⭐️Topic SP5 - light and the EM spectrum Flashcards
How can you model wether light is reflected or refracted?
- a ray diagram
- using waves on water
What is the normal?
The line on a ray diagram at right angles to the barrier/mirror
From where do you measure the angles of the incident ray and reflected ray?
From the normal
What is the law of reflection?
Where the angle of reflection is equal to the angle of incidence when waves are reflected
What is refraction?
Where light changes speed upon moving into a different material
When doesn’t light change direction when meeting a different density?
When it enters the material along the normal at right angles to the boundary
What happens to the reflection of light when it travels from water/glass to air with small angles of incidence?
Most of the light passes through the interface and little is reflected
What is total internal reflection?
When the angle of incidence is greater than the critical angle and the light is completely reflected inside the block
When does refracted light pass along the interface of the glass block?
When angle of incidence = angle of refraction.
What are non luminous objects?
Objects that do not reflect light
What is diffuse reflection?
Reflection from objects with a rough surface that cause the light to scatter in all directions.
Give an example of specular reflection
A mirror as light reflects evenly
What colours make up white light?
Red, orange, yellow, green, blue, indigo, violet
What does a prism do to light?
Split it up into a visible spectrum
Why does an object look a specific colour?
Because it absorbs all the colours of the spectrum but reflects the colour it looks
Why do object look white?
As it absorbs all colours
How can light be made coloured?
By transmitting the colour they look and absorbing the rest?
What colours in white light are transmitted and absorbed by red glass?
Red light is transmitted and all the other colours are absorbed
What does the power of a lens describe?
How much it bends light that passes through it
The more powerful a lens…
The more curved it is and the more it bends light
Describe a converging lens
It’s fatter in the middle than at the edges and makes parallel rays of light converge at the focal point
What is the focal length?
Distance between the focal point and the centre of the lens
Describe a diverging lens?
It’s thinner in the middle than at the edges and the rays seem to be coming from the focal point after passing through the lens
What is a real image?
An image that can be projected on a screen
What is needed to form a real image?
A converging lens as it can only be formed by rays that come together
What kind of image do you get you put an object near a converging lens?
A virtual image that looks bigger than the actual object and appears in front of the object
What kind of image do you get when you put an object far from a converging lens?
A real image that appears behind the lens, smaller than the object as upside down
What is a virtual image?
An image that can’t be projected onto a screen
What kind of image do diverging lenses always produce?
Virtual images that are the same way up and much smaller and closer to the lens that the object
What are the frequencies are eyes can detect referred to as?
Visible light
What kind of wave is light?
An electromagnetic wave?
What kind of waves are all em waves?
Transverse (their vibrations are at right angles in which the energy is being transferred by the wave)
What’s significant about the speed of em waves?
They all travel at the same speed of 3x10^8 m/s in a vacuum
What do em waves do?
Transfer energy from the source to the observer
What causes us to see different colours?
Different frequencies
What frequencies appear what colour in visible light?
Lower frequencies appear more red and higher ones appear more blue as reds have the longest wavelengths and blues have the shortest wavelengths
How do you know if an object’s emitting a lot of infrared radiation
It’s very hot
What do all objects emit?
Infrared radiation
Give an example where we can feel the effects of infrared?
When energy from the sun is transferred to our skin
Give two similarities between infrared and UV radiation
They can both be detected by certain animals and they both can’t be detected by humans
What did Herschel discover?
Infrared radiation
How did Herschel make his discovery?
By putting thermometers at each colour of white light and then putting one beyond the red end of the visible light spectrum
Why did Herschel think certain colours of visible light had different ‘amounts of heat’?
As while observing the sun, he found that different coloured filters heated up his telescope to different extents
What is the order of the EM spectrum from lowest frequency to highest frequency
Radio waves, microwaves, infrared radiation, visible light, ultraviolet, x rays, gamma rays
What is the frequency of visible light?
10^-6
Why do scientists need to use different types of telescope to study different wavelengths from space?
As different materials effect em waves depending on the wavelength e.g. all gamma rays are absorbed by the atmosphere
Why do most telescopes use curved mirrors?
