SP5 Light And The Electromagnetic Spectrum Flashcards
What is a ray diagram
It’s a way of modelling what happens when light is reflected or refracted
What’s a normal
A line drawn at right angles to the barrier/mirror
What are the incident angles
The incident angle is the angle between the normal and incident Ray - reflected Ray’s are always measured from the normal too
What’s the law of reflection
When waves are reflected, the angle of reflection is always equal to the angle of incidence
What’s refraction
When a wave changes direction due to entering a different material -
when light meets the interface along the normal/ at right angles there is no change in direction
How does light refract
It bends towards normal of it goes into a medium when is travels more slowly
Bends away from normal it it goes into normal where is travels faster
When the incidence angle increases the refraction angle…
Increased until the light passes along the interface
What’s total internal reflection
When the angle of incidence increases so much light is reflected inside glass -
What’s the critical angle
The angle of incidence when total internal refraction starts to happen
When does total internal reflection occur
At angles of incidence greater than the critical angle - light is totalling reflected by glass block
What happens when the critical angle is equal to the incidence angle
The refracted light passes along the interest with some light being reflected
What is diffuse reflection
When a material has a rough surface, light is scattered in all directions
What’s specular reflection
On very smooth surfaces such as mirrors, light reflects evenly
What is white light
The light from the sun, it’s actually made up of different colours that our eyes see as white
It can be split up into the colours of the visible spectrum using a prism
Why would a red object look red
It would look red because it reflects red and absorbed all the other colour
A white object looks white Becuase it reflects all of the colours
What are filters
Pieces of transparent material that absorb some of the colours in white light, etc a blue filter transmits blue light and absorbs all other colours
What’s a lens
A piece of transparent material shaped to refract light in particular ways
What does the power of th lens show
How much it bend light that passes through , a more powerful lens is more curved and bends more light
What’s a converging lens
Is fatter in the middle than the edges, it makes parallel Ray’s of light converge to a focal point
What’s the focal length
The distance between the focal point and the centre of the lens
What’s a diverging lens
Is thinner in the middle that the edges
The focal point is the point from when the Rays seem to be coming after passing through the lens (it’s where the rays are originally parallel
What can a converging lens be used for
Focus Ray’s of light on to s screen. An image can be projected in to a screen in this way - we call this a REAL IMAGE
What’s a real image and how is it made
When an image can be projected onto a screen and can only be formed by light rays that come together
What’s a virtual image and how is it formed
An object close to a converging lens will form a virtual image
It can not be projected onto a screen and appears to be on the same side of the lens as the object - it’s upright and Magnified
What kind of image of image do diverging lens produce
Virtual images that’s are the same way up and diminished and closer to the lens than object
What are the frequencies of light that are eyes can detect also known as
Viable light - different frequencies cause us to see different colours
Tell me about colour frequencies
Red is a lower frequency
Blue is a higher frequency
What animals can detect electromagnetic waves with high frequencies than visible light
Birds
What type of waves are em waves
Transverse
What speed to em waves travel at in a Vacuum
3x10^8 m/s
Tell me about infra red
All objects emit infrared radiation, hotter the object - the more emitted
Who discovered infrared
William Herschel when he put dark coloured filters on telescope to observe sun safely and noticed that different colours made his telescope different temperatures
He used this idea to split sunlight from a prism and out a thermometer on each colour - also measured a temperature just beyond red of the spectrum (no visible light)
Blue was coldest
Red was hottest
Tell me in order the seven colours in the visible spectrum
Red, orange, yellow, green, blue, indigo, violet
Or
ROY G BIV
What em waves have frequencies lower than visible light
Microwaves and radio waves
What em Ray’s have higher frequencies that visible light
X Ray’s and gamma rays
