Flashcards in physics paper 2 waves Deck (84):
the distance from one peak to the next
number of complete waves there are per second passing a certain point- 1Hz is 1 wave per second
the maximum displacement of a wave from rest to crest
the period (T)?
the time it takes for 1 complete wave to pass a point
wave speed (m/s)=
frequency (Hz) x Wavelength (m)
the vibrations are perpendicular to direction of energy transferred
the vibrations are parallel as the direction of energy transferred
transverse wave examples
slinky spring moved up and down
waves on strings
ripples on water
longitudinal wave examples
sound and ultrasound
slinky spring pushed at end
what does energy transfer?
information without transferring matter
what does refraction mean?
the waves go through the new material but change direction
what are the 7 types of EM waves
what are EM waves in order of?
increasing frequencies and decreasing wavelength
uses of radiowaves
1)long-wave radio as long wavelengths diffract around the earth
2) TV and FM radio broadcasting-short wavelengths- reception only in direct sight of transmitter as don't diffract
3) short-wave radio signals are reflected off ionosphere-an electrically charged layer in Earth's upper atmosphere so can be received at long distances from the transmitter
uses of microwaves
1)satellite communication- which need to pass through watery atmosphere without being absorbed
2) for satellite TV signal from transmitter is transmitted into space -picked up bu satellite receiver dish orbiting and transmits signal back to Earth in diff directions
4) remote sensing satellites to monitor oil spills, movement of icebergs
5) microwave ovens-cooking-diff wavelength to communications
absorbed by water molecules in food penetrate few before being absorbed. the energy is conducted or convected to other parts of the food
uses of infrared
1-heating-electrical heaters radiate IR for warmth
2-night-vision- turns into electrical signals which are displayed on a screen
uses of UV
1-fluorescent lamps-absorbed and visible light is emitted
2-killing bacteria in water purification
3-killing bacteria in sterilisation of equipment
uses of x-rays
see inside things- medical scans- radiation is directed through object or body onto detector plate-brighter bits are where x-rays can't get through:bone
uses of gamma
1-sterilising medical equipment-kills microbes
2- sterilising food-kills microbes keeps food fresh for longer without freezing
uses of visible light
1)optical fibres- bouncing waves off sides of a very narrow core-enters at a certain angle and reflected until emerges at the other end
-used for telephone and broadband internet cables
- medical purposes to see inside body
2) photography- cameras use a lens to focus visible light onto a light-sensitive film from a sensor
the lens aperture controls how much light enters the camera
the shutter speed is how long the film or sensor is exposed to light
dangers of microwaves and way to protect from it
heat human body tissue- have similar frequency to the vibrations of molecules so increase these=internal heating
- microwave ovens need to have shielding to prevent waves reaching user
dangers of infrared and way to protect from it
skin burns- make surface molecules of substances vibrate=heating effect
- use insulating materials to reduce amount of IR reaching your skin
dangers of ultraviolet and way to protect from it
damage surface cells
causes blindness- it is ionising so carries enough energy to know electrons off atoms= cell mutation or cancer
- wear sunscreen with UV filters
-stay out of strong sunlight
dangers of gamma and way to protect from it
cell mutation leading to tissue damage or cancer- very high frequency waves ionising and penetrate far into body
-radioactive sources of gamma should be kept in lead-lined boxes
-exposure time should be as short as possible
reflection of visible light means?
allows us to see all objects-light bounces off them into our eyes
what's a diffuse reflection?
when light reflects off an uneven surface such as paper and the light reflecs at all different angles
angle of incidence=
angle of reflection defined between i and dotted normal
what's a virtual image?
when the light rays bouncing off an object onto a mirror are diverging so the light from the object appears to be coming from a different place
how do EM waves move in dense media?
how can you experiment with refraction using a light source and a rectangular block?
1-put block on paper
2- shine a light ray at an angle into the block-some light is reflected but most passes through the glass and is refracted
3- trace the incident and emergent rays onto the paper and remove the block. draw in the refracted ray by joining the ends of the two rays
4-should see that as the light passes from air into block, it bends towards the normal because it slows down
5- when light reaches the boundary on the other side of the block, it's passing into a less dense medium so speeds up and bends away from the normal
6- the emergent ray is travelling in the same direction as the incident ray-refracted to the normal and back by the same amount
7- measure the angle of incidence and angle of refraction made with the normal using protractor-calculate using snell's law to find refractive index of material
what do triangular prisms do to white light? and why?
desperse it because diff wavelengths refract by diff amounts so white light disperses into diff colours as it enters the prism because the boundaries aren't parallel, so diff wavelengths don't recombine- rainbow effect- violet is most bent as shortest wavelength
speed of light in vacuum /speed of light in material= n=c/v
what does refractive index tell you?
how fast light travels in that material
why is the refractive index of glass high?
light slows down
what's the refractive index of air?
what's snell's law?
what happens if you keep increasing the angle of incidence?
the angle of refraction gets closer to 90 degrees. eventually i reaches a critical angle C for which r=90. the light is refracted along the boundary
what do you get above the critical angle?
