Waves Flashcards
What is a progressive wave?
A progressive wave transfers energy without transferring material and is made up of particles of a medium oscillating
Example: Water waves are made of water particles moving up and down.
Define amplitude in the context of waves.
A wave’s maximum displacement from the equilibrium position (units are m)
Amplitude indicates the energy of the wave.
What does frequency (f) measure?
The number of complete oscillations passing through a point per second (units are Hz)
Frequency is inversely related to the period.
What is wavelength (λ)?
The length of one whole oscillation (e.g. the distance between successive peaks/troughs) (units are m)
Wavelength is related to the energy and frequency of a wave.
What is the formula for wave speed (c)?
c = fλ
Where c is speed, f is frequency, and λ is wavelength.
How is frequency related to the period (T)?
f = 1/T
Frequency is the reciprocal of the period.
What are transverse waves?
Waves where the oscillation of particles is at right angles to the direction of energy transfer
All electromagnetic (EM) waves are transverse.
What is an example of a longitudinal wave?
Sound
Longitudinal waves consist of compressions and rarefactions.
What is polarisation in waves?
A polarised wave oscillates in only one plane; only transverse waves can be polarised
Polarisation is evidence for the nature of transverse waves.
What is constructive interference?
Occurs when two waves have displacement in the same direction
This leads to a resultant wave with increased amplitude.
What is destructive interference?
Occurs when one wave has positive displacement and the other has negative displacement
Total destructive interference occurs if the waves have equal but opposite displacements.
What is a stationary wave?
Formed from the superposition of two progressive waves traveling in opposite directions with the same frequency, wavelength, and amplitude
No energy is transferred by a stationary wave.
What are nodes and antinodes in stationary waves?
Nodes are regions of no displacement; antinodes are regions of maximum amplitude
Nodes occur where destructive interference occurs, and antinodes occur where constructive interference occurs.
What is Young’s double slit experiment used to demonstrate?
Interference of light from two coherent sources
It showcases the wave nature of light.
What is diffraction?
The spreading out of waves when they pass through or around a gap
Greatest diffraction occurs when the gap is the same size as the wavelength.
What is a diffraction grating?
A slide containing many equally spaced slits very close together
Produces sharper and brighter interference patterns than a double slit.
What does the refractive index (n) measure?
How much a material slows down light
It is defined as the ratio of the speed of light in vacuum to the speed of light in the material.
Fill in the blank: The distance between adjacent nodes (or antinodes) is _______.
half a wavelength
This applies to any harmonic.
True or False: Sound waves can travel in a vacuum.
False
Longitudinal waves, like sound, require a medium to travel.
What happens to the intensity of diffraction fringes as you move away from the central maximum?
The intensity decreases
Bright fringes are caused by constructive interference.
What is the first harmonic in stationary waves?
The lowest frequency at which a stationary wave forms with two nodes and a single antinode
The frequency can be calculated using specific formulas.
What is X-ray crystallography?
A technique where x-rays are directed at a thin crystal sheet to form a diffraction pattern, used to measure atomic spacing in certain materials.
Define refractive index (n)
A property of a material measuring how much it slows down light, calculated by dividing the speed of light in a vacuum (c) by the speed of light in that substance (cs).
What does a higher refractive index indicate?
It indicates that the material is more optically dense.
What is the refractive index of air approximately equal to?
Approximately 1.
What occurs during refraction?
A wave changes direction when entering a different medium, depending on the refractive index.
What is Snell’s Law?
n1 sinθ1 = n2 sinθ2, where n1 and n2 are the refractive indexes of materials and θ1 and θ2 are the angles of incidence and refraction.
What happens when light moves from a less optically dense to a more optically dense medium?
The ray of light slows down and bends towards the normal.
What is the critical angle (θc)?
The angle of incidence when the angle of refraction reaches 90°.
What is total internal reflection (TIR)?
An effect that occurs when the angle of incidence is greater than the critical angle and the incident refractive index is greater than the refractive index of the boundary.
What are optical fibres used for?
They carry information in the form of light signals.
What materials make up an optical fibre?
An optically dense core surrounded by cladding with a lower optical density.
What causes signal degradation in optical fibres?
Absorption and dispersion.
What is absorption in the context of optical fibres?
When part of the signal’s energy is absorbed by the fibre, reducing the amplitude of the signal.
What is modal dispersion?
Caused by light rays entering the fibre at different angles, leading to different path lengths and pulse broadening.
How can modal dispersion be reduced?
By making the core of the optical fibre very narrow.
What is material dispersion?
Caused by using light of different wavelengths, leading to pulse broadening due to varying speeds.
How can material dispersion be prevented?
By using monochromatic light.
What is an optical fibre repeater used for?
To regenerate the signal during its travel to its destination.
What is amplitude in relation to waves?
A wave’s maximum displacement from its equilibrium position.
Define antinode.
A position of maximum displacement in a stationary wave.
What is cladding in optical fibres?
A protective layer that improves tensile strength, prevents scratching, and avoids signal transfer between adjacent fibres.
What does coherence in waves mean?
Waves are coherent if they have the same wavelength and frequency and a fixed phase difference.
What is a diffraction grating?
A grating with hundreds of slits per millimetre that results in sharper interference patterns.
Define diffraction.
The spreading of waves as they pass through a gap of a similar magnitude to their wavelength.
What are electromagnetic waves?
Waves that consist of perpendicular electric and magnetic oscillations.
What is frequency in wave terms?
The number of waves that pass a point in a unit time period; the inverse of the time period.
Define fringe spacing.
The distance between two adjacent bright or dark fringes.
What is interference?
The superposition of waves when two waves meet, resulting in constructive or destructive interference.
What is a laser?
A light source that produces a collimated and coherent beam.
What is a longitudinal wave?
A wave with oscillations that are parallel to the direction of energy propagation.
What is node in wave terminology?
A position of minimum displacement in a stationary wave.
What is an optical fibre?
A thin glass fibre through which signals are passed, usually surrounded by cladding.
Define path difference.
A measure of how far ahead a wave is compared to another wave, expressed in terms of wavelength.
What is phase difference?
The difference in phase between two points on a wave, usually expressed in radians.
What does phase measure?
How far through the wave’s cycle a given point on the wave is.
What is polarisation?
The restriction of a wave so that it can only oscillate in a single plane.
What is pulse broadening?
The elongation of a signal passed down an optical fibre due to modal or material dispersion.
What is the formula for refractive index?
n = c / cs, where c is the speed of light in a vacuum and cs is the speed in the material.
What does Snell’s Law relate to?
It links a wave’s angle of incidence to its angle of refraction using the refractive indexes of the mediums involved.
What is speed in wave terms?
The product of a wave’s frequency and wavelength.
What is a stationary wave?
A wave that stores, but does not transfer, energy.
What is total internal reflection?
An effect where full reflection occurs at the inside boundary of an optical fibre, preventing radiation from passing out.
What characterizes a transverse wave?
A wave with oscillations that are perpendicular to the direction of energy propagation.
Define wavelength.
The distance between two identical positions on adjacent waves, commonly measured from peak to peak or trough to trough.
What does Young’s Double-Slit Experiment demonstrate?
The diffraction of light by passing monochromatic light across two narrow slits.
