3 Waves Flashcards
what is hertz measuring
the frequency of something
what is the frequency of a wave
the amount of cycles per second
the pitch
longitudinal waves
the waves oscillate in the parallel (same direction) to the direction they travel in
transverse waves
the waves oscillate perpendicular (at right angles) to the direction they travel in
examples of longitudinal waves
sound waves
seismic p-waves
spring/slinkie
examples of transverse waves
electromagnetic waves
ripples in the sea
mexican wave
seismic s-waves
rope
what is the amplitude of a wave
The distance from the undisturbed position to the peak or trough of a wave
the volume
what is the wavefront of a wave
the wavefront is a way of drawing a wave from above (all of the waves are drawn in the same phase, eg all troughs)
each line represents one wave and if they are close together that shows a high frequency
what is the wavelength of a wave
The distance from one point on the wave to the same point on the next wave
what is the period of a wave
the time it takes for one wavelength to happen
what do waves transfer
transfer energy and information, without transferring matter
what is the formula with wavelength, frequency, wave speed
wave speed = frequency x wavelength
v=fλ
what is the formula with frequency and time period
frequency = 1 / time period
f=1/T
what is the doppler effect
the change in wavelength and frequency of a wave emitted by a moveing source
why does the doppler effect change the frequency of a wave
When the source of the wave is moving towards the observer, each successive wave cycle is emitted from a position closer to the observer than the previous cycle. As a result, the time between the arrival of each wave at the observer is reduced, which effectively increases the frequency of the wave as observed by the observer2.
Conversely, if the source of the wave is moving away from the observer, each wave cycle is emitted from a position farther from the observer than the previous cycle. This increases the time between the arrival of each wave at the observer, effectively reducing the observed frequency
why does the doppler effect change the wavelength of a wave
When the source of the wave is moving towards the observer, each successive wave cycle is emitted from a position closer to the observer than the previous cycle1. This causes the wavefronts to “bunch up”, effectively shortening the wavelength as observed by the observer3. This is why waves appear “squeezed” or “compressed” when the source is moving towards the observer4.
Conversely, if the source of the wave is moving away from the observer, each wave cycle is emitted from a position farther from the observer than the previous cycle1. This causes the wavefronts to spread out, effectively lengthening the wavelength as observed by the observer3. This is why waves appear “stretched out” when the source is moving away from the observer
can all waves be reflected or refracted
yes in the right circumstances
what type of wave is light waves
transverse
can light waves be reflected or refracted
yes
what is the law of reflection
The law of reflection states that the angle of incidence (the angle at which the wave hits the surface) equals the angle of reflection (the angle at which the wave bounces off the surface).
what is reflection
A wave hits a boundary between two media and does not pass through, but instead stays in the original medium
where angle i = r
what is the formula with refractive index, angle of incidence, angle of refraction
refractive index = sin(angle of incidence) / sin(angle of refraction)
n = sin(i) / sin(r)
practical: To investigate the refraction of light using rectangular blocks, semi-circular blocks and triangular prisms
Place the block on a sheet of paper, and carefully draw around the rectangular perspex block using a pencil
Switch on the ray box and direct a beam of light at the side face of the block
Mark on the paper:
- A point on the ray close to the ray box
- The point where the ray enters the block
- The point where the ray exits the block
- A point on the exit light ray which is a distance of about 5 cm away from the block
Draw a dashed line normal (at right angles) to the outline of the block where the points are
Remove the block and join the points marked with three straight lines
Replace the block within its outline and repeat the above process for a ray striking the block at a different angle
Repeat the procedure for each shape of perspex block (prism and semi-circular)
practical: investigate the refractive index of glass using a glass block
Place the glass block on a sheet of paper, and carefully draw around the rectangular perspex block using a pencil
Switch on the ray box and direct a beam of light at the side face of the block
Mark on the paper:
- A point on the ray close to the ray box
- The point where the ray enters the block
- The point where the ray exits the block
- A point on the exit light ray which is a distance of about 5 cm away from the block
Draw a dashed line normal (at right angles) to the outline of the block where the points are
Remove the block and join the points marked with three straight lines
Replace the block within its outline and repeat the above process for a ray striking the block at a different angle
measure the angle of incidence and angle of refraction and then use n = sin(i) / sin(r)
what is total internal reflection
