Section 2: Waves & the Electromagnetic Spectrum Flashcards
What do waves transfer?
Energy and information
What is frequency?
Number of complete cycles of the wave passing a certain point each second
What is a period?
Amount of time it takes for a full cycle of a wave
How to calculate a period?
1/frequency
What is amplitude?
Maximum displacement of a point on a wave from its rest position
What is wavelength?
Length of a full cycle of a wave
Properties of transverse waves?
- Oscillate perpendicular to the direction that the wave travels
- Carry energy and information
Examples of transverse waves?
- Electromagnetic waves
- S-waves
- Ripples in water
Properties of longitudinal waves?
- Oscillate parallel to direction in which the wave travels
- Transfer energy and information
Examples of longitudinal waves?
- Sound waves
- P-waves
What can happen to a wave when it hits a boundary?
Absorbed
Reflected
Transmitted (either being refracted or not refracted)
What is reflection?
When the wave is reflected in the opposite direction
What is the law of reflection?
Angle of incidence = angle of reflection
What is refraction?
When a wave changes speed and direction as it crosses a boundary between two materials at an angle to the normal
What will happen if the waves slows down when it refracts?
Wave refracts —> slows down —> wavelength decreases —> wave bends towards normal
What will happen if the waves speeds up when it refracts?
Wave refracts —> speeds up —> wavelength increases —> wave bends away from the normal
What do electromagnetic materials do when refracted depending on density of material?
Slow down in denser materials
Speed up in less dense materials
What is total internal reflection?
When all light incident on a boundary is reflected back
What is the critical angle?
The minimum angle at which the total internal reflection occurs
What happens when the critical angle is larger than the angle of incidence?
The wave is mostly refracted, some reflected
What happens when the angle of incidence is larger than the critical angle?
There is total internal reflection
How do vibrations work in air?
- Vibrating object creates sound waves
- Sound waves travel as a series of compressions and refraction through air
How do vibrations pass through solids?
- Vibrating object creates sound waves
- Sound waves hitting solids cause the particles in the solid to vibrate
- Particles will then hit the next particles in line and so on - sound waves travel through the solid as these vibrations
How is sound heard?
- Sound waves reach ear
- This causes eardrum to vibrate
- These vibration cause other parts of ear to vibrate, allowing you to hear the sound waves
What is limited frequency range?
When conversion of sound waves to vibration in solids only occur over a certain frequency range
What are the limiting factors of frequency ranges in solid objects?
Size
Shape
Structure
What are ultrasound waves?
Sound waves with frequencies higher than 20,000Hz
What is ultrasound used for?
Medical scans e.g. pre natal scanning of foetus
Echo sounding (sonar) e.g. finding depth of water or locating objects in water
What are infrasound waves?
Sound waves with frequencies lower than 20Hz
What are P-waves?
Seismic waves that give evidence of the size of earths core and its structure
What are properties of P-waves?
Longitudinal waves
Travel through solids and liquids
What are S-waves?
Seismic waves that give evidence of the size of earths core and its structure
What are properties of S-waves?
Transverse waves
Can’t travel through liquids
What is the order of the colours in the visible light spectrum - starting with the largest wavelength?
Red
Orange
Yellow
Green
Blue
Indigo
Violet
What does colour depend on?
The wavelengths of light that are most reflected and those that aren’t
What do black objects do?
Absorb all wavelengths of visible light
What do white objects do?
Reflect all wavelengths of visible light equally
What do transparent and translucent objects do?
Transmit light
What is white light made up of?
All of the colours
What do colour filters do?
Transmit certain colours (wavelengths) and absorb the rest
What is a real image?
An image that is formed when the light rays from an object converge and meet each other and can be projected onto a screen
What is a virtual image?
An image that is formed when the light rays from an object do not meet but appear to meet behind the lens and cannot be projected onto a screen
What do converging/convex lenses produce?
Real OR virtual images
What do diverging/concave lenses produce?
ONLY virtual images
What happens as the lens gets more powerful?
Converges or diverges more strongly
Focal length shortens
In converging/convex lenses, what happens as the lens gets more curved?
The more curved the lens, the more powerful the lens
What type of powers do both lenses have?
Converging/convex = positive power
Diverging/concave = negative power
What is the order of the electromagnetic spectrum?
Radio waves
Microwaves
Infrared
Visible light
Ultra violet
X rays
Gamma rays
How to remember the electromagnetic spectrum?
Rachel
Makes
Indians
Very
Uncomfortable
X rays
Gamma rays
What happens as you continue down the EM spectrum?
Wavelength decreases
Frequency increases
What electromagnetic waves can our eyes detect?
ONLY visible light
What do electromagnetic waves do?
Transfer energy from source to absorber
Travel at same speed in a vacuum
How do objects link with the electromagnetic spectrum?
Objects continually absorb and emit EM waves
What happens to the body and EM waves at constant temperatures?
The object has a constant temperature…
BECAUSE IT ABSORBS THE SAME AVERAGE POWER THAT IT RADIATES
What happens to the body and EM waves at changing temperatures?
