Waves Flashcards
(35 cards)
Define frequency and give its units.
The number of waves passing through a point per second. (hertz) Hz
Define wavelength.
shortest distance between two points in phase
Define amplitude.
The maximum displacement of the wave from its equilibrium position.
What is a longitudinal wave?
A wave in which the oscillation of the particles is parallel to the direction of energy transfer. There are rarefactions (areas of low pressure) and compressions (areas of high pressure).
What is a transverse wave? Give examples.
Waves where the particle oscillations are perpendicular to the direction of energy transfer.
For example: electromagnetic waves
True or False? The magnetic field and electric field in a electromagnetic wave are parallel to each other.
False.
The electric and magnetic field are at right angles to each other
What does a polarising filter do?
Only allows oscillations in one plane.
How is polarisation used as evidence of the nature of transverse waves?
Polarisation can only occur if a wave’s oscillations are perpendicular to its direction of travel (as they are in transverse waves).
How are polarisers used in antennas?
TV and radio signals are usually
plane-polarised by the orientation of the rods on the transmitting aerial, so the receiving aerial must be aligned in the same plane of polarisation to receive the signal at full strength.
What is a stationary wave?
superposition of two progressive waves with the same frequency, wavelength and amplitude, moving in the opposite direction
transfers no energy
positions of maximum and minimum amplitude are constant
What is a node?
Where the waves meet completely out of phase, total destructive interreference occurs and regions of zero displacement form.
What is an antinode?
Where the waves meet in phase, constructive interference occurs so regions of maximum amplitude form.
Define coherence.
Waves are said to be coherent if they have:
The same frequency
A constant phase difference
Why is a laser useful in showing interference and diffraction?
It produces monochromatic (same wavelength / colour) light so diffraction and interference patterns are more defined.
What was Young’s double-slit experiment?
A single light source is directed towards two slits, which each act as a coherent light source, the light interferes constructively and destructively to create an interference pattern
Describe the interference pattern created using white light.
A bright white central maximum flanked by alternating spectral fringes of decreasing intensity with violet closest to the zero order and red furthest
Why does an interference pattern form when light is passed through a single slit?
The light diffracts as it passes through the slit, where the waves are in phase constructive interference occurs making bright fringes and where the waves are completely out of phase destructive interference occurs making a dark fringe
Increasing the slit width increases the width of the central diffraction maximum. True or False?
False, the slit is not so close to the wavelength in size so less diffraction occurs - the central maximum becomes narrower and more intense
When light enters a more optically dense medium does it bend towards or away from the normal?
Towards the normal.
When does total internal reflection occur?
When light is at a boundary to a less optically dense medium and the angle of incidence is greater than the critical angle.
What is the purpose of the cladding in a step index optical fibre?
● Protects core from scratches which would allow light to escape and degrade the signal.
● Allows TIR as it has a lower refractive index than the core.
How does signal degradation by absorption in an optical fibre affect the received signal?
Part of the signal’s energy is absorbed by the fibre so its amplitude is reduced.
What is pulse broadening?
When the received signal is wider than the original, this can cause overlap of signals leading to information loss.
How does modal dispersion cause pulse broadening?
Light rays enter the fibre at different angles so they take different paths along it, some may travel down the middle while others are reflected repeatedly, so the rays take different times to travel along the fibre, causing pulse broadening.
