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Light and the Electromagnetic Spectrum - Coggle Diagram
Light and the Electromagnetic Spectrum
Ray Diagrams
Intro
The normal is an (imaginary) dashed line which is perpendicular to the surface, and from which all angles are measured from
Incident Angle is the angle of the entering ray
Arrows show direction of light travelling
Reflected Angle is the angle of the exiting ray
Refraction
If entering a denser material, it bends towards the normal
If entering a less dense material, it bends away from normal
Total Internal Reflection
This occurs when the light is passing from a denser medium into a less dense medium (glass to air)
If the angle of incidence is equal to the critical angle, the refracted ray will pass along the boundary and not exit the medium
The critical angle is a unique angle for each two media (the critical angle for glass-air is different to glass-water)
For larger angles, the light internally reflects (following the above law of reflection) back into the glass
Glass to Air
If angle LESS than critical angle, light refracts away from normal
If angle EQUAL to critical angle, light passes along boundary
If angle MORE than critical angle, light reflects
Specular Reflection
Mirror reflection, following law of reflection, for a smooth surface (all light incident at the same angle all exit at the same angle)
Diffuse Reflection
Light hitting a rough surface – incident ray is reflected at many angles rather than just one
angle
Reflection
Incident angle = reflection angle
Angles are always measured from normal
Colour
Opaque Material
Objects appear to have a certain colour (e.g. ‘green’), as out of the incident white light only that certain colour light (green light) is reflected, all other colours are absorbed
Colour Filters
All other colours are absorbed, and only a certain colour is allowed to pass through - so only a certain wavelength is transmitted through the filter
Intro
Each colour is just a certain wavelength in visible light
All the colours together make up white light
Lenses
Convex Lenses
Focuses light inwards
Horizontal rays focus onto focal point
They are used for magnifying glasses, binoculars and to correct longsightedness, as it focuses the rays closer
(Look at Summary Notes for image)
Fatter at centre
Images
A real image is an image produced at the opposite side of the lens to the object
The above image for a convex lens is a real image
Virtual images appear to come from the same side of the lens to the object
This is if the object lies closer to the lens than the focal point (F)
(Look at Summary Notes for image)
Concave Lenses
“Caves” inward
Thinner at centre than at edges
Spreads light outwards
Light appears to have come from the focal point
Draw a faint line from focal point to point where the ray hits the lens
The ray exits the lens along the same direction as the faint line (shown by blue line)
Draw horizontal ray from top of object to lens
(Look at Summary Notes for image)
It is used to spread out light further
E.g. they are used to correct short-sightedness
As light is focused in front of the retina, so needs to be spread out slightly to be able to be focused onto retina
Intro
Focal Point is the point where all horizontal rays meet after passing through the lens
Power of the lens is the inverse of the focal length
Shorter focal length, greater power
Thicker lens means shorter focal length, so greater power
Focal Length is the distance between the lens and the focal point
EM Waves
Dangers of the EM Spectrum
Higher frequency EM waves have more energy, so exposure can transfer too much energy to cells, causing them to mutate and potentially damage them/causing cancer
Microwaves
Internal heating of body cells
Infra-Red
Skin burns
UV
Damage to surface cells and eyes, leading to skin cancer
X-ray/Gamma
Mutation or damage to cells in the body
Change in Atoms and Nuclei
Generate radiations over a wide frequency range
Be caused by absorption of a range of radiation
Temperature
If It absorbs more power than it emits –the temperature will increase
If it absorbs less power than it emits – the temperature will decrease
It must radiate the same average power that it absorbs to remain at a constant temperature
Temperature of the earth – this is maintained by the amount of energy received and emitted from the sun
Some is reflected by the atmosphere, most reaches the surface
The energy is absorbed and re-emitted as longer-length IR radiation
Short-wavelength Infra-red radiation from the sun reaches the Earth
This is mostly absorbed by the atmosphere (greenhouse gases, CO2 etc.) and keeps the Earth warm
Intro
EM waves do not need particles to move
In space, all waves have the same velocity (speed of light)
They all travel at the same speed in a vacuum
They can transfer energy from a source to absorber
Microwave source to food
Sun emits energy to Earth
They are transverse waves
Our eyes can only detect visible light
All electromagnetic waves transfer energy from source to observer
The waves contain energy, for example microwaves which transfers energy from source to food
Materials interact with EM waves differently depending on the wavelength
Glass can transmit visible light, reflect/absorb UV and IR
Relationships
As wavelength decreases, frequency must increase
As frequency increases, energy of the wave increases
As speed is constant for all EM waves in a vacuum
All Bodies emit radiation
The higher the temperature, the more intense (and more wavelengths) will be emitted
Uses of the EM Spectrum
Visible
Vision, photography, illumination
UV
Security marking, fluorescent lamps, disinfecting water
Radio
Communications, satellite transmission
They can be produced by oscillations in electrical circuits, or they can induce oscillations in electrical circuits
X-ray
Observing internal structure of objects, airport/medical scanners
Gamma
Sterilising food/medical equipment, treating cancer
IR
Cooking, thermal imaging, short range communication, optical fibres
Microwave
Cooking, communication
