5) Light & The Electromagnetic Spectrum Flashcards
What wave type are all electromagnetic waves?
Transverse
What speed do all EM waves travel at in a vacuum?
The same speed
What are the 7 types of EM wave?
Gamma X-ray Ultravoilet Visible Infrared Microwave Radio waves
Which EM wave carries the most energy?
Gamma rays
How do gamma rays’ wavelength and frequency compare to the other EM waves?
Shortest wavelength
Highest frequency
How do radio waves’ wavelength and frequency compare to the other EM waves?
Longest wavelength
Lowest frequency
What happens to the freqquency as wavelength increases?
Frequency decreases
What are uses of gamam rays?
Medical imaging and therapy
Astronomy
Sterilisation
Food preservation
What are risks of gamma rays?
Extremely penetrating and damaging to living tissues and cells
What do we use gamma rays to destroy?
Bacteria
Tumours
What are uses of x-rays?
Medical and industrial imaging
Treating cancer
Security purposes
Why are x-rays used to scan the body?
X-rays penetrate soft materials (body tissue)
Bones are dense and absorb x-rays
What are risks of x-rays?
Highly ionising (can damage body cells)
How can you shield yourself from x-rays?
Place metals or lead between yourself and the x-rays
What are risks of ultraviolet light?
Skin burns
Skin cancer
Cataract formations in the eye
What are uses of ultraviolet light?
Medical and forensic photography Air purification Water disinfection Medical therapy Detecting fake notes
What do UV photons do to atoms?
They give energy to atoms causing them to release visible light
What are risks of infra-red radiation?
Serious skin burns if emitted from high intensity sources
What do infra-red lights do to food?
Excite the particles causing an increase in temperature
What are uses of infra-red light?
TV controls
Security purposes
Body heat detectors
What are uses of microwaves?
Satellite communications
Phone signals
Heating food and drink
Why are microwave used for satellite communications?
They have a high enough frequency to penetrate the Earth’s atmosphere
Travel in straight lines
What are risks of microwaves?
Humans are made up of water so exposure could be harmful
How do we use safety with microwaves?
Using protective shielding
What molecules can microwaves transfer energy to?
Water molecules
What are risks of radio waves?
High intensities can cause internal heating of tissue
What are uses of radio waves?
Radio and TV communications
What does radio waves’ long wavelength mean?
They can be transmitted around the Earth’s surface and buildings without interference
How can electromagnetic waves be produced?
Electrical circuits
Changes in atoms
What do changes in atoms produce?
Radiation of lots of different frequencies
How are EM waves produced in electrical circuits?
Oscillations can produce radio waves
What happens when radio waves are absorbed?
They can create an AC current with the same frequency as the radio wave itself
This means radio waves can lead to oscillations in an electrical circuit
How are EM waves produced in changes in atoms?
Changes in the nuclei can result in EM waves being generated or absorbed over a wide frequency range
Where do gamma rays originate from?
Changes in the nucelus of an atom
What are the 7 colours of the visible light spectrum?
Red Orange Yellow Green Blue Indigo Violet
Why can we use visible light in optical fibres?
It can be totally internally reflected
What are uses of visible light?
We use visible light to see the world
Fibre optics
What determines the opacity of an object?
Whether light is absorbed, reflected or transmitted
What are the 3 opacities?
Opaque
Translucent
Transparent
What happens to light to make objects translucent?
Light is transmitted but rays are scattered
What happens to light to make objects opaque?
Light is either reflected or absorbed
What happens to light to make objects transparent?
Light is transmitted without scattering rays
Which colour has the lowest frequency and longest wavelength?
Red
Which colour has the highest frequency and shortest wavelength?
Violet
What are the two ways light can be reflected?
Diffuse
Specular
What is diffuse reflection?
When light is scattered by a rough surface
What is specular reflection?
Light is reflected in a single direction by a smooth surface
What is the colour of an opaque object when all of the wavelengths are reflected equally?
White
What is the colour of an opaque object when all of the wavelengths are absorbed?
