p5 Flashcards
Wavelength
Distance between 1 point on a wave and the same point on the next wave
Amplitude
Distance from equilibrium line to maximum displacement (crest or trough)
Frequency
Number of waves that pass a single point per second
Period
Time taken for a whole wave to completely pass a single point
Relationship between frequency and velocity
Directly proportional
Relationship between wavelength and velocity
Directly proportional
Relationship between period and frequency
Inversely proportional
Transverse waves
Have peaks and troughs, vibrations are straight angled to the direction of travel.
Transverse waves examples
Light, EM, water ripples
Longitudinal waves
Compressions and rare fractions, vibrations in same direction as direction of travel
Longitudinal waves example
Sound waves, ultrasound waves
What is a medium
Substance that waves pass through (air, water, glass)
how does frequency change with medium
It doesn’t
What is optical density (density of a medium)
measures the ability of an object to slow or delay the transmission of light
Not necessarily physical density
Passing into a denser medium
The speed of the wave decreases, so wavelength decreases
Speed decreases because
it is travelling through a more dense medium, so it can’t travel fast
Energy of the wave must be constant because of conservation of energy. So this means frequency stays the same, colour is dependant on frequency so colour stays the same
What can happen at an interface, and what does it depend on?
Reflection, transmission or absorption , depends on the electrons in the material
Electrons can only absorb certain amounts of energy which is directly related to frequency (higher f= more energy). So light of diff frequencies interact diff
Reflection
Waves will reflect of a flat surface, the smoother the surface, the stronger the reflected wave is
Rough surfaces scatter the light in all directions, so appear matt and not reflective
Angle of incidence = angle of reflection
Transmission
Waves will pass thru a transparent material. The more transparent, the more light will pass thru the material. It could still refract, but the process of passing thru the material and still emerging is transmission
Absorption
If the frequency of a light matches the difference in energy less of the electrons, the light will be absorbed by the electrons and not re-emitted except over time as heat
If a material appears a certain colour, only that colour light has been reflected, and the rest of the frequencies i visible light have been absorbed
What happens when ultrasound reaches a boundary between 2 media
They are partially reflected back. The remainder of the waves continue and pass through. A receiver next to the emitter can record the reflected waves
In ultrasound what can the time between emission and detection show
The distance from the source at which they were reflected, as the speed of the wave is constant
When will light reflect
If the object is opaque and not absorbed by the material. The electrons will absorb the light energy, then remit it as a reflected wave
What can ultrasound be used for
Imaging under surfaces (foetus scan, finding cracks in metal)
Sonar
Waves undergo the same processes atps ultrasound, but on a larger sale
How does the ear work
1) outer ear collects sounds and channels it down the ear canal- it acts as an air pressure wave
2) the sound waves hit the eardrum causing it to vibrate at the same frequency as the sound as the incoming pressure waves reach it (compressions force the eardrum inward, rarefactions force the eardrum outward)
3) the small bones connected to the eardrum also vibrate at the same frequency. They act as an amplifier of the sound waves and transfer the compression waves to the fluid in the cochlea
4) as the fluid moved small hairs in the cochlea move too, each hair respond to different frequencies, so they move differently
5) each hair is attached to a nerve cell, so a specific frequency is received. This triggered an electrical impulse to the brain, which interpreted this as sound
Limitations of frequency range
20-20000 Hz
As you get older you hear less due to changes in inner ear
You can only hear certain frequencies due to adaptations
What is a ripple tank
Shallow glass tank containing a fluid with a needle or paddle which oscillates, producing water waves at a chosen frequency.
What would happen if you shone light thru a ripple tank
Dark and light patches would appear underneath it as light passes thru wave crests and troughs
Troughs appear light
Crests appear dark - greater depth of water so light is scattered the most
How to calculate frequency in ripple tank
Count number of times dark (max) passes thru point in a minute, then driving by 60
How to measure wavelength in ripple tank
Using a strobe light at same frequency as the waves, so the pattern of waves appears fixed on the screen.
How can reflection be shown in a ripple tank
Using an obstruction
How can refraction be shown in a ripple tank
By placing a thick glass sheet on part of the tank floor. The depth of the water becomes shallower in that area. Since wave speed depends on depth, the ripples show down in the shallow area
Evidence of particles in waves
Particles travel perpendicular to the direction of the waves travel
If a ping pong ball is placed in a ripple tank, it doesn’t get carried by the wave, it just moves up and down, not in the direction of the wave
This proves evidence that it is the wave travelling, not the water itself
What is the velocity of EM in space (vacuum)
3 x 10 ^8 m/s
Why don’t EM waves need particles to move to transfer energy
They are transverse waves
Frequency wavelength relationship for EM waves
Speed is constant for all EM waves, therefore as wavelength decreases, frequency must increase. As frequency increases, the energy of the wave increases
EM spectrum order
RMIVUXG
Radio waves uses
Communications
Microwaves uses
Cooking
Visible waves uses
Short range communication, remote controls
Visible waves uses
To illuminate things so we can see them
UV wave uses
Sterilisation, as it kills bacteria
X-ray wave uses
To see thru soft tissue and look at skeleton
Gamma wave uses
Kill cancer cells in radiotherapy
Which EM waves are dangerous
UV, X-ray and gamma, as they have a small wavelength, high frequency and therefore high energy . The high energy means they can cause cells to mutate- cancer
