energy so
E = hf = Work Function + 1/2mv^2
What is the atomic spectra?
Electrons get excited and move to a higher energy level. The electron then falls back down to a lower energy level and releases a photon. However only certain energy levels are possible so energy of photon must equal the difference in energy levels.
What is the atomic spectra equation?
hf = E1 - E2
Why can atomic spectra only take place at certain frequencies?
As there are certain energy level the electron can move between and as E = hf
only corresponding frequencies of a photon will allow the atomic spectra to occur.
What is wave particle duality?
Light can be a wave as proven by diffraction but can also be a particle as proven by the photoelectric effect.
What is De Brogiles Equation?
Wavelength = Plancks Constant / Momentum
What is De Brogiles Equation used for?
To determine the wavelength of an electron undergoing electron diffraction.
