physics - waves Flashcards
what are the 2 types of waves
mechanical and electromagnetic waves
what is the definition of a mechanical waves and give examples
a mechanical wave needs a medium.
examples : waves on a guitar string , water waves , seismic waves.
what is the definition of an electromagnetic waves and give exampled
the electromagnetic wave does not need a medium.
examples : radio waves , infrared , ultraviolet.
what is the definition of a longitudinal wave ?
in a longitudinal wave the oscillations of the particles are parallel to the direction in which the wave travels.
what is the definition of a transverse wave ?
in a transverse wave the oscillations of the particles are perpendicular to the direction in which the wave travels.
give some examples of a longitudinal wave ?
sound
give some examples of a transverse waves ?
radio waves
microwaves
water waves
mexican wave
what is the definition of frequency ?
frequency is the number of waves that pass a point each second.
what is the definition of periodic time ?
the periodic time is the time taken for 1 whole oscillation.
what is the wave speed equation ?
wave speed = frequency x wavelength.
(m/s) (Hz) (m)
what is the definition of diffraction ?
diffraction is the way that waves spread out as they come through a narrow gap or go around obstacles.
when does diffraction occur ?
diffraction occurs when waves pass through gaps.
when does diffraction work best ?
diffraction works best if the wavelength of the gap is longer or narrower.
key fact about diffraction
if the gap is too large most of energy gets through , but most of waves pass straight through so diffraction is ineffective.
how can we hear around corners but not see around corners ?
light has a much smaller wavelength than the width of the doorway so there is little diffraction. the wavelength of sound is closer to the width of the doorway so there is more diffraction.
describe how a longitudinal wave travels through air ?
the particles oscillate parallel to the direction in which the wave moves, through a series of rarefactions and compressions in the air .
what is the definition of displacement ?
displacement is the distance from the equilibrium position.
what is the definition for amplitude of a wave ?
the amplitude of a wave is the height of the wave form the middle to a peak or trough.
what is constructive interference ?
constructive interference is when the crests or troughs of 2 waves coincide , they combine to create an amplified wave . the two waves are in phase with each other , there is 0 phase difference between them.
what is destructive interference ?
destructive interference is where the crests of 1 wave are aligned with the troughs of another, they cancel each other out . the waves are out of phase or interphase with each other.
what is the definition of superposition
superposition is the adding together of wave displacements that occurs when two separate sources overlap. the displacements add mathematically.
what is phase difference ?
phase difference is when 2 points which are always moving in the same direction are said to be in phase.2 points a whole wavelength apart are in phase.
what is antiphase
two points which are always moving in the opposite direction are said to be in antiphase. two points half a wavelength apart are in antiphase.
describe what is meant by
coherence
waves are coherent of they have the same frequency and wavelength and a constant phase relationship.
what is diffraction Grating ?
a diffraction grating has many lines close together.
key facts about diffraction grating
the gaps in the grating are close to the wavelength of light. the rays of light will diffract when they go through the gaps.
describe and explain what is produced when monochromatic light is shone on a diffraction grating ?
we would see a series of bright spots with dark areas in between. monochromatic light contains only 1 wavelength .when lights passes through slits in the diffraction grating it spreads out. the light waves overlap and interfere. at points where 1 wave has travelled a whole number of wavelengths further than the wave next to it they interfere constructively and we get a maximum. at points where 1 wave has travelled half a wavelength further than the wave next to it they interfere destructively and we get a minimum.
definition of progressive waves ?
progressive waves are when waves travel, transferring energy from one position to another.
definition of stationary waves ?
stationary waves are made from 2 coherent waves travelling in opposite directions.
definition of a node
a node is a point that always has zero amplitude , caused by destructive interference.
definition of an antinode ?
an antinode is a point of maximum amplitude , caused by constructive interference - half way between two nodes.
how do musical instruments work ?
musical instruments work by producing resonance.
what is the definition of Resonance
resonance is the storing of energy in a stationary wave.
how is the mass per length calculated ?
mass per unit length = mass / length
give 3 ways in which the note produced by a guitar can be altered ?
putting pressure on the string
plucking the string
palm muting.
key fact about wind instruments
wind instruments work by creating a standing wave inside the cylinder of the instrument . they are resonators.
Compare the types of wave formed on a guitar string and formed in a recorder when musical notes are produced.
Both made by vibrations . Both use resonance . Both form standing waves. In the guitar a string vibrates, in the recorder air vibrates. In the guitar string there’s a transverse wave, in the recorder there’s a longitudinal wave. Guitar sting has nodes at both ends, recorder has antinodes and each end The pitch of the note from a guitar string can be changed by changing the length, thickness or tension in the string. The pitch of the note from a recorder can be changed by changing the length of the pipe.
key fact about standing waves in an aerial
TV antenna’s have a reflector at the back which bounces incoming waves back and creates a stationary wave pattern. The detectors are places at the antinode positions.
key fact about standing waves in microwaves.
Stationary wave patterns are caused by reflections of microwaves off the metal walls of the oven. Hot spots are occur in the antinodes and the cold spots occur in the nodes. This is why the turntable rotates.
key fact about string theory
Electrons behave like stationary waves as they bounce around in each energy level. The energy levels electrons occupy represent a stationary wave pattern. Patterns with high numbers of nodes represent a higher energy level.
what is the order of the electromagnetic spectrum ?
radio waves , microwaves , infra red radiation , visible light , ultraviolet light , x rays , gamma rays
what 2 waves of the electromagnetic spectrum have the longest wavelength but the lowest frequency
Radio waves and microwaves.
what 2 waves of the electromagnetic spectrum have the shortest wavelength but the highest frequency
x - rays and gamma rays.
