Waves Flashcards
What are S seismic waves?
Transverse and only travel through solids
What are P seismic waves?
Longitudinal, fast and travel through solids and liquids
What natural disaster are seismic waves produced from?
Produced by earthquakes
What are the 2 types of Seismic waves?
P waves and S waves
Are ultrasonic waves ionising?
Waves are non-ionising
Where are ultrasonic waves partly reflected?
Ultrasonic waves are partly reflected at a boundary between two substances
What is the frequency of an ultrasonic wave?
Any sound with a frequency above 18000Hz is ultrasonic
What is the range a human ear can detect sound?
Detect sound in the range of about 20Hz to 20000Hz
What is the range a human ear can detect sound?
Detect sound in the range of about 20Hz to 20000Hz
What happens when a wave passes from one medium into another?
It can be refracted and change direction
What does refracted mean?
Where a wave meets a boundary between 2 different materials and changes direction
What is a medium?
An object or substance
What does the direction of refraction depend on?
♡Angle at which the wave hits the boundary
♡The materials involved
For light rays, the way in which a material affects refraction is called…?
The refractive index (measure of the extent to which light is refracted by a material)
Define refractive index?
Measure of the extent to which light is refracted by a material
What happens when light passes from air into glass?
The velocity of light decreases (slows down) causing the direction of the waves to change
What do sound waves have that all other waves have?
Frequency, amplitude and wavelength
When waves slow down (usually when entering the object) what happens to the wave?
It bends towards the normal (right angle) and pass through the block
What happens to waves when they pass from the glass block back to the air?
Their velocity (speed) increases and bends away from the normal, making the object appear to have shifted position
If a wave enters or leaves the object/medium at right angles to the surface (along the normal) what happens to the waves direction?
It doesn’t change direction
What is a wavefront?
An imaginary line that connects all the same points in a set of waves
What does the amplitude relate to in sound waves?
The loudness
What does the frequency and wavelength relate to in sound waves?
The pitch
How is sound made?
Sound in any medium is due to the VIBRATION OF THE PARTICLES THAT MAKE UP THE MEDIUM
What does the vibrations of particles in a solid sometimes cause?
In a solid these vibrations of particles to make sound can cause the ENTIRE OBJECT TO VIBRATE WITH THE SAME FREQUENCY AS THE SOUND WAVE
The conversion of sound waves to vibrations only happens over…?
A CERTAIN RANGE OF FREQUENCIES (number of waves per second)
What does the conversion of frequencies converted into sound depend on?
The structure of the object
What happens in the ear so we can hear?
In the ear, SOUND WAVES CAUSE THE EAR DRUM TO VIBRATE, this vibration is heard as sound
The limiting range of conversions limits what as humans?
The limited range of conversions is what limits HUMAN HEARING
What is the range of human hearing limited by?
THE FREQUENCIES AT WHICH THE EAR DRUM CAN VIBRATE
When a wave slows down, is it refracted towards or away from the normal?
TOWARDS THE NORMAL
When a wave speeds up, is it refracted away or towards the normal?
Refracted away from the normal
Can ultrasonic waves be heard by humans?
No as greater than 20kHz
What happens when ultrasonic waves meet a boundary between two different media?
The wave is partially reflected
How can we determine how far away a boundary is (ultrasonic wave) ?
By measuring the time taken for reflected waves to return to a detector
What are the uses of ultrasound in industry?
Detecting defects in materials without cutting into them. Defects could be manufacturing faults (cracks and air bubbles) or damage (corrosion)
What are the uses of ultrasound in medicine?
Pre-natal scanning, detection of kidney stones and tumours, produce images of damaged ligaments and muscles
What is echo or sonar sounding?
Use of ultrasonic waves for detecting objects in deep water and measuring the water depth
How do echo/solar sounding work?
Echo/ solar sounding is where an ultrasound pulse is sent into the water, which is then reflected back when it hits a surface
How do you calculate the distance travelled by a sound wave?
The time between the pulse being sent and the reflection detected. Distance = speed x time
What is the speed of sound in water?
1500 m/s (Meters a second)
What is the same thing that ultrasonic imaging and echo sounding do?
Both work by detecting the time between a transmitted pulse and a reflected pulse
Describe P-waves ?
