waves 3 Flashcards
what’s a transverse wave?
give some examples
perpendicular to direction of travel
no matter is transferred as particles oscillate up and down
water waves, electromagnetic waves, uv, x-ray
what’s a longitudinal wave?
give some examples
parallel to direction of travel
no matter transferred as particles oscillate forwards and back
sound, shock wave, seismic p wave
what’s amplitude?
maximum displacement of oscillation from equilibrium point
measured in meters
relates to how loud sound is
what’s wavelength?
the distance between two consecutive crests on a transverse wave or the distance between two consecutive compressions
measured in meters
what’s time period?
the time for one wave to pass
measured in seconds
what’s frequency?
the number of waves that pass per unit time
measured in Hz
whats the equation for frequency?
frequency = number of waves / time for waves to pass
whats the equation for wave speed?
wave speed = wavelength x frequency
what’s the equation for time period?
time period = 1 / frequency
what’s the electromagnet spectrum?
long wavelength > short wavelength
radio
microwave
infrared
visible
ultraviolet
x-ray
gamma ray
whats the use of radio waves?
broadcasting and communications
whats the use and dangers of microwaves?
cooking food and satellite transmissions
internal heating of body tissue
whats the uses and dangers of infrared?
heater and night vision
skin burns
whats the uses of visible?
human vision, photography and optical fibres
whats the uses and dangers of ultraviolet?
fluorescent lamps
damage to surface cells and blindness
whats the uses of x-ray?
medical equipment
whats the uses and dangers of gamma rays?
sterilising foods, medical equipment
cancer, mutations of cells - to reduce risk exposure for short amount of time
whats reflection?
when light bounces of an even surface
what’s the law of reflection?
angle of incidence = angle of reflection
whats a diffuse reflection?
when light reflects from an uneven surface, the light reflects off at different angles giving a diffuse reflection
whats a clear reflection?
light reflects from an even surface
whats a normal?
a normal is an imaginary line that’s perpendicular to the surface at the point of incidence
shown normally with a dotted line
whats the point of incidence?
where the ray of incidence meets the object
whats the angle of incidence?
the angle between the incidence ray and normal
whats the angle of reflection?
the angle between the reflected wave and the normal
what is refraction?
when waves travel at different speeds in substances which have different densities
when is an angle refracted?
when an angle meets a different medium at an angle therefore the wave changes direction and becomes refracted
how to draw a diagram for a refracted wave:
- draw the 90-degree normal
- draw an incidence ray that meets the normal at the boundary
- angle between ray and normal is the angle of incidence
- now draw the refracted ray (if material is denser that the first the ray will bend towards normal therefore the angle will be smaller that angle of incidence)
practical of internal refraction/critical angle and semicircle glass block:
- shine light ray into glass semi circle block (if semi circle shine light into curve side)
- aim light into curved side at an angle to normal, ray of refraction should bend away from normal
- repeat this, increasing angle of incident by 10 degrees each time, until you react 80 degreed
- trace the incidence and emergent rays onto the piece of paper and remove block then draw refracted ray by joining the two lines together
- try find angle where the refraction in internal refracted, this is the critical angle
practical of prisms dispersing white light:
as you shine white light into a prism you get different wavelengths of light refract by different amounts so white light disperses into its different colours, giving a rainbow effect
whats snells law?
refractive index = sin (incidence angle) / sin (reflective angle)
n = sin i / sin r
to find i = sin -1 ( n sin(r) )
to find r = sin-1 (sin(i) / n )
practical refractive index of glass using a glass block:
- draw around a rectangular glass block on a piece of paper and direct a ray of light through it at an angle
- trace the incidence ray and emergent ray
- remove the block then draw the refracted ray between them
- draw the normal at 90 degrees to edge of block at the point of incidence
- use a protractor to measure the angle of incidence and angle of refraction
- then calculate refractive index using snells law
practical semicircular blocks to show total internal reflection:
- repeat steps from finding refractive index but keep increasing the angle of incidence and the angle of refraction will get closer to 90 degrees and shine light ray at curved bit of block
- when the angle of incidence reaches the critical angle the light is refracted right along the boundary
- any angle greater than the critical angle gives you total internal reflection
- record results in a table
- find critical angle using sin c = 1 / n
how can you use snells law to find the critical angle?
critical angle = 1 / refractive index
n = 1 / sin(c)
c = sin -1 (1 / n)
whats two uses of total internal reflection?
optical fibres - made of plastic or glass and consists of a central core surrounded by cladding with a low refractive index, very narrow so light always hits the core-cladding totally internally reflecting the light to send signals. doesn’t work if fibre is bent too sharply
prisms - allows us to use prisms to see objects that are not in our eye line ( this is how a periscope works) ray of light travels into one prism and is TIR and then into another prism and TIR so the ray is travelling parallel to its initial path but at a different height
are sound waves transverse or longitudinal?
longitudinal
sound waves can be…
reflected and refracted
what is the frequency range for human hearing?
20-20000Hz
how can you measure the speed of sound?
practical
signal generator finds the specific frequency
two microphones and an oscilloscope find the sound waves generated
- the detected waves can be as separate waves on the oscilloscope
- start both microphones next to speaker then slowly move one away until the two waves align and one wavelength apart
- measure the distance between microphones to find wavelength
- using the equation wave speed = frequency x wavelength (frequency is what you set on the signal generator)
roughly what is the speed of sound in air?
340 m/s
finding the frequency of a wave using an oscilloscope:
practical
(x-axis is time)
- adjust the scale to get a clear trace
- adjust time division setting until it shows one complete cycle
- read of the period (time taken for one cycle)
- frequency = 1 / time period
the louder the sound…
oscilloscope
the greater the amplitude
the higher the pitch…
oscilloscope
the higher the frequency of vibrations
what’s a wave front?
front of a wave, drawn to represent the vibrating part of wave
what do all the waves in the electromagnetic spectrum have in common?
transverse waves
travel at the same speed through a vacuum
how do all the waves in the electromagnetic spectrum differ?
wavelength
frequency
what’s the order of colours of the visible light spectrum in terms of increasing wavelength?
violet, indigo, blue, green, yellow, orange, red
how can reflection allow humans to see objects?
when light hits objects it reflects into our eyes
we absorb the colours that are reflected
what’s dispersion?
separation of white light into colours
according to wave length
how is light dispersed through a prism?
the shorter the wavelength of light the more it is refracted
red refracts the least
blue refracts the most
this causes light to spread out to form a spectrum of dispersion
what two conditions are needed for total internal reflection to occur?
angle of incidence must be greater than critical angle
light must travel from a more dense medium to a less dense medium
why can’t sound waves travel through a vacuum?
there is no particles to pass vibrations
what’s an ultrasound and what’s one use?
uses high frequency sound waves to create an image
foetal scanning
what’s the doppler effect?
change in frequency or wavelength of a wave for an observer moving relative to its source
meaning that something is emitting waves and moving so waves punch up at front of objects and spread out the object, but only while its moving
all waves can be …
reflected and refracted
is light a transverse or longitudinal wave?
transverse wave oscillation perpendicular to direction of travel
cane be reflected and refracted
how do you measure the speed of sound in air?
- use a tape measure of position two microphones a distance 2 m apart
- bang a pair of wooden blocks so that sound wave travel past microphone 1 then microphone 2
- when microphone 1 hears the sound the timer starts
- when microphone 2 hears the sound the timer ends
- repeat experiment 5 times to find the average time in seconds take it takes for sound to travel 2. m
- use equation speed = distance / time
