Topic 2 - Waves and the Electromagnetic spectrum Flashcards
What do waves transfer
energy and information
what are the differences between longitudinal and transverse waves
transverse waves are perpendicular to the direction of travel
longitudinal are parallel and trevel in a series of compressions and rarefactions
Give some examples of transverse and longitudinal waves
Transverse - light, S waves and all EM waves
Longitudinal - sound, P waves
what are the two equations used to find wave speed
frequency x wavelength
distance / time
How do you measure the velocity of sound in air
Using an oscilloscope -
attach 2 microphones to find wavelengths of sound wave generated.
-the wavelength is the distance between the microphones
-frequency is the signal generator
How do you measure the velocity of waves on a water surface
Using a strobe light and a signal generator attached to a dipper so waves are at set frequency
-distance between each shadow line is a wavelength
What is refraction
When a wave changed direction at a boundary
What happens when a wave goes from 1 material to another
- When a wave hits at an angle it causes a change of speed
- so when it hits a glass block for example it changes direction
- when entering it bends towards the normal
- when leaving it bends away from the normal
what does it mean if a wave is reflected
when a wave is neither absorbed or transmitted but sent back away from the second material
eg) echos
What are the effects of waves being transmitted or absorbed
- waves transfer energy to energy stores - absorption
- when waves carry on travelling through a new material they are transmitted
what are the parts of the human ear
sound waves travel down
- ear canal
- osscicles
- through semi circular canal
- cochlea
- auditory nerve to brain
how are sound waves converted to vibrations in solids (in the ear)?
When sound waves hit the cochlea it causes them to vibrate and turns them into vibrations which go down the ear. The structure and shape of our eardrum effects this
Why can the human ear only detect a certain range of frequencies
Because the frequencies above 20,000 Hz and below 20 Hz are too high/low pitch to be detected
How can you calculate the depth of water with time and wave velocity
- send signals from boat and measure how long it takes to come back
- half this time as we only want one way
- use wavelength = wavespeed x time
What is ultrasound
any frequency above 20,000 Hz
How is ultrasound used in sonar
It can be used in echo-sounding to detect how deep the oceans are
How is ultrasound used in foetal scanning
As ultrasound can pass through the body, it can reflect back off the womb and skin of the foetus
these signals can be detected on a computer to produce an image
What is infrasound
Any frequency below 20Hz
Name some uses of infrasound
- animal tracking for whales and elephants
- detect natural disasters such as earthquakes from their seismic waves- these are monitored by scientists
What type of wave are seismic waves
infrasound
What is the difference between P and S waves
P waves - longitudinal, travel through solids and liquids and and faster than S waves
S waves - transverse, travel through Solids and are slower than P waves
How do seismic waves help us investigate the earths core
Only Pwaves can travel through the earths outer core which means it must be a liquid/ molten and the earths core is Solid.
What is the law of reflection
Angle of incidence = angle of reflection
What is total internal reflection
- Depends on the critical angle
- only happens when angle of incidence is larger than the critical angle so no light comes out
What is the difference between specular and diffuse reflection
Specular- waves are reflected in a single direction by a smooth surface so you get a clear reflection
Diffuse- On rough/matt surfaces, waves are reflected in all directions as the normal is different for each incident waves
What is white light
A mixture of all different colours of light which have different wavelengths
Why do surfaces appear to have different colours in terms of differential absorption
Because it depends on which wavelengths of light are reflected
eg) red apple reflects red
How do filters make coloured light
They filter out different wavelengths of light in terms of transmission and absorb these colours
eg)red light»» blue filter =black
How does viewing of different coloured objects differ in other colours of light
with red apple, green pear, blueberry
- red apple- blue and green light makes black, red stays red
- green pear- blue makes blue, green=green, red light=black
- blueberry- blue= blue, green= cyan red=black
What does the power of a lens mean
As the power of a lens increases, it bends light through a greater angle
How does the focal length effect the shape and power of a lens
more powerful= more strongly converging light=shorter focal length
Power of a lens increases with its curvature
How does a converging lens refract light
-light rays hit a convex lens and refract/bend towards the normal
-and when leaving the lens come together to form a real image on a screen
(Positive power)
How does a diverging lens refract light
- as the light rays enter they spread out/ diverge and create a virtual image which appears to come from a different direction
- and if we trace the rays back we find the virtual principal focus
How do we find the focal length
distance between the virtual principle focus and lens
What are all 7 Electromagnetic Waves
Radio, micro, infrared, visible light, ultraviolet, X-ray, Gamma
Name some features of EM waves
Transverse
Travel at same speed in a vacuum
Transfer energy from source to observer
Higher frequency = more energy transferred
How do we group EM waves
based on there frequencies and wavelengths
What effects energy transfer in EM waves
Higher frequency = more energy transferred
What range of EM waves can our eyes detect
Visible light
What is the order of the visible light spectrum
Red, orange, yellow, green, blue, indigo, violet
How do velocities of EM waves differ in different substances
- Vacuum all the same
- Other materials - shorter the wavelength the more it bends to change direction and the slower it is
eg) light travels slower in denser materials, radio not as much
frequency is the same + wavelength slower
Name some different ways EM waves are absorbed and transmitted
- Radiowaves arent absorbed by the body
- Gamma can be absorbed by deeper tissues
- UV is absorbed by skin and can cause damage to cells
- UV is absorbed by Earths atmosphere
- Some materials absorb light wavelength of one colour but not others causing them to be a certain colour
How are radiowaves affected by travelling through different substances
- transmitted through body
- not harmful if absorbed
- can be reflected and change direction
Name some uses of Radiowaves
communication and broadcasting
Name some uses of Microwaves
microwaves, communication by satellite
Name some uses of Infrared
T.V remotes, infrared cameras
Name some uses of Visible Light
photography film, cameras
Name some uses of UV
fluorescent lamps, security pens
How are radiowaves produced and detected by electrical circuits
Radiowaves are produced by oscillating charges creating alternating currents.
This energy is transferred to the electrons in the material of the reciever
How does the intensity and wavelengths of emitted radiation depend on the temperature of the body
- When intensity increases rapidly for shorter wavelengths. The rate an object radiates EM radiation affects its temperature
- object at a constant temperature radiates and absorbs the same average power
Name a use of X-rays
airport security scanners
Name some uses of gamma rays
sterilising medical instruments, cancer treatment
How does the danger of EM radiation depend on its frequency
The higher the frequency the more dangerous it is because it transfers more energy
What are the harmful effects of infrared
infrared can cause burning
Danger of UV
skin cancer
Dangers of X-Ray
too much exposure puts you at risk of cancer
Dangers of Gamma
damages cells and causes mutations which can lead to cancer