☆Primary waves (p-waves)
☆Longitudinal
☆Travel at the speed of sound
☆Twice as fast as S-waves
☆Travels at different speeds through solids and liquids
What does the “s” stand for in S-waves?
Secondary
What do seismic waves tell us about earthquakes?
When seismic waves are produced, the difference in time between the arrival of P-waves and S-waves at different detectors can provide evidence about the location of the earthquake and the material they have travelled through
Name the 4 layers of the earth’s structure?
Crust, mantle, outer core and inner core
Name the state of the 4 parts of the structure of the earth?
●Crust is a solid
●Mantle is a solid
●Outer core is a liquid
●Inner core is a solid
Are scientists able to directly observe the earth’s interor?
No, even the deepest mines go only a few kilometres into the crust
How do scientists know that the interior of the earth has this structure?
Because of earthquakes
What are earthquakes?
A sudden movement between tectonic plates in the earth’s crust
What do seismic waves do during an earthquake?
Seismic waves carry energy away from the earthquake
How do seismic waves produced from earthquakes tell us about earth’s interior?
The seismic waves which carry energy away from the earthquake can be detected by seisometers in different countries, the waves patterns tells us info about earth’s interior
What way do seismic waves travel in an earthquake?
Seismic waves TRAVEL IN CURVED PATHS, due to density changes in the earth
What is the name given to parts of the earth where seismic waves can’t be detected?
S-wave shadow zone
What did the S-wave shadow zone tell scientists?
The S-wave shadow zone is due to the fact that S-waves can’t pass through a liquid, this told scientists that THE EARTH MUST CONTAIN A LIQUID CORE
Where can P-waves be detected during an earthquake?
Over almost anywhere over the earth’s surface
What is the name given to parts of the earth where P-waves can’t be detected?
P-wave shadow zones
Why are there P-wave shadow zones?
P-wave shadow zones are due to the fact that P-waves travel faster in solids than in liquids, P-waves slow down as they enter the liquid outer core and causes them to refract (change direction) and when they leave the outer core, this confirms that the outer core is a liquid
Sometimes P-waves can be detected in the shadow zones, what did this show scientists?
The earth contains a solid inner core
How did scientists work out the thickness of the crust, mantle, outer and inner cores?
From measuring seismic waves from thousands of earthquakes
What type of wave are electromagnetic waves (EM)?
Transverse
What is the same for all the EM waves?
All travel at the same velocity (speed of light) in air or in a vacuum
What do the two ends of the EM spectrum show?
EM spectrum extends from low frequency and low energy waves to high frequency and high energy waves
What light can human eyes detect?
Only capable of detecting visible light
The human eye can only detect visible light, what does this mean in terms of detecting EM waves?
Human eye can only detect a very limited range of EM waves
What does the wavelength of an electromagnetic wave affect?
●How it’s absorbed, reflected, refracted or transmitted
●This affects its uses
How many types of EM waves are there?
7 types:
●Radio waves
●Microwaves
●Infared waves
●Visible light
●Ultraviolet waves
●X-rays
●Gamma rays
Where do EM waves transfer energy from and to?
Transfer energy from the source of the waves to an absorber
Give an example of where EM waves transfer energy from the source of the waves to an absorber?
Microwave: Transfers energy from the source (oven) to the absorber (food)
Give another example to show how EM waves transfer energy from a source to an absorber?
Solar panels in space: energy from the source (sun) to the absorber (solar panels on space craft)
What happens when we pass white light through a prism?
Splits into a spectrum (seven colours of the rainbow 🌈 )
Starting with red all the way to violet, what is the frequency and wavelength of each end?
Red end of spectrum=lower frequency,longer wavelength
Violet end of spectrum=higher frequency, shorter wavelength
What does each colour of light have?
Different frequency and wavelength
What is the sentencd to remember the electromagnetic spectrum?
Raw Meat Is Very Unsanitary eXcept Giraffe
The EM spectrum starts from radio waves to gamma rays at the end, what happens to the frequency and wavelength?
●Frequency increases from radio waves to gamma rays
●Wavelength decreases from radio waves to gamma rays
What do scientists say about the electromagnetic spectrum?
It is a continous spectrum
Scientists call the electromagnetic spectrum a continous spectrum, what does this mean?
