Flashcards
waves
Flashcards do conjunto (74)
- 1What is a progressive wave?An oscillation of particles or fields that carries energy from one place to another without transferring any matter
- 2How do we know that waves carry energy?--electromagnetic waves heat things up
- x-rays and gamma rays knock electrons out of their orbits causing ionisation
-Loud sounds cause large oscillations of air particles which can make things vibrate
-Wave power can be used to generate electricity
Since waves carry energy away, the source loses energy - 3Definition of a cycle?One complete vibration of a wave
- 4Displacement?Direction and distance a point on a wave has moved from its equilibrium position
- 5Amplitude?Maximum magnitude of displacement from position of equilibrium
- 6Wavelength?The length of one whole wave cycle, from crest to crest or trough to trough
- 7Period?Time taken for a whole cycle to complete or pass a given point
- 8Frequency?The numberof cycles per second passing a given point ... 1/time period
- 9Phase?The position of a certain point along a wave cycle
- 10Phase differenceA fraction of a complete cycle between two points on a wave.
- 11What are mechanical waves?Are the oscillations of particles in a physical medium. They cannot trasmit energy in a vacuum. They can either be transverse or longitudinal
- 12What are electromagetic waves?They are vibrating electric and magnetic fields that travel through space without the need of a substance. They are always transverse waves.
- 13Examples of mechanical waves?- sound waves, earthquake P and S waves and waterwaves
- 14Examples of electromagnetic waves-radiowaves, microwaves, infrared, light, UV x-ray and gamma
- 15what are longitudinal waves? Name examplesLongitudinal waves are waves in which the vibration of the particles is parallel to the direction in which the wave travels.
-sound waves, primary seismic waves, compression waves on a slinky - 16What is compression/rarefraction?Compression is when waves on a slinky are closer together
Rarefraction is when they are further appart - 17What are transverse waves?The direction of travel is perpendicular to the direction of energy transfer
-EM waves, secondary seismic waves, waves on a string. - 18Waves that move outward from their source are called progressive(travelling) waves. The two types are transverse and longitudinal:)
- 19What are longitudical waves usually plotted as on a graph? ' transervse wacves?- longitudinal - displacement agaist time (will appear as a transverse wave)
-transverse- can eb either displacement against time or displacement against distance. - 20How is light polarised?By reflection
- 21Why can transverse waves be polarised but longitudinal waves cant?transverse waves- the electric and magrnatic fields vibrate perpendicular to one another whereas longitudinal all tranvel in the same direction.
- 22What is meant by plane polarised light/when all waves are in the same plane as one another. this can be achieved by using a polaroid filter
- 23What happens if unpolarised light is passed through two polaroid filters at 90 degrees to one another?-the transmission light intensity changes. THe filters are said to be crossed when the transmission intensity os at a minimum. It cannot pass through the second filter as the alignement of the molecules in the second filter is 90 degrees to the alignement of the emolecules in the first filter.
- 24What is the plane of polarisation of an electromagnetic wave?- THE PLANE IN WHICH THE ELECRTIC FIELD OSCILATES
- 25How do polaroid sunglasses work?- they reduce the glare of light reflected by water or glass. sUch light is partly polarised when it reflects and so its intensity is reduced using polaroid sunglasses as it eliminates the horizontal plane which causes glare
- 26Why do the ariels for TV and radio have to be lined up?TV signals are polarised by the orientation of the rods in the broadcasting ariel. To receive a strong signal the ariels have to be lined up.
- 27What is the link between freuency and wavelength of a wave?The higher the frequency, the shorter the wavelength
- 28How us a stationary wave formed?When two progressive waves travelling in oposite directions pass through one another
- 29Wat is the fundamental mode of vibrationA single loop that has a node at either end.
- 30What us ab abtinode?A position inbetween nodes with maximum displacement
- 31Main feature of stationary waves?Energy is stored and not transmitted along the wave
- 32How does energy change across a startionary wave?- The amplitude of vibration is zero at the nodes and so no energy s stored at the node.
-The amplitude of vibraton is maximum at thhe antinodes, so there is maximum energy at the antinodes.
Because these are in fixed positions, no energy is transferred along the wave. - 33How does the phase difference between two vibrating particles change?-zero is they are between adjacent nodes or separated by an even number of nodes.
-180 degrees (pi radians) if the two particles are separated by an odd number of nodes. - 34How the frequency of a wave compares with progressive and startionary waves:stationary- all particles vibrate at same frequency apart from at nodes
progressive- all particles vibrate at same frequency- - 35'' amplitudestationary- varies from zero at a node to maximum at antinode
progressive- same for all particles - 36'' phase differencestationary- equal to m(pi) where m is th enumber of nodes between the two particles
progressive- equal to 2(pi)d/ wavelength - 37What are wavefronts?lines at constant phase that represent waves.
- 38How doe the gap width and wavelength effect the amount the waves spread out?- the narrower the gap, the more the waves spread out.
