Section 3 - Waves And The Electromagnetic Spectrum Flashcards
What do waves transfer?
Energy
Information
What do particles in a wave do?
Vibrate
What is the amplitude of a wave?
The displacement from the rest position to the trough or the crest
What’s the wavelength of a wave ?
The wavelength of a wave is length of a full cycle of the wave
Distance between 2 identical points
What’s the frequency of a wave ?
What’s frequency measured in?
The frequency of a wave is Number of complete cycles of the wave passing a certain point per second.
Frequency is measured in hertz(hz)
1hz is one wave per second
What’s the period of a wave?
How do we calculate the period of a wave?
The period of a wave is the number of seconds it takes for a full cycle of a wave to pass a certain point
Period= 1/frequency
What type of vibrations do transverse waves have?
Real life example of one
The vibrations are perpendicular to the direction a wave travels
A spring wiggled up and down gives a transverse wave.
Examples of transverse waves …
- all electromagnetic waves
- S-waves ( a type of seismic wave)
-ripples and waves in Water
The vibrations in a longitude wave …
What do they do as they travel through a medium?
What does this cause?
In longitudal waves, the vibrations are parallel to the direction of travel of the wave
They squash up and stretch out the arrangement of particles in the medium as they pass through.
This makes compressions (high pressure) and rarefractions ( low pressure)
Examples of longitudal waves…
Sound waves
P-waves
What is wave speed?
Wave speed is how quickly a wave moves through a place
2 ways to calculate wave speed?
Wave speed = distance/time
Wave speed=frequency(Hz) X wavelength (m)
Equipment to measure the speed of sound?
oscilloscope
Signal generator
Two microphones
Speaker
How do we measure the speed of sound?
-Set up the oscilloscope so the detected waves at each microphone are shown as separate waves
-start with both microphones next to speaker then move one away until two waves are aligned on the display but have moved one wavelength apart
-measure distance between the microphones to find one wavelength
-use the formula v= frequency X wavelength to find the speed of sound waves passing through the air
How to measure the speed of water ripples using a strobe light ?
1)Using a signal generator attached to the dipper of a ripple tank create water waves at a set frequency.
2)dim lights and turn on a strobe light. You’ll see a pattern of waves below
3) alter the frequency of the strobe light until the wave pattern on the screen appears to freeze and stop moving. This happens when the frequency of the waves and the strobe light are equal
4) the distance between each shadow line is equal to one wavelength. Measure distance between lines that are 10 wavelength apparent then find avaradhe wavelength
5) use v=frequency X wavelength to find the speed of the waves.
How do we find speed of waves in a solid ?
Measuring the frequency of sound waves produced when you hit the object
Hitting the rod causes waves to be produced along the rod
These make the rod vibrate and produce sound waves in the air around the rod
These sound waves have the same frequencies as the waves on the rod
Method of finding wave speed in a solid…
1) measure and record the length of a metal rod
2) set up apparatus. Rod attached to clamps by elastic bands, microphone attached to computer on the left of the rod. Hammer on the right of the rod
3) tap the rod with the hammer. Write down the peak frequency displayed by the computer
4) repeat this three times to get an avaradhe peak frequency
5)calculate speed of the wave by using v=frequency X wavelength. The frequency is represented as the rod length X 2
What can waves do at boundaries ?
Be absorbed
Reflected
Transmitted
Refracted
What happens when a wave is absorbed at a boundary?
The wave transfers energy to the materials energy stores
What happens when a wave is transmitted at a boundary ?
The wave carries on travelling through the new material. This often leads to refraction. Refraction can be used in communications
What does what happens to a wave as it reaches an interface depend on?
Wavelength
Properties of the material involved
What can happen at a boundary causing a wave to refract?
The wave changes speed
What happens if the wave hits the boundary at an angle?
The change in speed will cause a change in direction- refraction
What happens in the wave is travelling along the normal ?
The wave will change in speed but not be refracyed
The greater the change in speed …
The more a wave bends
What happens if a wave bends towards the normal?
Away from the normal?
