Light and Electromagnetic spectrum Flashcards
What is a ray diagram used for?
A way of modelling what happens when light is reflected or refracted
What do the rays show in a ray diagram?
The direction the waves are travelling in
What is a normal?
Line drawn at right angles to the barrier or mirror
What is the incident ray and the reflected ray?
- Incident ray is the ray going towards the mirror or barrier
- Reflected ray is the ray that is reflected back
What is the law of reflection?
When the angle of reflection (measured from the normal) is equal to the angle of incidence (this then means that it has been reflected
What happens when a wave moves into a different material and what is this called?
It changes direction because they change speeds in different materials - called refraction
What is the interface?
Something that separates two different materials or matters - the boundary
What happens when light meets the interface at right angles?
It means it has moved along the normal and has no change in direction
Where does light travel faster, through air or through glass/water
Air
What happens when light passes through water or glass with small angles of incidence?
Most is refracted out but a small amount is reflected
What is the angle of refraction?
The angle measured from the normal to the refracted ray
What is the relationship between the angle of incidence and the angle of refraction?
As the angle of incidence increases so does the refraction angle
What happens after the angle of refraction has increased so much that it is now along the interface at a right angle to the normal and the angle of incidence increases and what is it called?
If the angle of incidence increases any further, then the incidence ray will only reflect not refract anymore - it is called total internal reflection
What is the critical angle?
The minimum angle at where total internal reflection occurs
How do you investigate refraction?
- Use a ray box with a single slit
- Place glass block on paper and draw outline
- See where light goes after exiting the glass and draw crosses on rays
- Take block away and join crosses and lines before and after it enters the block
- Measure angles of incidence and refraction
- Repeat experiments at different angles
What is diffuse reflection?
When a light ray is reflected on a rough surface so the light is scattered in all directions
What is specular reflection?
When light is reflected on a smooth surface so it reflects evenly
Give examples of a source of white light?
the sun or lightbulbs
What is white light made up of
A mixture of different colours and can be split up into colours using the visible spectrum using a prism
What happens when white light hits a coloured surface?
Some colours that make it up are reflected and some are absorbed
How does an object become a certain colour?
It absorbs the other colours and reflects the colour it is
What does a filter do?
They are pieces of transparent material that absorb some of the colours in white light (e.g blue filters transmit blue light but absorb all the other colours)
What is a lens?
A piece of transparent material shaped to refract light in a certain way
What does the power of a lens describe?
How much it bends light that passes through it - a more powerful lens is more curved and bends the light more
What is a converging lens?
- Fatter in the middle than at the edges
- Makes parallel rays of light converge at the focal point
What is the focal length?
The distance between the focal point and the centre of the lens
What is a diverging lens?
-Thinner in the middle than at the edges
What is the focal point?
The point from which the rays seem to be coming after passing through the lens
What is a real image?
An image that can be projected onto a screen
How can real images only be formed?
By light rays that come together
What is inverted?
Upside down
What forms a virtual image?
An object close to a converging lens
Why is an image called virtual?
Because it cannot be projected onto a screen
What will a diverging lens always produce?
- Virtual images that are the same way up
- Much smaller and closer to the lens than the object
What is the name of the frequencies of light that our eyes can detect?
Visible light
What type of waves are all EM wave?
Transverse waves
Where do all EM waves travel at the same speed?
In a vacuum
What do all objects emit energy by?
Infrared radiation
What is the order of EM radiation in order of ascending frequency?
Radio waves, microwaves, infrared, UV, X-rays and gamma rays
What type of radiation has the longest wavelength?
Radio waves (red)
What do most telescopes use to focus the EM radiation onto a central sensor?
Curved mirrors
What can visible light be used for?
Light bulbs
What can infrared radiation be used for?
Communication at short ranges like computers in the same root or a TV to a remote control unit
What can microwaves be used for?
Communication and satellite transmissions, including mobile phone signals
What are radio waves used for?
Transmitting radio broadcasts and TV programmes
How are radio waves transmitted?
- The radio waves are produced by oscillations in electrical circuits
- Metal rod/wire can be used as an aerial to receive the radio waves
- The radio waves are absorbed by the metal and cause oscillations in electric circuits connected to the aerial
What are oscillations?
Variations in current and voltage
What is refraction?
The bending of the path of a wave due to a change in velocity
What layer in the atmosphere can cause the refraction of some frequencies of radio waves?
The ioniosphere
Are microwaves refracted in the Earth’s atompshere?
No
Can radio waves be refracted in the Earth’s atmosphere?
Yes
When does the intensity of radiation emitted by an object increase?
As its temperature increases
What is the correlation between temperature and wavelength?
The higher the temperature, the shorter the wavelength
What is the power of energy?
The amount of energy transferred in a certain time
How does a system stay at a constant temperature?
It must absorb the same amount of power as it radiates
Describe the Earth’s energy balance
- Earth’s surface absorbs about 1/2 of radiation that reaches it from the Sun
- Re-radiates this energy as IR radiation, which can warm up the atmosphere
- For the temp of the Earth to stay the same, it must radiate energy into space at the same average rate it is absorbed
What is the greenhouse effect?
Gases in our atmosphere that naturally absorb some energy, keeping the Earth at a higher temperature than if there were no atmosphere
What would happen if some greenhouse gases were removed from the atmosphere?
The atmosphere would be able to hold less energy and its temperature would decrease
What can UV radiation be used for?
To disinfect water by killing microorganisms in it
What is fluorescence?
Materials that absorb UV radiation and re-emit it as visible light
What are fluorescent materials often used for?
Security markings, where the materials are only visible when UV light shines on them
What are X-rays used for?
In medicine to make images of inside of the body, as they can pass through muscles and fat easily but bone absorbs some X-rays
What are gamma rays used for?
To sterilise food and surgical instruments by killing potentially harmful microorganisms (as they transfer a lot of energy and can kills cells)
How can gamma rays be used to detect cancer?
- A chemcial that emits gamma rays is injected into the blood
- The chemical is designed to collect inside cancer cells
- A scanner outside the body then locates the cancer by finding the source of the gamma rays
- Gamma rays can pass through all materials in the body
Which type of frequency of waves are more potentially dangerous?
Higher frequency waves, as they transfer more energy
How can too much exposure lead to skin cancer?
Sunlight contains high frequency UV radiation, which is transferred to our cells and can cause sunburn and damage DNA, causing a mutation (cancer)
What can excessive exposure to X-rays or gamma rays cause?
Mutations in DNA that can kill cells or cause cancer
What is EM radiation produced by?
Changes in the electrons or nuclei in atoms
What can radiation cause?
Changes in atoms, such as causing atoms to lose electrons to become ions
