Waves Flashcards
(31 cards)
What happens when a wave travels through a medium
The particles of the mesium oscillate and transfer energy between each other but overall the particles stay in the same place-only energy transferred
What is amplitude of the wave
The maximum displacement of a point on the wave from its undisturbed posiition
What is wavelength
Distance ebtwwen the same point on two adjacent waves
What is frequency
Frequency is the number or complete waves passing a certain point per second. Measured in hertz (hz) per second
How to calculate period
1
T= ——-
F
What direction do oscillations travels in tranverse waves provide examples
In transverse waves the oscillations are perpendicular (90°) to the direcrion of energy transfer
All electromagnetic waves (light), ripples through water, guitar string
What direction do oscillations travels in longitudinal waves provide examples
In longitiudinal waves the oscillations are parallel to the direction of enrgy transfer
Sound waves in air
How to calculate wave speed
V = fλ
How do you use an oscilloscope
1) set the oscilloscope so the detected waves at each microphone are shown as seperate waves
2) start with both microphones next to the speaker, then slowly move one away until the two waves are aligned on the display but have moved one wavelength spart
3) Measure the distance between the microphone to find wavelength
4) Use V=fλ to find speed of the waves through the air- f is what you set the signal generator to
5) The speed of sound is 330m/s check your results to compare
Required practical: How to measure the speed of water using a ripple tank
1) use a signal generator attached to the dipper of a ripple tank you can create water waves at set frequency
2) Turn off the lights and turn on a lamp. You should see the wave crests as shadows on the screen below the tank
3) The distance between each shadow line = one wavelength. Measure the distance between shadow line that are 10 wavelengths aprt then divide by 10 to find average
4) Use V= Fλ to calculate wave speed
5) The set up is suitable for investigating waves, because it alllows youn to measure the wavelength without disturbing the waves
Required practical: How to use wave equation for waves on strings
1) place a signal generator on a bench with a vibration transducer to its side attached to a string in a pulley system with a hook with masses
2)Adjust the frequency of the signal generator until there is a clear wave on the string. F will depend on length between the pulley and transducer and the masses you use
3) Measure the wavelength. Best way is to measure multiple wavelengths at once using a ruler then divide by the number of wavelengths to get an mean half wavelength then double to get the full wavelength
4) Frequency depends on what the signal generator is set to
5) find speed using V = Fλ
What happens when a wave is absorbed,transmitted or reflected
Absorbed: the wave transfers energy to the second materials energy store. It is often transferred to thermal.
Transmitted: waves go through the new material then carries on the travelling through the new material often leading to refraction. This is used in communications or lenses in cameras
Reflected: Incoming rays are neither absorbed or transmitted but sent back from the second material. This is how echoes are created
Properties of EM waves
Transverse wave
Travel at the same speed through air ir a vacuum (space)
Vary in wavlength 10^-15 to 10^4
Range in frequencies throught the spectrum- radio low - gamma high
Travel at different speeds in different material
All the different waves on the EM spectrum
Radio waves
Micro waves
Infared waves
Visible light
Ultra voilet
X-rays
Gamma rays
Properties of radio waves
10^-4m
Low frequency
Properties of gamma rays
10^1-15
High frequency
What is refraction
1) When waves cross a boundary between two materials it changes speed
2) If waves hit along the normal only speed changes. If it hits at an angle only direction changes
3) The waves bend toward the normal (slows down)- the wave bends away from the normal (speeds up)
4) Higher the optical density the, the slower the light travels
5) wavelength only changes, frequency stays the same
How do ray diagrams show the path of a wave
1) Draw a boundary between your 2 materials and the normal. It should be perpendicular (90°) to where the wave will hit the boundary.
2) Draw an incident ray that meets the normsl at the boundary
3) Angle between the incident ray and normal is the angle of incidence.
4) Draw the refracted line on the other side of the boundary
5) Angle of refraction is the angle between the refracted ray and the normal
6) If the second material is optically denser than first , the refracted ray bends towards the normal (smaller angle of refraction then the angle incidience).
If the second material is less optically dense then the first, the refracted rays bend away from the normal (angle of refraction is larger than the angle of incidence).
How to use wave front diagrams
1) Wave front is a line showing all of the points on a wave that are in the same positions as each other after a given number of wavelengths
2) Wave crosses the boundary at an angle, only part of the wave front crosses the boundary at first. If its travelling into a denser material, that part travels slower then the rest of the front
3) By the whole time the whole wave front crosses the boundary, the faster the part of the wave front will have travelled further than the slower part of the wave front
4) The difference in distance travelled by the wave front causes the wave to bend
How are radio waves made by an oscillating charge
1) Em waves made up by an oscillating charge and magentic field
2) alternating currents make up the oscillating charge. As the charges collide they produce oscillating electric and magnetic fields, EM waves.
3) Frequency of waves produced will equal to the frequency of alternating current.
4) A transmitter in which charges oscillate to create radio waves reach a reciever to be absorbed. The energy carried by the waves is transferred to the electrons in the material of the reciever.
5) The electrons oscillate and if the reciever is part of a complete electrical circuit, an alternsting current will be produced.
6) Current has the same frequency as the radio waves that generate it
How are radio waves used for communication
Long-wave radio waves can diffract around the curved surface of the Earthand around hills,tunnels etc-radio waves can be recieved even if the reciever isn’t in line of sight
Short wave radio waves like long waves be recieved at long distances from the transmitter. They are reflected by the ionsphere-electrically chatged layer in the Eatths upper atmosphere
Bluetooth uses short wave radio waves to send data over short distances between devices.
Medium-wave signals can reflect the ionsphere, depending on atmospheric conditions
TV and FM radio transmisisons have very short wavelengths must be in direct sight of the transmitter.
How are microwaves used by satellites and for ovens
The transmitter sends microwaves to pass through the water atmosphere of the Earth easily to the satellite reciever dish where it transmits a signal back to the Earth recieved by another satellite dish.
In microwave ovens, the microwaves are absorbed by water molecules in food causing the water moleucles to heat up. It then transfers energy to the rest of the molecules in the food through heating which cooks the food.
How are infared waves used
Infared cameras can be used to detect infared radiation and monitor temperature. The camera detects the IR radiation and turns it info an electrical signal displayed on a screen as a picture. The hotter the object the brighter it is.
Food can be cooked by absorbing IR radiation-it gets hotter
Electrical heaters contains a long piece of wire that heats up when a current flows through. The wire emits IR radiation and the emitted radiation is absorbed by objects and the air- energy transferred by the IR waves to the thermal energy stores of an object
How do fibre optic cables use visible light
Optical fibres are thin pieces of glass or plastic fibres that carry data over long distances as pulses or visible light.
This happens due to reflection - light rays are bounced back and forth until they reach at the end of the fibre.
Visible light is used because it is easy to refract light enough so it remains in the fibre and isn’t easily absorbed or scattered as it travels along the fibre.