Black
What happens to wavelengths when an object has a particular colour?
It reflects all of the particular wavelength (colour)
Absorbs all other wavelengths
What do colour filters do?
Absorb certain wavelengths and transmit other wavelengths
What is internal reflection?
When light speeds up when entering a less optically dense medium
Some light is refracted and some light is reflected
What happens if the angle of incidence is the same as the critical angle?
Light will travel along the boundary of the 2 mediums
What is total internal reflection?
If the angle of incidence exceeds the critical angle all of the light will be reflected
How does a lens form an image?
By refracting light
What are the main types of lens?
Converging (convex)
Diverging (concave)
How does the power of a lens increase?
When the difference between the middle thickness and edge thickness increases
How does a convex lens’ power increase?
Thicker middle comapred to edges
How does a converge lens’ power increase?
Thinner middle compared to edges
What is the equation for power of a lens?
P = 1 / f Power = 1 / focal length
How does the focal length size affect the power?
Larger focal length = lower power
What is the focal length?
The distance between the lens and the principle focus
How does a lens form an image?
By refracting light
What does a convex lens look like?
Wider in middle than edges
Where is the principal focus of a convex lens?
Where all rays hitting the lens parallel to the axis meet
What does a converge lens look like?
Wider edges than middle
What happens when parallel light rays enter a concave lens?
They disperse
Where is the principal focus of a concave lens?
Tracing back along the path of the dspersed rays, they will come from the principal focus behind the lens
What type of images can convex lenses produce?
Real or virtual
Whattype of images can concave lenses produce
Only virtual
What is the equation to calculate the magnification a lens produces?
Magnification = image height / object height
What is the unit for magnification?
It is a ratio
No units
What can we not project onto a screen?
Virtual images
Where does a virtual image appear?
On the same side of the lens to the object
Where does a real image appear?
On the other side of the lens to the object
How do you draw ray diagrams?
1) Draw the principal axis (horizontal line straight through middle of lens)
2) Use correct lens symbols
3) Mark princiapl focus on either side of the lens, draw on dot on principal axis and label it F
4) Mark position of the object as an arrow standing on principal axis
5) Draw light rays
What is the symbol for convex lenses in ray diagrams?
Double headed arrow
What is the symbol for concave lenses in ray diagrams?
Inverted double headed arrow
How do you draw a convex lens ray diagram?
1) Draw line from top of object to lens
2) From point on lens draw second line through principal focus on other lens side
3) Draw third line from top of object straight through mid of lens
4) If lines meet on other lens side this forms a real image
5) Draw image as a vertical arrow connecting the point lines meet to principal axis
6) If lines do not meet this forms a virtual image
What do all objects emit?
Radiation
Where will an object always transmit heat to?
Hotter area to colder area
When is the rate of temperature emission higher?
When an object’s internal temperature is higher than the environment’s temperature
What does a body at constant temperature do with radiation?
Absorbs radiation at the same rate it emits radiation
What is the process of the greenhouse effect?
1) Sun emits short wavelength infrared radiation
2) Earth absorbs some radiation but long wavelength is reflected
3) Greenhouse gases can’t absorb frequency emitted by sun but can absorb longer wavelength radiation
4) Gases re-radiate energy towards Earth
5) Earth’s temperature increases
What length wavelengths does the sun emit?
Short wavelength infrared radiation
What length wavelength does the Earth reflect?
Long wavelength radiation
What are 3 types of greenhouse gases?
Methane
Carbon dioxide
Water vapour
What does the temperature of a body (object) depend on?
Rate of absorbtion and rate of emission of radiation
What factors affect the rate of emission and absorbtion?
Surface area
External temperature
Internal temperature
How much solar energy per square metre falls on Earth?
340 Watts
What percentage of solar energy is reflcted to space?
29%
What percentage fo solar energy is absorbed in the atmosphere?
23%
What percentage of solar energy is absorbed at the surface?
48%
Why can infra-red radiation travel through space?
It does not need a medium
What can be said about the amount of energy absorbed and emitted by the sun?
It is in balance
