waves Flashcards
EM wave spectrum from lowest to highest frequency
radio, microwaves, IR, visible, UV, X-ray, gamma
uses of radio waves
broadcasting and communications
uses of microwaves
cooking and satellite transmissions
uses of infrared waves
heaters and night vision equipment
uses of visible light
optical fibres and photography
uses of ultraviolet waves
fluorescent lamps
uses of x-rays
observing the internal structure of objects and materials and medical applications
uses of gamma rays
sterilising food and medical equipment
dangers of microwaves
internal heating of body tissue
dangers of infrared waves
skin burns
dangers of ultraviolet waves
damage to surface cells and blindness
dangers of gamma rays
cancer, mutations
what are waves
waves are a disturbance in a medium which transfers energy and information
what are transverse waves
waves in which the particles vibrate perpendicular to wave movement
transverse wave examples
light waves, water waves, S-waves, EM waves
what are longitudinal waves
waves in which the particles vibrate parallel to wave movement
longitudinal wave examples
sound waves, P-waves
what is the time period in waves
time taken for one complete wave/cycle
what is frequency in waves
the complete number of waves per second
how do you measure the speed of sound with microphones
- use speed = distance/time
- measure the distance between the two microphones using a tape measure
- distance must be more than 1 metre
- measure the time it takes for sound to travel from microphone A to microphone B
- repeat and take average
how do you measure the speed of sound using ears
- use speed = distance/time
- measure the distance between the two people using a trundle wheel
- distance must be more than 100m
- measure the time taken from when student sees the clap to when they hear it using a stop watch
- repeat and take average
optical fibres:
- outer cladding has lower refractive index than inner core
- light is transmitted down optical fibres by total internal reflection
- optical fibres can bend to carry light to hard to reach places
doctors use endoscopes to look inside the body of a patient. explain how optical fibres are used in endoscopes.
- optical fibres bend
- some fibres carry light to the inside of the patient
- some fibres transmit the reflected light
- light passes up/down fibres by total internal reflection
- light is reflected inside the patient
- image is analysed by computer
how is light reflected in right-angled prisms
light is totally internally reflected
-> the image appears as a refection at 90 degrees to and below the object
what happens when a ray goes from dense to less dense?
it reflects away from the normal
what does it mean when the ray refracts at 90 degrees to the normal
angle of incidence = critical angle
what happens when the angle of incidence > critical angle
the ray undergoes total internal reflection.
what is the critical angle
- the angle of incidence
- above which gives total internal reflection
law of reflection
angle of incidence = angle of reflection
snells law
n = sin(i)/sin(r)
what is refractive index
a measure of how much a material slows down light waves, and therefore, how much they refract
method to determine refractive index:
- shine a ray of light through the material at an angle
- measure the angle of incidence, from the normal, with a protractor
- measure the angle of refraction, from the normal, with a ruler
- plot a graph of sin(i) against sin(r)
- gradient = refractive index
what happens when a light wave goes from something not very dense to something dense
the light wave slows down
what happens if a wave has constant frequency but slows down
the wavelength would decrease
what is refraction
a wave changing direction when it moves from one material to another
-> this happens because the wave speed changes when moving from one material to another
perspex box practical
- place a Perspex box in the middle of a sheet of paper and draw around it
- remove the block
- find the middle of one of the longer sides of the block
- draw a line at 90 degrees to the side of the glass block at this point - this is the normal
- use a protractor to draw a line at 20 degrees to the normal
- replace the block
- use the ray box and a single slit to shine a ray of light along the line you have drawn - this is the incident ray
- look at the ray of light inside the block after leaving it
- mark 2 dots on the path of the emergent ray with a pencil
- remove the block switch off the power supply
- use the ruler to draw the emergent ray
- use the ruler to mark the path of the refracted ray inside the block
- use a protractor to measure the angle between the refracted ray and the normal - this is called angle of refraction
what can sound waves be displayed as
oscilloscopes
how to find frequency using an oscilloscope:
- connect oscilloscope to microphone
- adjust oscilloscope to get steady rate
- adjust time base to a minimum of one complete cycle on screen
- measure the number of squares for one complete cycle
- multiply the number of squares by the time base to find time period
- use frequency = 1/time period
how to oscilloscopes display sound waves
as a trace on a screen
what is the Doppler effect
describes how the frequency of waves changes when the source and observer are moving relative to each other
what happens to the observed wavelength and observed frequency when the source is moving towards observer
wavelength - decreases
frequency - increases
what happens to the effect on sound and effect on light when the source is moving towards observer
effect on sound - higher pitch
effect on light - more blue
what happens to the observed wavelength and observed frequency when the source is moving away from observer
wavelength - increases
frequency - decreases
what happens to the effect on light and effect on sound when the source is moving away from observer
effect on sound - lower pitch
effect on light - more red
what happens to the observed wavelength and observed frequency when there is no relative motion
wavelength - no change
frequency - no change
what happens to the effect on light and effect on sound when there is no relative motion
effect on sound - no change
effect on light - no change
what is ultrasound
frequencies more that 20,000 Hz
what is sound
frequencies between 20 - 20,000 Hz
what is infrasound
frequencies less than 20 Hz
what is the human hearing range
20 - 20,000 Hz
are sound waves transverse or longitudinal
longitudinal
how is an echo formed
sound waves reflecting off surfaces
when playing a drum how is sound produced?
- the drum skin vibrates
- vibrations are passed onto particles in the air
- vibrations are parallel to the direction of wave movement
amplitude definition
the height of the wave (from rest to crest)
wavelength definition
distance from one peak to the next
period of wave definition
time taken for one complete wave to pass a point
wave speed =
frequency x wavelength
frequency =
1 / time period
sin(c) =
1/n
critical angle =
1/refractive index