In the em spectrum higher frequency waves have…
Shorter wave lengths
Lower frequencies have King wave length
Tell me the order of the em spectrum
Highest frequency Gamma rays X Ray's Ultraviolet Visible light Infrared Microwaves Radio waves Lowest frequency
What are most telescopes like
Curved mirrors to focus the em radiation to a central sensor
What used are there for visible light
Light bulbs - emit visible light
Cameras detect it and record images
What are some used for infrared
Used for Tv remote controls
Information sent along optical fibres sent via infrared radiation
A grill or toaster transfers energy by IR to cook food
What are the uses of microwaves
Used for satellite transmissions eg mobile phone signals
Microwave ovens
What are some uses of radio waves
Used for transmitting radio broadcasts for tv programs
Controllers on the ground communicate with space craft using ratio waves
How are radio waves produced
By oscillations in electrical circuits
A metal rod can be used as an aerial to records radio waves
radio waves absorbed by metal and caused oscillations in electrical circuits
How do radio waves travel
In straight lines unless reflected or refracted - some frequencies of radio waves refracted by ionosphere (part of atmosphere)
If refracted at a suitable angle they can send them back to earth
What’s the part of the em spectrum that can’t be refracted by earths atmosphere
Microwaves
The higher the temperature the shorter the…
Wavelengths
The intensity(amount) of radiation emitted by an object increases as
It’s temperature increases
What is the power
The amount of energy transferred in a certain amount of times
What is power measured in
Watts (W) 1w=1j/s
What must a system do to stay at a constant temperature
Must absorb the same amount of power as it radiates
How much radiation does the earth absorb from the sun that reaches it
About half (51%)
What happens when sun rays are abseiled by earth
Re radiated as infrared radiation which can warm up the atmosphere
For earth to stay the same, it must…
Radiate energy into space at the same average rate it’s abstained
Name some greenhouse gasses
Methane
Carbon dioxide
What do greenhouse gases do
Absorb some energy from sun so earth is at a higher temperature
What is believed to be the cause of the greenhouse effect
Humans have upset the natural balance by emitting more greenhouse gases
Instead of Suns Ray’s being radiated back to space what do greenhouse gasses do
They absorb the energy that’s more than actsully needed
How could the temperature of earth decrease again
If greenhouse gases were removed from the atmosphere it would hold less energy
Tell me some uses of ultra violet
It transfers more energy than visible light, the energy transferred can be used to disinfect water by killing microorganism in it
Some materials absorb and remit uv at visible light called fluorescence that can be used for security markings as only visible when uv light shone on them
Tell me some uses of X-rays
Can pass through materials visible light can’t - like muscles and fat but bone absorbs some X-rays so can be used in medicine to take images inside body
Can be used to examine insides of metal objects and inspect luggage in airport security scanners
Tell me some uses of gamma rays
Transfer a lot of energy and and kill cells so used to sterilise surgical instruments and food
Used to kil cancer cells in radiotherapy which targets cancerous cells
Can be used to detect cancer by a chemical being injected into blood that emits gamma rays and collect inside cancer cells and a scanner locates the cancer by finding source of gamma rays
Gamma rays can pass through all materials in body
What’s is a danger of microwaves at certain frequencies
Certain frequencies of microwaves can hear water and could damage us by heating and killing cells as we are Mostly water
Tell me a danger about mobile phones
They use different microwave frequencies and emit and receive them but have not been around long enough to conclude any damage
How can infrared be a danger
Too much IR radiation can damage or destroy cells causing burns
How can UV RAYS cause be a danger
Too much can damage our DNA and too much exposure can lead to skin cancer
You can suffer snow blindness from too much Uv reflected from snow
How can we protect ourselves from Uv
Clothing, hats, sun cream with a high SPF, sunglasses
Tell me a danger of gamma and X rays
Have higher frequencies so can transfer more energy and excessive exposure can cause mutation in DNA to kill cells or cause cancer
How is electron magnetic radiation caused
By changes in electrons or the nuclei in atoms
Radiation can also cause chafed I atoms such as losing electrons to become ions
