4.1- WAVES AND VIBRATIONS Flashcards
What are waves that pass through a substance?
vibrations which pass through that substance
How are sound waves in air created?
by making surface vibrate so it sends compression waves through the surrounding air
Examples of waves that pass through a substance (3)
sound waves
seismic waves
waves on strings
What are sound waves, seismic waves and waves on strings referred to as?
mechanical waves
What are mechanical waves?
when waves progress through a substance, particles of substance vibrate in certain way which makes nearby particles vibrate in same way, and so on
What are electromagnetic waves?
oscillating electric and magnetic fields that progress through space without need for a substance
What does the vibrating electric field of an EM wave generate?
a vibrating magnetic field
What does the vibrating magnetic field of an EM wave generate?
a vibrating electric field
What are the EM waves
radio waves microwaves infrared radiation visible light UV radiation X-rays gamma radiation
What are longitudinal waves?
waves in which the direction of vibration of particles is parallel to direction in which wave travels
Examples of longitudinal waves? (3)
sound waves
primary seismic waves compression waves
What happens when one side of a slinky is moved to and fro repeatedly?
each “forward” movement causes a compression wave to pass along the slinky as the coils push into each other
What does the “reverse” movement on a slinky cause it to do?
causes the coil to move apart so rarefaction wave passes along the slinky
What are transverse waves?
waves in which the direction of vibration perpendicular to the direction in which wave travels
Examples of transverse waves? (3)
EM waves
secondary seismic waves
waves on a string or wire
What happens when one end of a rope is moved from side to side repeatedly?
sideways movements travel along rope, as each unaffected part of rope pulled sideways when part next to it moves sideways
When are transverse waves plane-polarised?
vibrations stay in one plane only
If vibrations change from one plane to another, what are the transverse wave described as?
unpolarised
What waves cannot be polarised?
longitudinal waves
Example of sources of unpolarised waves (2)
light from filament lamp or a candle
What happens if unpolarised light is passed through a polaroid filter?
transmitted light polarised as filter only allows through light which vibrates in certain direction, according to alignment of its molecules
What happens if unpolarised light is passed through two polarised filters?
transmitted light intensity changes if one polaroid turned relative to other one
What is the filters said to be when the transmitted intensity is a minimum? (polarisation)
crossed
When the filters are polarised can the polarised light from the first filter pass through the second filter?
no
Why can the polarised light not be able to pass through the second filter when the filters are crossed?
alignment of molecules in second filter is at 90° to alignment in first filter
What is light apart of?
spectrum of EM waves
What is the plane of polarisation of an EM wave defined as?
plane in which electric field oscillates
What do polaroid sunglasses do?
reduce glare of light reflected by water/ glass
How do polarised sunglasses work?
reflected light polarised + intensity reduced when it passes through polaroid sunglasses