It slows down if it’s travelling towards the normal
It speeds up if it’s travelling away from the normal
How do em waves normally travel in denser materials
Slowly
What effects how much an em wave refracts?
It’s wavelength. Shorter wavelengths bend more
What happens if the wavelength decreases when light travels through a boundary ?
The wave slows down
If it increases, it speeds up
What’s the angle of incidence?
The angle of incidence Is the angle between the ray and the normal
What happens if the second material is denser than the first?
What happens if it’s less dense than the first?
The refracted ray bends towards the normal
The refracted ray will bend away from the normal(angle or refraction is larger than the angle of incidence)
Environment needed for the refraction practical?
Dim room so you can clearly see the ray
Ray of light must be thin
Use a ray box that has a lightbulb in it
How to carry out the core practical that investigates light refracting at the boundary between air and glass ?
1) place a rectangular block on a piece of paper and trace around it. Use a ray box to shine light at one side of the block
2) trace the incident ray and emergent ray on the other side of the block. Remove the block and with a straight line join up the incident ray and emergent ray to show the path of the refracted ray
3) draw the normal at the point where the light ray entered block. Use a protractor to measure the angle of incidence and the angle of refraction. do the same for the point where the ray emerges from the block
4)repeat three times keeping the angle of incidence where the ray enters the block the same. Calculate the averages for each of the angles
What you should find from the refraction practical
-Light bends towards the normal as it enters the block. This is because the air has a lower density than glass, so the light ray will always slow down when it enters the block.
- you should then see the light ray bends away from the normal as it leaves the block, this is because light rays speed up as it leaves the block and travels through air
What’s the law of reflection?
angle of incidence = angle of reflection
What does total internal reflection depend on?
The critical angle
What does total internal reflection mean?
reflected back into the material
Where can total internal reflection occur?
When a wave travels through a dense material into a less dense substance
Angle of incidence larger than the critical angle
What’s needed for total internal reflection to occur?
The angle of incidence must be larger than the critical angle . Every boundary has its own different critical angle
What’s specular reflection ?
When waves are reflected in a single direction by a smooth surface
What’s the result of specular reflection?
Example.
You get a clear reflection.
Eg: light reflected by a mirror
What is diffuse reflection?
Diffuse reflection occurs when waves are reflected by a rough surface And waves are reflected in all directions
Why does diffuse reflection occur?
Diffuse reflection occurs because the normal is different for each incident ray
What does the surface of diffuse reflection look like?
The surface looks matte, you don’t get a clear reflection
What are sound waves caused by?
Vibrating objects
What type of wave are sound waves ?
What happens when they travel through a medium?
What happens when they travel through a solid?
Sound waves are Longitudal waves
The vibrations are passed through a medium as a series of compressions and rarefractions
When sound waves travel through a solid they do so by causing particles to vibrate
What determines the frequencies of sound an object can transmit?
Size
Shape
Structure
Of the object
What do sound waves travel the fastest - slowest in
Fastest = solids
Liquids
Slowest = Gasses
How does the Wavelength change as the wave speed does?
It gets longer when the wave speeds up. Shorter when it slows down
What causes echoes/sound waves being reflected
Hard/flat surfaces
Why can’t sound waves travel in space?
Because it’s mostly a vacuum.
There are no particles to move or vibrate
How do we hear sound ?
1)Sound waves reach the ear drum and vibrate
2)these vibrations are passed on to tiny bones called ossicles, through semicircular canals to the cochlea.
3) the cochlea turns these vibrations into electrical signals which get sent to the brain.
4) the brain interprets these signals as sound of different volumes, depending on their frequency and intensity. A higher frequency sound wave has a higher pitch.
What’s human hearing limited by ?
Size and shape of our eardrum. The structure of all the parts within the ear that vibrate to transmit the sound wave
What is infrasound?
Frequencies with lower than 20hz
Animals that communicate using infrasound..
Elephants and wales. Scientists are able to track these animals for conservation purposes
How can scientists predict that a volcano is about to erupt?
By using infrasound. Volcanoes avalanches and earthquakes produce infrasound
What is ultrasound?
Frequencies with higher than 20000 hz