-The larger the wavelength, the more the waves spread out - 39What is the principle of superposition?When two waves meet, the total displacement at a point is equal to is equal to the sum of the individual displacements at that point
- 40What is constructive/ destructive interference/ cancellation/ partial cn=ancellationWhen two points on a wave reinforce on another eg to form a supercrest. Destructive interference when one part of a crest meets a patr of a trough and the amplitude ta that point bepmes less. Cancellation when a crest meets a trough, partial cancellation, waves do not fully cancel out.
- 41Decsribe stationary waves on a rope.- formed if two people send progressive waves from either end. Combine at fixed points along the riope. At each node, the two sets of waves are always 180 degrees out of phase, so they cancel each other out.
- 42Describe destructive interference in a ripple tank.- points of cancellation are created when a crest from one dipper meets a trough from another dipper. These points of cencellation are seen as gaps in the wavefrnts.
- 43What is interferenceWhen cancellation and reinforcement occurS
- 44How doe the displacement and velocity vary for two points that are in phse?They are the same
- 45When are waves considered to be in phase?When they have a wave difference of zero or multiples of 360 degrees
- 46when are waves considered to be exactly out of phase?WHEN THEY ARE 180 DEGREES ( PI RADIANS OR HALF A CYLCE) OUT OF PHASE
- 47How does coherence effet the interference pattern of a waveif they are coherent, you wi ll get fixed patterns of reinforcement and cancellation, if not then the interference will still occur but at irregular intervals
- 48When are sources considered cooherent?If they are of the same wavelength and frequency and there is a fixed phase difference between them.
- 49What is the oath difference?How much further one wave has travelled than another wave to reach a point
- 50What will you observe at a point where two coherent wave sources meet at a point equal distances fro both sources?You will get constructive interference at any point where the difference is a whole number of wavelenths. The points where the path difference is half a wavelength, the waves arrive out of phase and you get destructive interference.
- 51What aree points of minima/maxima and equations?- maxima are at maximum displacement n(lambda)
-minima are points of minimum displacement(zero displacement) nlambda/2 - 52What are the conditions needed to produce a stationary wave on a string?There must be a node at either end of the string
- 53What isi the fundamental pattern of vibration?Lowest possible frequency that gives a patters. Antinode at the middle and a node at either end
- 54What is the wavelength thaht produces this pattern?2L where L is the position from node to node
- 55What does the pitch of anote corespond to ? How can this factor be altered to adjust the pitch?-frequency
-increasing the tension of the string will shorten its length and increase the pitch etc... - 56explain why it is important to correctly align the aerial of TV in order to receive the strongest signalften polarised, aerial must be aligned in the same plane of the electric field of the wave
- 57A continuouse wave of the same amplitide and frequency moves along the rope from the right and passes through the first wave. The know becomes motionless. Explain how.(1)- it would become a node
(1) as thhe waves are coherent and so cancellation occurs
(1) a stationary wave is formed by inteference - 58Describe the key featires of a stationary wave- formed when two coherent waves travelling in opposite directions pass through one another
-Nodes are at 0 displacement
-Abtidones are at maximum displacement
-there is no energy transfer in a stationary wave - 59describe the motion of a point in a stationary waveIt oscillates/vibrates repeatedly about equilibrium
- 60State the physical conditions that are necessary for a stationary wave to form on the string-- must be a node at either end
- the reflection must have similar amplitude and frequency
- the reflected wave loses only a little energy - 61OPTICS:/:(
- 62WHat is refraction?change of direction that occus when light passes non-normally across a boundary between two transparent substances with different optical densities
- 63which way does the light ray bend if it travels into a more/ less dense substace-towards the normal in a more dense substance
-away from the normal in a ess dense substance - 64relationship between angle of refractin and incidence?angle of refraction is always less than the angle of incidence
- 65what is snells law?-the ratio of sin i/sin r is the same for each light ray through a particular material. The ratio is referred to as the refractive index of the substance
- 66What is the angle of refraction emerging from a glass block equal to?the angle of incidence of the light ray entering the block
- 67why is this so?because the two sides of the bock are parallel to one another
- 68how is the equation sin i2/ sinr2= 1/n derivedi2=r1
r2-i1 - 69What is the critical angle?the angle where the rafracted ray is at 90 degrees and emerges along the boundary
- 70What haooens if the angle is smaller/ larger tan the critical anglesmaller- refraction and partial reflection
larger- total internal reflection - 71two requirements for total internal reflection to take place?- ange must be larger than the critical angle
-the incident substance must have a larger refractive index than the other substance - 72when does partial internal reflection occur?when the angle of incidence is less than or equal to the critical angle
- 73why does a diamond sparkle?It has a high refractive index and so separetes the colours more than any other substance does. It has a low critical angle and so light may undergo total internal reflection many times befroe it eaves the diamond which meanst the colours spread out more and so sparkle
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- FlashCards sobre waves, criado por 12deebleabigail em 20-04-2016.
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