The cut-off point between one type of a wave and another is not always clear
All electromagnetic waves travel at the same speed in a vacuum, what is the speed?
300 million / 3x10^8 m/s
(Meteres per second)
Different materials absorb, transmit and reflect EM waves, but what happens to the waves depends on…?
THE WAVELENGTH
Examples:
●microwaves are absorbed by foods which contain water molecules but microwaves are reflected from metals
●Light waves are absorbed by black surfaces and reflected by shiny surfaces
Where are radiowaves used?
Television, radio, bluetooth
Why are radiowaves used for Bluetooth, television etc?
Because low energy waves, not harmful, makes them ideal for radio transmission
Where are microwaves used?
Satellite communications and to cook food
Why are microwaves used for satellite communication?
Travel in straight lines through atmosphere so ideal fir transmitting signals to and back from satellites
What are the uses of infrared?
Electrical heaters, cooking food, infrared heaters
How are infrared waves used to cook food?
Electrical heaters glow red hot as electricity flows, this transmits infrared energy which is absorbed by the food and converted back into heat
Where is visible light used?
Fibre optic communications
Why is visible light used for fibre optic communications?
Travels down optic fibre communications from one end to the other without being lost through the sides
Where is ultraviolet waves (UV) used?
Energy efficient light bulbs and sunbeds
Why are UV waves used for energy efficient light bulbs?
In EELBs UV waves are produced when it is excited by the electric current, these UV waves are absorbed by the coating on the bulb which fluoresces (ability to give off visible light after absorbing radiation)
Uses of x-rays?
Medical imaging and treatment
How do x-rays work in medical imaging?
X-rays able to penentrate(pass through) soft tissue but not bone. A photographic plate behind a person will show shadows where bones are
Gamma ray uses?
Tumour treatment and sterilising food
Why are gamma rays used to destroy tumours and bacteria?
As gamma rays are the most energetic of all electromagnetic waves and can be used to destroy tumours and bacteria
How are radio signals produced?
Caused by oscillations (vibrations) in electrical circuits. The frequency of the radio wave produced matches the electrical vibration
How are radio signals received?
When radio waves are absorbed by a conductor they may create an alternating current with the same frequency as the radio. When this vibration is induced (produced) in an electrical circuit it creates an electrical signal that matches the wave
Why is it called the electromagnetic spectrum?
Because they (the waves) are made up of oscillating (vibrating) electric and magnetic fields, which means we can generate the waves using electric (alternating current as its made up of oscillating charges)
What does changes in atoms and in the nucleus of atoms cause?
Can result in EM waves being generated or absorbed
What does the risk of damage from EM waves depend on?
Risk of damage from EM waves depends on TYPE OF RADIATION AND AMOUNT OF EXPOSURE
Give an example of where changes in atoms causes EM waves to be generated?
●Electrins moving between energy levels as a result of heat or electrical excitation generates waves such as infrared waves, visible light, UV waves, X-Rays
What do ultraviolet waves, x-rays and gamma rays do to the body?
If they carry enough energy they can have a hazardous effect on the human body
How do UV waves damage the bod?
UV waves cause skin to age prematurely and increase the risk of cancer
How do x-rays and gamma rays damage the body?
X-rays and gamma rays are ionising radiation, damage cells by ionising atoms if absorbed by nucleus of cell it can cause gene mutations and cancer
Why are microwaves suitable for cooking food?
Because they are easily absorbed by water
How does a lens form an image?
By reflecting light
What are the two types of lens?
●Convex
●Concave
Describe the shape of a convex lens?
Wider in middle than at edges
What happens to parallel rays of light when it enters a convex lens?
Parallel rays of light are brought to thr focal point/principal focus (point where parallel rays of light travelling through a lens meet)
What is the other name given to cover lenses?
As parallel rays of light entering a convex lens converge (come together) they are sometimes called converging lenses
What is the name given to the distance from the lens to the principal focus/focal point?
The focal length
Describe the shape of a concave lens?
Wider at edges than in the middle
What happens to parallel rays of light entering a concave lens?
They are spread out
When parallel rays of light enter a concave lens it spreads out, what does this make the rays appear to be coming from?
The principal focus on the same side of the lens that they originated
What are concave lenses also called?
Diverging lenses as when light enters a concave lens it diverges (spreads out)
