waves and the electromagnetic spectrum Flashcards
What do waves transfer?
Energy and information in the direction they travel but they don’t transfer matter
When waves travel through a medium, what do they do?
Particles of the medium vibrate and transfer energy and information between other / overall particles stay in same place
What is the amplitude?
The displacement from the rest position to a crest or trough
What is the wavelength?
Length of a full cycle of the wave
What is the frequency?
Number of complete cycles of the wave passing a certain point per second.
What is frequency measured in?
hertz (Hz)
1 Hz is 1 wave per second
What is the period of a wave?
Number of seconds it takes for one full cycle.
Period = 1/frequency
What type of vibrations do transverse waves have?
If you drop a twig in water, what happens?
Ripples form and move across the water’s surface. Ripples don’t carry the water away with them though
What is wave velocity?
Distance travelled by a wave per unit time
What is wave front?
an imaginary surface that we draw to represent the vibrating part of a wave
What vibrations do transverse ways have?
Sideways
What does a transverse wave look like?
A spring wiggled up and down (vibrations)
What are types of transverse waves?
Electromagnetic waves
S-waves
Ripples and waves in water
What are the vibrations in transverse waves?
Vibrations are perpendicular (90°) to the direction the wave travels
What vibrations do longitudinal waves have?
Paralled
What are examples of longitudinal waves?
Sound waves and P-waves (seismic wave)
What do longitudinal waves look like?
Squash up and stretch out the arrangement of particles in the medium they passed through, making compressions (high pressure, lots of particles) and rarefactions (low pressure, fewer particles)
How to calculate wave speed? (2 ways)
Frequency x wavelength
OR
distance / time
How do we measure the speed of sound? (Equipment)
You can use two microphones and an oscilloscope to find the wavelength of sound waves generated
How do we measure the speed of sound? (In detail)
1) Set up the oscilloscope so the detective waves are each microphone are shown as separate waves
2) start with both microphones next to the speaker, then slowly move on away until the two waves are aligned on the display, but have moved exactly one wavelength apart.
3) measure the distance between the microphone to find one wavelength
4) Use the formula of waves speed = frequency x wavelength to find the speed of the sound waves passing through the air - the frequency is whatever you set the signal generator to in the first place
How do you measure the speed of water ripples using a strobe light?
1) using a signal generator attached to the dipper of a ripple tank, you can create water waves at a set frequency.
2) dim the lights and turn on the strobe light – you’ll see a wave pattern made by the shadows of the wave crust on the screen below the tank.
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 – the waves appear not to move because they are being lit at the same point in the cycle each time.
4) distance between each shadow line is equal to one wavelength. Measured the distance between the lines that are 10 wavelengths apart, then find the average wavelength.
5) use wave speed = frequency x wavelength to calculate the speed of the waves
How do we use peak frequency to find a speed of waves in solids?
Measuring the frequency of the sound waves produced when you hit the object. For example, hitting the rod causes waves to be produced along the rod. These waves make the rod vibrate and produce soundwaves in the air around the rod. These soundwaves had the same frequencies as the waves in the rod.
How do we use peak frequency to find the speed of waves in solids? (In detail)
1) measure and record the length of a metal rod
2) set up the apparatus, making sure to secure the rod at its centre
3) tap the rod with the hammer. Write down the peak frequency displayed by the computer.
4) repeat this three times to get an average peak frequency
5) calculate the speed of the way using the equation wave speed = frequency x wavelength, where the frequency is equal to twice the length of the rod
What equipment do we need to use peak frequency to find the speed of waves in solids?
- rod
- hammer
- Elastic bands
- clamps
- Microphone
Describe an experiment to measure the wavelength of water wave.
- Attach a signal generator to a dipper and place it in ripple tank filled with water to create some waves
- place the screen underneath the ripple tank, then turn on a strobe light and dim the other lights in the room
- Adjust the frequency of the strobe light until the ripples appear to freeze
- Measure the distance between the shadows on the screen beneath the tank – this is equal to the wavelength of the ripples
Different substances may …. waves when crossing a boundary
- absorb
- transmit
- Reflect
- refract
What happens when waves are absorbed?
The wave transfers energy to the materials energy stores. Often, the energy is transferred to a thermal energy store, which leads to heating.
What happens when a wave is transmitted?
The wave carries on travelling through the new material. This often leads to refraction. This can be used in communications as well as in the lenses of glasses and cameras.
What happens when a wave is reflected?