To focus EM radiation onto a central sensor. Type of material and size of telescope depends on wavelength of radiation studied
How does the atmosphere effect radio waves?
The ones with the shorter wavelengths aren’t absorbed by the atmosphere but the longer wavelengthed ones are
What part of the em spectrum do our eyes detect?
Visible
How is infared radiation used?
- Short range communication e.g. tv remote
- to heat food as it absorbs the radiation like in a grill/toaster
- security systems with sensors that detect infrared emitted by intruders
How are microwaves used?
- For communication and satellite transmission like phone signals
- to cook food in a microwave as they transfer energy to the food, heating it up
How are radio waves used?
- Communication like Transmission of radio broadcast and tv programs
- satellite communication
How does ground control communicate with spacecraft?
Using radio waves
What are radio waves produced by?
Oscillations in electrical circuits
What direction do waves travel?
Straight line unless reflected or refracted
How are radio waves released and received?
- Current moves up and down a transmitting aerial
- Oscillations cause radio waves to spread out from the aerial
- Radio waves cause an oscillating current in the receiving aerial
How does the ionosphere affect radio waves and microwaves?
It usually refracts radio waves back to earth if they are at a suitable angle and it transmits microwaves
Why is there a maximum range for microwave communication?
As the curve of the earth surface gets in the way
What is the ionosphere?
A region of charged particles in the atmosphere
What’s the difference in terms of communication range between radio waves and microwaves?
Radio waves have a much greater communication distance than microwaves
When does intensity of radiation emitted by an object increase?
As it’s temperature increases
What’s the relationship between wavelengths of radiation and temperature?
The higher the temperature, the shorter the wavelength of radiation
What is power and what is its unit?
The amount of energy transferred in a certain time and is measured in watts (w)
What is needed for a system to stay at a constant temperature?
The system must absorb the same amount of power as it radiates
How does the earth re radiate heat it absorbs from the sun?
as Infrared radiation
What is the greenhouse effect?
Where gases in our atmosphere like carbon dioxide naturally absorb some energy keeping the earth at a higher temp.
What use does uv light have?
- Disinfect water by killing microorganisms
- used in fluorescence in security markings
What is a fluorescent material? I
a materials that absorbs UV radiation and re emits it as visible light
How do low energy light bulbs work as fluorescent lamps?
As a gas inside them produces uv radiation when an electrical current passes through it and a coating on inside the glass absorbs the uv and emits visible light
How are x rays used?
- to take images of inside the body
- to examine inside of metal objects
- to inspect luggage at airport security
Why do medical x rays work?
As they can pass through muscles and fat easily but bone absorbs some x rays hence why they are visible in x ray scans
What are the uses of gamma rays?
- sterilise foods and surgical instruments
- kill cancer cells in radiotherapy
- detect cancer cells
Why are gamma rays useful for sterlising surgical instruments and food, and killing cancer?
As they transfer a lot of energy and can kill cells
How do gamma rays detect cancer cells?
A chemical that emits gamma rays is injected into the blood. It collects inside cancer cells and a scanner locates the scanner by finding the source of gamma rays
Why couldn’t gamma rays produce images of inside the body like x rays?
As gamma rays pass through all materials in the body
Why are phones safe for humans despite they emit microwaves?
As they use specific microwave frequencies that don’t effect our cells
What can too much infrared do to humans?
Damage or destroy cells and cause burns to the skin
Why is UV radiation dangerous?
It can cause sunburnt, damage to DNA and prolonged exposure could lead to skin cancer
How do you protect yourself from the sun?
Where sun cream with high SPF, cover up with closing and hats and stay out of the strongest sunshine
Give an example of the effects of UV radiation to or eyes.
Skiers and mountaineers can suffer temporary ‘snow blindness’ due to UV radiation reflecting from the snow
Why are x rays and gamma rays most dangerous?
As they have the highest frequencies and shortest wavelengths
What are the dangerous of x rays and gamma rays?
They may cause mutations in DNA that can kill cells or cause cancer
