Waves Flashcards
What direction do waves transfer energy?
They transfer in the direction they are travelling
What are Transverse waves?
The oscillations of the waves are perpendicular to the direction of travel
- All electromagnetic waves (light)
- Ripples and waves in water
- a wave on a string
- S waves
What are Longitudinal waves?
The oscillations of the wave are parallel to the wave of travel
- Sound waves in air (ultrasound)
- Shock waves (some seismic waves)
- P waves
What is frequency?
the number of complete waves passing a certain point per second
- Hertz (Hz)
What is Wave speed?
the speed at which energy is being transferred
OR
the speed the wave is moving at
What is an oscilloscope?
A device for viewing oscillations on a screen
- measure the speed of sound
How do you use an oscilloscope to measure the speed of sound?
- Set up an oscilloscope connected to 2 microphones near a speaker. So detected waves at each microphone are shown as seperate waves
- Start with both mics next to the speaker, then move one away slowly until the 2 waves are aligned on display, but moves 1 wavelength apart
- Measure the distance between the mics to find the wavelength
- Use wave speed equation to find wave speed (should be around 330 m/s)
What can happen to a wave when it arrives at a boundary between 2 different materials?
- Can be Absorbed
- Can be Transmitted
- Can be Reflected
What happens if a wave is absorbed by the material it’s crossing into?
It transfers energy to the material’s energy stored
- microwave
What happens if a wave is transmitted through the material it’s crossing into?
The waves carry on travelling through the new material, often leading to refraction
What happens if a wave is reflected on the material it’s trying to cross into?
What does a wave being absorbed, transmitted and reflected depend on?
- wavelength
- properties of the materials involved
What is the rule applies to all reflected waves?
Angle of Incidence= Angle of Reflection
What is the angle of incidence?
the angle between the normal and the incoming ray
What is the angle of reflection?
the angle between the normal and the reflected ray
What is the normal
a line that is perpendicular (at right angles) to the surface at the point of incidence
- usually shown as a dotted line
What is the point of incidence?
the point where the wave hits the boundary
What is Specular reflection?
a wave is reflected in a single direction by a smooth surface
- mirror
What is Diffuse reflection?
a wave is reflected by a rough surface, reflected rays are scattered in lots of different directions
- piece of paper
Why does Diffuse reflection occur?
- normal is different for each incoming ray, angle of incidence differs
- surface appears matte, no clear reflection on the surface
Are EM waves transverse or longitudinal waves?
Transverse waves
What are Electromagnetic waves?
Transverse waves that transfer energy from a source to an absorber
- travel at the same speed through air or a vacuum
- grouped into 7 basic types based on wavelength + frequency
What is a vacuum?
an area with no matter/particles
What is the Electromagnetic spectrum order?
Radiowaves
Microwaves
Infrared radiation
Visible light
Ultraviolet
X-rays
Gamma rays
As the EM spectrum goes down does it increase or decrease in frequency and wavelength?
It has an increasing frequency and a decreasing wavelength
Radiowaves- low frequency, long wavelength
Gamma rays- high frequency, short wavelength
What is refraction?
When a wave crosses a boundary between materials at an angle, and changes direction
What does the amount a wave is refracted by depend on?
- ## How much the wave speeds up or slows down (depends on density of the 2 materials, higher density= slower the wave travels through)
What is FAST
F- fast
A- away
S- slow
T- towards
If a wave crosses a boundary and slows down, it will move towards the normal
If a wave crosses a boundary and speeds up, it will move away from the normal
What changes when a wave is refracted?
The Wavelength of a wave CHANGES but Frequency STAYS THE SAME
What happens to a wave if it is travelling along the normal?
- Changes speed
- NOT refracted
What is Optical density of a material?
A measure of how quickly light can travel through said material
the higher Od, the slower light waves travel through
What are EM waves made up of?
Oscillating electric and magnetic fields
How are Radiowaves produced?
- Use an alternating current in an electrical circuit
- Transmitter- charges electrons to oscillate to create radiowaves
- transmitted radiowaves are recieved by the Receiver
- energy carried by wave is transferred to receiver electrons
- causes electrons to oscillate and if its a complete circuit, creates AC current
- This current has the same frequency as the radio wave that generated it
What are uses of Radiowaves?
Wavelength= longer than 10cm
- Long-wave radio-> 1-10km wavelength, bend/diffract around curved surface of earth, hills, tunnels etc, Can be recieved even if receiver isn’t in line of sight
- Short-wave radio-> 10-100m wavelength, long distances, reflected from ionosphere (electrically charged layer of earth’s upper atmosphere)
- Bluetooth-> sw radio waves, sends data over short distance without wires
- Medium-wave signals-> can sometimes reflect from ionosphere (if they are short), depends on atmospheric condition + time of day
- TV and FM radio transmission (sw radio waves), direct signal of transmitter (no bending or long distance travel)
- communication
What are uses for Microwaves?
- Communication between satellites (tv signal, satellite phones): Passes easily through earth’s atmosphere
- Microwave ovens: microwaves absorbed by food molecules, penetrate a few cm before being absorbed, transfers energy, heating water thus heating food
How does satellite TV work?
- Signal from transmitter is transmitted into space
- picked up by satellite dish (receiver), transmits signal back down to earth
- received by satellite dish on the ground (slight time delay due to long distance of travel)
What are uses for Infrared radiation?
- Infrared camera: detect IR radiation and monitor temperature, turns temp into electrical signal, displayed on the screen as a picture. Hotter= brighter
- Cooking food: causes objects to get hotter, ie toast from toaster
- Electrical heaters heating a room: long piece of wire that heats + glows with a flowing current, emits high IR radiation, absorbed by objects and the surroundings and air. Energy transfers to their thermal energy stores, causing their temp to increase
What objects is Infrared radiation emitted by?
All objects
- the hotter the object, the more radiation given out
What are fibre optic cables?
Thin glass or plastic fibred that carry data (from telephones, computers etc) over long distances as pulses of visible light
- reflection, bounce back and forth until end of fibre
-visible light
- not easily absorbed or scattered
What are uses for UV radiation?
Fluorescence-> UV is absorbed, visible light is emitted, looks bright
Energy efficient lights, used for long periods (classrooms)
Security pens (ink only glows under UV light)
UV radiation from Sun-> gives tan
Tanning salons-> UV lamps, artificial suntan. Overexposure=dangerous
What are uses of X-rays and Gamma rays in medicine?
X-ray photos-> broken bones
Easily pass trhough flesh, not dense material like bones/metal
Treat cancer (radiotherapy), high doses kill all living cells, carefully directed, avoid killing too many healthy cells
Gamma-> medical tracer, pass trhough the body undetected
can be harmful- wear lead aprons, lead screen, stand outside room to keep exposure to minimum
How can EM radiation be harmful?