total inernal reflection
when i is less than Critical angle=
most light passes out but a little internally reflected
when i is equal to Critical angle=
emerging ray goes along surface- quite a lot of internal reflection
when i is greater than Critical angle=
no light comes out and all is internally reflected
the higher the refractive index the lower the ?
how do optical fibres use total internal reflection?
made of plastic or glass and consist of a central core surrounded by cladding that has a lower refractive index. the core of the fibre is so narrow that light signals passing through it always hit the core-cladding boundary at angles higher than C- so light is always totally internally reflected. only stops working if fibre is bent tom sharply
what are sound waves and what are they caused by?
they are longitudinal waves and caused by vibrating objects. the vibrations are passed through the surrounding medium as a series of compressions before it reaches your ear drum
what happens to sound waves in denser medium?
they travel faster as they are caused by vibrating particles-so can't travel through a vacuum are there are no particles
what are sound waves reflected by?
how can you use an oscilloscope to measure the speed of sound?
1) attach a signal generator to a speaker at a specific frequency e.g. 1kHz.
2)start with both microphones next to speaker, then slowly move one away until the two waves are aligned on the display, but exactly one wavelength apart
3) measure the distance between the microphones to find the wavelength
4) use formula wave speed= frequency x wavelength to find the speed of sound waves passing through the air- f is whatever the signal generator is set to
5)should be around 340m/s
How are waves diffracted?
They bend round edges and through gaps causing waves to spread out. This allows waves to travel round corners
Wha makes the waves spread out more
The narrower the gap or the longer the wavelength
What happens to the wave if the gap is much wider than the wavelength?
There's little diffraction
What happens to wave if gap is a bury wider than wavelength?
Diffraction only happens at edges
What happens to the wave if the gap is the same as wavelength?
Maximum diffraction and perfect semi- circles
The longer the wavelength of the wave, how much do they diffract?
The more they diffract
how can you communicate any kind of information over long distance?
it needs to be converted into electrical signals
what are the two signals?
analogue and digital
how are these signals sent?
down telephone wires or carried on EM waves
how do analogue signals work?
- it can take any value within a certain range.
-the amplitude and frequency of an analogue wave vary continuously
how do digital signals work?
- can only take two values.
- called on/off or 1/0.
what's an example of digital signals being sent?
send data along optical fibres as short pulses of light
what happens to both analogue and digital waves as they travel?
1- they weaken as they travel so need to be amplified along their route
2- they pick up interference or noise from electrical disturbances or other signals
what happens when an analogue signal is amplified?
the noise is amplified too- so every time the signal loses quality
what happens when a digital signal is amplified?
the noise is ignored so the signal remains high quality
what happens when two or more waves of a similar frequency meet?
they can create one combined signal with a new amplitude- called interference
-happens when two radio stations transmit in similar frequencies
what is easier because digital signals ignore noise?
it's easier to transmit multiple signals using multiplexing
what is multiplexing?
transmit multiple signals at the same time with just one cable or EM wave
why can you use multiplexing with digital signals?
because the signals are easier to tell apart, so can transmit more info along the same chanel
what is quantisation?
the process of 'rounding' multiple values to a smaller set. By doing this, you can pack more information into the same amount of space.
how does quantisation work with digital signals?
as digital can only have two values, quantisation doesn't lose much information
how does quantisation work with analogue signals?
a lot of information is lost when a continuous range is rounded off
how do vinyl records work?
- they are analogue- the needle on a record player goes up and down and side to side over the grooves in the disc forming an analogue wave which is converted to sound
- the grooves eventually wear away and the sound deteriorates- doesn't happen with digital music
what can happen to sound waves?
they can be diffracted through gaps and around obstacles- hear someone talking from around a corner as the sound waves will bend and spread out
what's an oscilloscope?
it displays sound waves
how does an oscilloscope work?
1- a sound wave receiver, such as a microphone, can pick up sound waves travelling through the air
2- to display these waves, and measure their properties, you can plug the microphone into an oscilloscope. The microphone converts the sound waves to electrical signals
3- the oscilloscope is a device which can display the microphone signal as a trace on a screen
4- the appearance of the wave tells you whether the sound is loud or quiet and high or low-pitched
5- you can take detailed measurements to calculate the frequency of the sound by adjusting the settings on the display
what increases with amplitude?
what happens with a greater amplitude?
-the greater the amplitude of a wave or vibration, the more energy is carries- in sound it will be louder
- louder sound waves will have a trace with a larger amplitude on an oscilloscope
the higher the frequency, the higher the?
what is frequency?
the number of complete vibrations each second
what are the units for frequency?
Hz- 1 vibration per second
kHz - 1000 Hz
MHz- 1 000 000 Hz
the more complete cycles displayed on the oscilloscope screen then?
the higher the frequency
if the source of sound vibrates with a high frequency then?
the sound is high-pitched
if the source of sound vibrates with a low frequency then?
the sound is low-pitched