Total Internal Reflection (TIR) is where waves arriving at the boundary from one medium to another (e.g., from water to air) are not refracted into the second (“external”) medium, but completely reflected back into the first (“internal”) medium
when does total internal reflection happen
The angle of incidence is greater than the critical angle and the incident material is denser than the second material
what are the conditions needed for total internal reflection
The angle of incidence > the critical angle
higher refractive index than air
when a ray tries to go from a denser to a less dense material
how is total internal reflection used in optical fibres
they are made of glass or plastic with in outer cladding which has a lower refractive index than the glass
which means that the light will always hit a boundary at a higher value than the critical angle
the light waves are totally internal reflected down whole wire meaning all of the wave reaches the other end which allows all of the information to to be passed through the fibre without any being lost
what is the critical angle
the angle where the light is refracted along the boundary of the surface
As the angle of incidence is increased, the angle of refraction also increases until it gets closer to 90°
When the angle of refraction is exactly 90° the light is refracted along the boundary
At this point, the angle of incidence is known as the critical angle c
what is the formula with critical angle and refractive index
sin(critical angle) = 1 / refractive index
sin(c)=1/n
what type of wave is a sound wave
longitudinal waves
can sound waves be reflected and refracted
yes
what is the frequency range of human hearing
20Hz - 20,000Hz
practical: investigate the speed of sound in air
have 2 people stand 300 meters (measured with a trundle wheel) away from each other
one has a pair of cymbals and the other has a stopwatch
the person with the cymbals hits them together and then the stopwatch person starts the timer when they see the cymbals hit and stops it when they hear the sound.
record the time
repeat this 3 times and work out average time
s=d/t
increase distance and repeat
how can a oscilloscope and microphone be used to display a sound wave
Microphone Connection: A microphone is connected to an oscilloscope. The microphone captures sound waves and converts them into electrical signals
Signal Conversion: The oscilloscope takes these electrical signals and converts them into a visual representation, displaying them as transverse waves on its screen
practical: investigate the frequency of a sound wave using an oscilloscope
Connect the microphone to the oscilloscope
Test the microphone displays a signal by humming
Adjust the time base of the oscilloscope until the signal fits on the screen - ensure that multiple complete waves can be seen
Strike the tuning fork on the edge of a hard surface to generate sound waves of a pure frequency
Hold the tuning fork near to the microphone and observe the sound wave on the oscilloscope screen
Freeze the image on the oscilloscope screen, or take a picture of it
Measure the number of squares for one complete cycle
multiply the number of squares by the time base to find the time period
frequency = 1/T
how does the pitch of a sound relate to the frequency of vibration
the higher the pitch of a sound, the higher frequency the wave has
how does the volume of a sound relate to the amplitude of vibration
the higher the amplitude of a wave, the louder the sound is
what happens to a wave if it enters a more dense material at an angle
it will bend towards the normal
what happens to a wave if it enters a less dense material at an angle
it will bend away from the normal
what is light part of
a continuous electromagnetic spectrum that includes radio, microwave, infrared, visible, ultraviolet, x-ray and gamma ray radiations, and that all these waves travel at the same speed in free space
order of the EM spectrum, in terms of decreasing wavelength and increasing frequency
low energy, long wavelength, low frequency
radio
microwaves
infared
visible
ultraviolet
xray
gamma
high energy, short wavelength, high frequency
order of colours of the visible spectrum
longest wavelength, low frequency
red
orange
yellow
green
blue
indigo
violet
short wavelength, high frequency
uses of radiowaves
broadcasting and communications
uses of microwaves
cooking and satellite transmissions
uses of infrared
heating and night vision equipment
uses of visible light
photography + optical fibres
uses of ultraviolet
fluorescent lamps + tanning beds
uses of xrays
observing internal structure of objects and materials including for medical uses
uses of gamma rays
sterilising food and medical equipment
effects of excessive exposure of microwaves
internal heating of body tissue -> prevented with metal walls and metal grid in glass door
effects of excessive exposure of infrared
surface skin cell burns -> prevented with protective clothing
effects of excessive exposure of ultraviolet
damage to surface skin cells and blindness -> prevented with sunglasses for eyes and suncream for skin
effects of excessive exposure of gamma rays
cancer + mutation -> prevented with minimal exposure and lead clothing
effects of excessive exposure of xrays
cancer + mutation -> prevented with minimal exposure and lead clothing
effects of excessive visible light wave exposure
vision impairments -> don’t look into the sun and wear sunglasses
what speed do waves travel at in a vacuum
all travel at speed of light