The objects temperature changes…
BECAUSE THE AVERAGE POWER IT ABSORBS IS MORE/LESS THAN THE AVERAGE POWER IT RADIATES
What happens with radiation in the daytime on Earth?
Earth absorbs more radiation than it emits
THEREFORE local temperature increases
What happens with radiation in the nighttime on Earth?
Earth emits more radiation than absorbed
THEREFORE local temperature decreases
Where is radiation emitted and absorbed on Earth?
Emitted - by atmosphere, clouds and earths surface
Absorbed - by atmosphere, clouds and earths surface
How are radio waves produced?
- Alternating current supplied (shown on oscilloscope)
- Electrons oscillate producing radio waves by the transmitter
- Emitted radio waves transfer energy
- Radio waves absorbed causing electrons in receiver to oscillate
- Alternating current of same frequency of radio waves induced in receiver
Uses of radio waves?
Broadcasting
Communications
Satellite transmissions
Uses of microwaves?
Microwave ovens
Communication
Satellite transmissions
Uses of infrared?
Cooking
Security systems
TV remote controls
Uses of visible light?
Photography
Illumination
Vision
Uses of UV waves?
Fluorescent lamps
Security marking
Detecting forged bank notes
Sterilising water
Uses of X-rays?
Medical X-rays
Airport security scanners
Uses of gamma rays?
Detecting and treating cancer
Sterilising food and medical equipment
Dangers of microwaves if there’s excessive exposure?
Heats up cells
Dangers of infrared if there’s excessive exposure?
Causes skin burns
Dangers of ultraviolet if there’s excessive exposure?
Causes damage to cells on surface of skin, can lead to skin cancer
Damages eyes, possibly causing eye conditions or blindness
Dangers of x rays if there’s excessive exposure?
Causes cell damage and mutation, can lead to cancer
Dangers of gamma rays if there’s excessive exposure?
Causes cell damage or mutation, can lead to cancer
How can exposure to radiation be reduced?
Spending less time with radiation - there are badges which change colour when your body shouldn’t be taking in anymore radiation
Distance - being far away from the radiation
Shielding - wearing the correct equipment e.g. lead lined gloves
Storage - led lined storage containers
WAVES CORE PRACTICAL: How can the speed of waves in air be found?
- Get a stopclock and a starter gun, make sure that both people in the experiment are 330m away from each other
- Start the stopclock when you see smoke coming out of the starter gun
- Stop the stopclock when you hear the sound of the starter gun being started
- Use speed = distance/time to calculate wave speed
WAVES CORE PRACTICAL: How can the speed of waves in water be found?
- Set up a ripple tank and place a piece of paper underneath
- Change the settings of the ripple tank to make the waves go as slow as possible but still be visible
- Using a ruler, measure the wavelength of the waves
- Using a stopwatch, time 10 seconds and see how many waves pass a fixed point that you’ve marked in the 10 second time frame
- Divide the number of waves that travelled past the point in 10 seconds by 10 to get the wavelength
- Use wave speed = frequency x wavelength
WAVES CORE PRACTICAL: How can the speed of waves in solid be found?
- Set up the apparatus: clamp stands with rubber bands, a metal rod going through the bands, a hammer and a device with a frequency app on it
- Once the rod is suspended by rubber bands, hit the rot with a hammer
- Measure the frequency of the wave using the frequency app on a device and note down the peak frequency of the wave
- Repeat steps 2-3, 3 more times to get accurate results and an average peak frequency
- Measure the length of the rod and multiply it by 2 to get the wavelength
- Use wave speed = frequency x wavelength
REFRACTION CORE PRACTICAL: How can refraction be investigated?
- Place a ray box on a piece of paper with a rectangular glass block on
- Trace around the block, then trace the incident ray and the emergent ray
- Remove the block and join the incident ray and emergent ray with a straight line (refracted ray)
- Draw a normal line where the ray entered the block and measure the angle of incidence and the angle of refraction (the angle between the normal line and the incident ray and the angle between the normal line and the refracted ray)
- Repeat step 4 but for the point where the ray exits the block.
REFRACTION CORE PRACTICAL: In conclusion, what 2 things can be gathered from the experiment investigating refraction?
- When the ray enters the block: angle of incidence > angle of refraction - meaning that the ray bends towards the normal going from air to glass so light is slower in glass than in air
- When the ray leaves the block: angle of refraction > angle of incidence - meaning that the ray bends away from the normal going from glass to air so light is faster in air than in glass
What are the uses of infrasound waves?
To investigate the internal structure of our planet - earthquakes produce very powerful seismic waves that can be classed as infrasound waves
How does white light form a spectrum when it passes through a prism?
- Light waves are refracted as they enter the glass because they are slowed down
- The spectrum is produced because different colours of light travel at different speeds in glass so are refracted differently
- The coloured light thus spread out to form a spectrum of white light - this is called dispersion
What is the focal length?
The distance between the centre of the lens and its principal focus
What is the principal focus?
The point where parallel rays meet after they pass through a lens
