Waves and boundaries Flashcards
boundary or interface
where two materials meet
What happens when a sound, water, or light wave reaches the boundary between two materials?
it can be:
- reflected
- refracted
- transmitted
- absorbed
wavelength and the effect on substances and radiation
Different substance do different things which vary with wavelength.
different wavelengths of radiation are absorbed by molecules in the atmosphere by different amounts
reflection and sound waves
sound is reflected when there is a big difference between the densities of the materials at an interface
the greater the difference in density, the more sound energy will be reflected
transmitting and sound waves
sound is transmitted through a material when the densities between the materials are similar
transmitted
a wave is passed through or across a material
refraction
process by which a wave changes speed and sometimes direction upon entering a denser or less dense material
sound, water and light waves can all be refracted
absorbed
energy is taken in by the material and the internal energy of the material will increase
reflection
the wave bounces back off the material
absorption and sound waves
sound can be absorbed by materials
the amount depends on the material and the wavelength of the sound
refraction special case
when a wave moves from one material into another the direction doesn’t change if it moves along the normal
(a wavefront doesn’t travel along the lines but perpendicular to them)
sound waves and refraction
sound waves travel slower in cooler, denser air than warmer, less dense air
this results in a change in direction towards the normal when entering denser air
the waves also slow down, the lines on a diagram get further apart
What determine where the normal is on a boundary?
perpendicular to the boundary
water waves and refraction
water waves travel faster in deep water than in shallow water
this results in a change in direction towards the normal when entering shallower water
the speed also slows down, so the wavefronts get closer together
light waves and refraction
light waves can slow down and change direction when they pass from air to glass
when passing from air to glass they get closer towards the normal
the wavefronts get closer together
On a ray diagram
a) what are the non-refracted and refracted rays called?
b) which angles are measured?
a) incident ray and refracted ray
b) the angles between the incident/refracted rays and the normal
A person blows a dog whistle. The dog is 200m away.
Explain why the dog will hear the whistle faster ona warm day than on a cool day.
air temperature affects the speed of sound
air molecules at a higher temperature have more kinetic energy than air molecules at a lower temperature, so they vibrate faster
since the air molecules vibrate faster, sound waves travel through warm air faster than cooler air
State four things that can happen to a wave at the boundary between two materials
they can be:
- reflected
- refracted
- transmitted or
- absorbed
Explain the changes that occur to a wave during refraction
speed will change
direction may change unless travelling along the normal
wavelength of the wave will change
Suggest how the absorption of infared radiation in the atmosphere is
a) useful
b) a problem
a) stops infared radiation reaching us
could cause overheating/death
b) it stops infared radiation getting to us from space that could help us detect other objects in space
may be useful when it is too cold to keep people or crops warm
may have an impact on studies of the atmosphere or space
How does speed affect wavelength?
they are directly proportional
a lower speed means a smaller wavelength
this means that if a wave slows down at a boundary the wavelength also decreases
(wavelength also has a significant impact on the amount of transmission or absorption)
