Topic 05: Waves and Particle Nature of Light Flashcards
Absorption spectrum
The frequencies at which a certain element absorbs photons at a higher rate as these frequencies correspond to the spacings between energy levels in the element’s atoms
Amplitude
The maximum displacement of a vibrating particle or wave from its equilibrium position
Angle of incidence
The angle at which a light ray hits a medium. Measured from a line perpendicular to the surface of the medium
Angle of reflection
The angle at which a light ray reflects off a surface. Measured from a line perpendicular to the surface of the medium
Angle of refraction
The angle at which light rays travel after transferring into a different refractive index material. Measured from a line perpendicular to the surface of the medium
Antinode
The point on a stationary wave where the incoming and reflected wave are in phase forming a maximum point
Coherence
Waves with the same frequency and constant phase difference
Constructive interference
Interference when the two waves are in phase. If the two waves are both at their peak, the addition of the two peaks become large
Critical angle
A lens that takes a parallel set of light rays and causes them to meet at a point
De Broglie hypothesis
All particles have a wave-like nature and a particle-like nature. The wavelength of a particle is inversely proportional to the particle’s momentum
De-excitation
The movement of an electron from a high-energy level to a lower energy level. This occurs in excited atoms over time and causes photons to be released
Destructive interference
Interference when the two waves are in antiphase. When one wave is at a peak and one is at a trough, their addition results in a minimum point
Diffraction
The spread of a wave as it passes through a gap or over an edge
Displacement
The distance and direction that a vibrating particle or wave has travelled from its equilibrium position
Diverging lens
A lens that takes a parallel set of light rays and causes them to travel away from each other and not meet
Electronvolt
The kinetic energy gained by one electron that is accelerated through a potential difference of 1 volt. Equal to 1.6×10^(−16) J
Emission spectrum
When a certain element’s atoms de-excite they move from one energy level to another with a specific energy gap between these levels. This creates a photon of that specific energy at it is the frequencies of these photos that make up the emission spectrum
Excitation
The movement of an electron from a low energy level to a higher energy level. This occurs when an other electron or photon transfers energy to an orbital electron, causing it to move to a higher energy level
Focal length
The distance from the centre of the lens to the focal point
Focal point
The point at which rays of light passing through a lens converge (or appear to converge)
Frequency
The number of complete oscillations of a wave (wave cycles) per second
Fundamental frequency
The oscillations of an entire object forming the lowest possible frequency for that object. For a string fixed at both ends, this is where there is only a single antinode in the middle of the string
Huygen’s principle
Every point on a wavefront can be treated as the point source of a secondary wavelet
Ionisation
When an electron is removed from an atom, giving the atom a positive charge
In antiphase
When the phase difference between two waves is 180 degrees or π radians
In phase
When the phase difference between two waves is 0 degrees or 0 radians
Intensity
The power transferred by a wave per unit area
Lens power
The inverse of the focal length
Longitudinal wave
A wave whose oscillations are parallel to the direction of propagation of the wave (e.g. sound waves)
Magnification
The height of an object divided by the height of its image
Node
The point on a stationary wave where the incoming and reflected wave are in antiphase, forming a minimum point
One-to-one interaction
When one photon transfers all of its energy to a single electron in a photoelectric process
Path difference
For two waves starting from different points and arriving at the same point, the path difference is the difference in the length travelled by each wave, measured in metres
Period
The time taken for a wave to complete one full cycle
Phase
If the full cycle of a wave (peak to peak) is represented on a circle with the first peak at 0° (0 radians), the trough at 180° (π radians) and the next peak at 360° (2π radians), the phase is where on that circle the wave is at a given point in space and time. Measured in radians or degrees
Phase difference
The difference in phase if the phase of the two waves is determined at a single point in time, measured in radians or degrees. It can be seen as the amount by which one wave lags behind another
Photoelectric effect
When light of a high enough energy shone on a metal surface causes electrons to be emitted. The electrons are given enough kinetic energy by the photons to overcome the attractive force of the ions in the metal
Polarised wave
A wave whose oscillations have been restricted to the same plane
Principal axis
A passing through the centre of the lens. Passing through the axis of the lens where it is thinnest
Progressive wave
A wave that transfers energy from one point to another
Pulse-echo technique
An ultrasound technique used for imaging of objects, notably in medical imaging. Short pulses of ultrasound are sent through a medium and their reflections recorded
Real image
Where rays of light have actually converged to produce an image and can be projected onto a screen
Refraction
When a wave changes speed when it crosses the boundary into a new medium
Refractive index
A measure of how much the speed of light changes between two different media. If one media is a vacuum, then the absolute refractive index is found. For two different non-vacuum materials, the relative refractive index is found
Snell’s law
The relative refractive index can be found from the ratio of the sines of the angles of incidence and refraction
Snell’s law
The relative refractive index can be found from the ratio of the sines of the angles of incidence and refraction
Stationary wave
A wave that stores energy instead of transferring it. A common example is a string fixed at both ends. They are formed by a wave propagating and being reflected so that it comes into superposition with itself
Stationary wave
A wave that stores energy instead of transferring it. A common example is a string fixed at both ends. They are formed by a wave propagating and being reflected so that it comes into superposition with itself
Superposition
When two waves meet at the same point in space, their displacements combine and the total displacement at that point becomes the sum of the individual displacements at that point. Also referred to as interference
Threshold frequency
The minimum frequency of light needed to cause electrons to be emitted in the intensity
Total internal reflection
When the angle of incidence is greater than the critical angle and the ray reflects at the surface and remains within the medium
Transverse wave
A wave whose oscillations are perpendicular to the propagation of the wave (e.g. electromagnetic waves)
Ultrasound
Sound waves with a frequency greater than 20 kHz
Virtual image
When rays of light only appear to have converged and cannot be projected onto a screen
Wavefront
The surface made up of all the points of the wave that are in phase with each other
Wavelength
The distance between two identical points on a wave. Typically measured peak to peak or trough to trough
Wave speed
The distance travelled by a wave per second. The product of the frequency and the wavelength. For an electromagnetic wave in a vacuum, this is always equal to c (3×10^8 ms^(-1))
Work function
The minimum energy required to just liberate an electron from the surface of a metal