The incoming ray is neither absorbed or transmitted, but is instead sent back away from the second material. This is how echoes are created.
What is optical density?
Refraction of light
Refraction - Waves changing direction at a boundary
1) wave crosses a boundary between materials it changes speed
2) if the wave hits the boundary at angle the change of speed causes a change in direction - refraction
3) if the wave is travelling along the normal it will change speed, but it’s not refracted
4) The greater the changing speed, the more wave bends (changes direction)
5) the wave bends towards the normal if it slows down. It bends away from the normal if it speeds up.
6) how much a wave refracts depends on its wavelength (EM waves with short wavelengths bend more)
What do wavefront diagrams help to show?
Refraction
How do wavefront diagrams help to show refraction?
1) when one part of the wave from crosses a boundary into a dens material, that part travel slower than the rest of the wavefront
2) so by the time the front crosses the boundary, the faster part of the wavefront will have travelled further than the wavefront
3) this difference in distance travelled by the way front causes the wave to bend
What are rays?
Straight lines that are perpendicular to wavefronts
What is a normal?
Imaginary line
What do ray diagrams show?
Show the path that a wave travels
What is the angle of incidence?
Angle between the incoming ray and the normal
What is the angle of refraction?
Angle between the refracted ray and the normal
What are some needs when investigating refraction?
- Room must be dimmed so you can clearly see the ray
- The ray of light must be thin so you can see the middle of the right when tracing it and measuring angles from it
What is a raybox?
An enclosed box that contains a lightbulb
How can we use a glass block to investigate refraction?
1) rectangular glass block on a piece of paper and trace around it. Use a box to shine the ray of light at the middle of one side of the block
2) trace the incident ray and the emergent ray on the other side of the block. Remove the block and, with a straight line, drawing up the incident ray and the emergent ray to show the path of the refracted ray through the block.
3) the normal at the point where the light rate entered the block. Use the protractor to measure the angle between the incident ray and the normal and the angle between the refracted ray and normal.
4) do the same for the point where the ray emerges from the block
5) repeat this three times, keeping the angle of incident as the right enters the block the same
6) calculate an average for each of the angles
What are the results of using a glass block to investigate refraction?
- The ray of light that bends towards the normal as it enters the block, this is because it has one of the lowest optical densities that there is so the light ray will almost always slow down when it enters the block
- The ray of light bends away from the normal as it leaves the block. This is because the light rays speed up as it leaves the block and travels through the air.
What are electromagnetic waves?
Transverse waves
Electromagnetic waves all travel at what speed through a vacuum?
The same speed
How are EM waves generated?
By a variety of changes in atoms and their nuclei, giving a large range of frequencies
What are the order of waves in order of long wavelength and low frequency?
Radio waves
Microwave
Infrared
Visible light
Ultraviolet
X-rays
Gamma rays
What is the wavelength of radio waves?
1m - 10 (4) m
What is the wavelength of microwaves?
10(-2) m
What is the wavelength of infrared?
10(-5) m
What is the wavelength of visible light?
10(-7) m
What is the wavelength of ultraviolet?
10(-8) m
What is the wavelength of x-rays?
10(-10) m
What is the wavelength of gamma rays?
10(-15) m
How do EM waves transfer energy and given an example?
Transfer energy from a source to an absorber
When you warm yourself by an electric heater, infrared waves transfer energy from the thermal energy store (the source) of the heater to your thermal energy store (the absorber)
The higher the frequency of an AM wave what does it transfer?
More energy
How does radio waves cause human health damage?
Radio waves are transmitted through the body without being absorbed
How do microwaves cause human health damage?
Some wavelength of microwaves can be absorbed, causing heating of cells, which may be dangerous
How do infrared and visible light damage human health?
They are mostly reflected or absorbed by the skin, causing some heating of cells. Infrared can cause burns to the skin if it gets too hot.
How do ultraviolet waves cause human health damage?
Can be absorbed by the skin, but it has a high frequency, so it is potentially more dangerous. It’s a type of ionising radiation and when absorbed it can cause damage themselves on the surface of your skin which could lead to skin cancer. It can also damage your eyes and cause of variety of conditions or even blindness.
How are x-rays and gamma rays damaging to human health?
They are both ionising, so they can cause mutations and damage cells which can lead to cancer. They have high frequencies, so transfer even more energy, causing even more damage. They can pass through the skin and be absorbed by deep issues.
