Flashcards in Vibrations Deck (37):
What does a progressive wave do?
Carries energy from one place to another without transferring any material.
What is a mechanical wave?
A wave that passes through a substance.
What are waves caused by?
• Wave is caused by something making particles or fields oscillate at a source.
• These oscillations pass through the medium as the wave travels, carrying energy with it
What happens to the particles of a substance when a wave passes through it?
• When waves pass through a substance, the particles of the the substances vibrate in a way which makes the nearby particles vibrate in the same way.
What are electromagnetic waves?
• Oscillating electric and magnetic fields that progress through space without the need for a substance.
• The vibrating electric field generates a vibrating magnetic field, which generates a vibrating electric field further away, and so on.
How can you tell that waves carry energy?
• Electromagnetic waves cause things to heat 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 of the wave loses energy.
What is a cycle?
One complete vibration of the wave
What is displacement?
How far a point on the wave has moved from its undisturbed position.
What is amplitude?
Maximum magnitude of displacement
What is wavelength?
The length of one whole wave cycle, from crest to crest, or trough to trough.
What is the period?
Time taken for a whole cycle to complete, or pass a given point.
What is the frequency?
The number of cycles per second passing a given point.
What is a phase?
Measurement of the position of a certain point along the wave cycle
What is the phase difference?
The amount one wave lags behind another.
What are phase/phase difference measured in?
• Fractions of a cycle.
What is reflection?
When the wave is bounced back when it hits a boundary
What is refraction?
• The wave changes direction, as it enters a different medium.
• The change in direction si a result of the wave slowing down or speeding up.
What is the formula for frequency?
1 / Period
What is the formula for wave speed?
Distance travelled / Time taken
What is the formula for the speed of a wave?
Wavelength x Frequency
What are longitudinal waves?
Waves in which the direction of vibrations of the particles is parallel to the direction in which the wave travels.
What are some examples of longitudinal waves?
• Sound waves.
• Seismic Waves
What does a longitudinal waves consist of?
• Compression and rare fractions of the medium it is travelling through.
• For this fact, they also cannot travel through space without a medium.
What are transverse waves?
Waves in which the direction of vibration is perpendicular to the direction in which the wave travels.
What are some examples of transverse waves/
• Electromagnetic waves.
What does it mean for a wave to be plane pol;polarised?
Waves can be plane polarised if the vibrations stay in one plane only.
What does it mean if the vibrations are un-polarised?
They change from one plane to another.
What type of waves can be polarised?
• Transverse Waves
• Longitudinal waves cannot be plane polarised.
What happens if waves pass through Polaroid filters?
When they pass through the polarising filter, they become polarised because only the vibrations parallel to the slit can pass through it.
What does it mean when the filters are crossed?
Two Polarised Filters
• Polarised light from the first filter cannot pass through the second filter, because the alignment of molecules in the second filter is at 90 degrees to the alignment in the first filter, resulting in minimum intensity.
What spectrum is light a part of?
Light is a part of the spectrum of electromagnetic waves.
What is the plane of polarisation of an electromagnetic wave?
The plane in which the electric field oscillates.
What do Polaroid glasses do?
• Reduce the glare of light reflected by water or glass.
• The reflected light is polarised and the intensity is reduced when it passes through the Polaroid sunglasses.
How can waves be polarised?
Using a polarising filter.
What happens if you have two polarising filters at right angles to each other?
No light will get through.
What happens to TV signals?
•They are polarised by the orientation of the rods on the broadcasting aerial, with the rods on the transmitting aerial.
• If they aren't aligned the signal strength will be lower.