Explain why gamma rays are more dangerous to humans than visible light
Gamer ionising so they can cause tissue damage and cancer, but but visible light isn’t ionising. They carry more energy than visible light, so they’re potential for damage is higher.
How are radio waves made?
Oscillating charges
What colours are shown in radio waves?
Grey
What colour are microwaves?
Light red
What colour is infrared?
Red
What colour is the visible light?
Red orange, yellow, green, blue, indigo and violet
What colour is ultraviolet?
Violet
What colour is x-rays?
Light violet
What colour are gamma rays?
Grey
Our eyes can only detect a small part of the electromagnetic spectrum, what are the waves we can see?
Visible light
When waves increase frequency, what can cause damage to?
Humans
What EM waves made up of?
Oscillating electric and magnetic fields
What are alternating currents made up of? (Explain)
Oscillating charges.
As the charges oscillate , they produce oscillating electric and magnetic fields i.e electromagnetic waves.
How do radio waves contribute to the use of electromagnetic radiation?
Including broadcasting, communicating and satellite transmissions
How do microwaves contribute to the use of electromagnetic radiation?
Cooking, communications and satellite transmissions
How does infrared contribute to the use of electromagnetic radiation?
Cooking, thermal imaging, short range communications, optical fires, television remote controls and Security systems
How do you visible light contribute to the use of electromagnetic radiation?
Vision, photography and illumination
How can ultraviolet contribute to the use of electromagnetic radiation?
Security marking, fluorescent lamps, detecting forged banknotes and disinfecting water
How can x-rays contribute to the use of electromagnetic radiation?
Observing the internal structure of objects, airport security scanners, and medical x-rays
How do gamma rays contribute to the use of electromagnetic radiation?
Sterilising food and medical equipment, and the detection of cancer and its treatment
How can we produce radio waves using an alternating current in electrical circuits, using a transmitter?
1) when transmitted radio waves reach a receiver, the radio waves are absorbed
2) The energy carried by the waves is transferred to the electrons in the material of the receiver
3) this causes the electrons to oscillate, if the receiver is part of a complete electrical circuit, it generates an alternating current
8) this has the same frequency as the radio wave that generated it
How do long wave radio waves work?
Long wavelength spend around the curve surface of the Earth - this makes it possible for radio signals to be received, even if the receiver isn’t in the line of sight of the transmitter
Changes in atoms and nuclei can…
Generate radiations over a wide frequency range
Be caused by absorption of a range of radiations
How do short-wave radio signals work?
They can be received from long distances by the transmitter because they are reflected by the Earth’s atmosphere
Example of a short radio wave?
Bluetooth uses short wave radio waves to send data over short distances between devices without wires
Microwaves and radio waves are used by what?
Satellites
How do satellites work? Give an example
Communication to and from satellites used EM waves which can pass easily through the Earth’s watery atmosphere. These waves are usually microwaves, but can sometimes be relatively high frequency radio waves
For satellite TV, the signal from a transmitter is transmitted into space and picked up by the satellite receiver dish orbit between thousands of kilometres above the Earth. Satellite transmits the signal back to different direction, received by satellite dish on the ground.
How do microwave ovens use microwaves?
1) the microwaves are absorbed by water molecules and food
2) the microwave penetrate up to a few centimetres into the food before being absorbed and transferring the energy they are carrying to the water molecules and the food, causing the water to heat up
3) the water molecules done transfer the skin to the rest of the molecules in the food by heating – which quickly cooks the food
What is infrared radiation given out by?
All hot objects
What are uses of infrared radiation?
(Heat)
- increase or monitor temperature
- thermal imaging
- infrared sensors
- electric heaters
What are uses of infrared radiation?
Information
- send files between mobile phones
- optical fibres that carry data
What does visible light use?
Example
Photography
Digital cameras contain image sensors, which detective visible light and generate in the electrical signal. The signal is then converted into an image that can be stored digitally or printed.
What are example of ultraviolet when used in fluorescent lamps?
- security pens used to mark property - and you feel like the incredible glow, but it’s invisible otherwise
- sterilising water - bacteria in the water making it safe to drink
Uses of x-rays
- view internal structure of objects and materials
- radiographer in hospitals use x-rays
- airport security scanners
Uses of gamma rays
- food can be realised killing bacteria – keeps the food fresh for longer
- Cancer treatment
- Medical imaging
Explain why signals between satellites are usually transmitted as microwaves
Can pass easily through Earth’s watery atmosphere without being absorbed
