Electromagnetic Spectrum Flashcards
On a ray diagram what is the normal line?
It’s the line drawn at right angles to the barrier or mirror
Where is the incident Ray and reflected Ray measured from?
The normal
What letter represents the angle on incidence?
I
What letter represent the angle of reflection?
R
Go to page 66 and look at Ray diagrams
Yolo
What is the law of reelection?
When waves are reflected, the angle of reflection is equal to the angle of incidence
When does light travel in different speeds?
In different materials, it travels faster in air than it does in water or glass.
When a ray of light moves into a material where it travels at a different speed, it usually changes direction. What is this called?
Refraction
When is there no change in direction?
When light meets the interface (boundary) at right angles (along the normal)
When light passes from water or glass or air with small angles of incidence most of the light passes through the interface but a little is reflected. As the angle of incidence increases, the angle of refraction also increases until the refracted light passes along the interface. If the angle of incidence increases further, the light is completely reflected inside the glass. What is this called?
Total internal reflection and the angle of incidence at which starts to happens is called the critical angle
What is a ray diagram?
It’s a way of modelling what happens when light is reflected or refracted
What happens when a small amount if light goes through a different material?
Some of its reflected but most of its refracted
What happens when the angle of incidence equals the critical angle?
The refracted light passes along the interface (boundary) of the glass block
What happens when the angle of incidence is greater than the critical angle?
The light is completely reflected inside the block
When you swim underwater, you may be able to see reflections on the underside of the water. What are these caused by?
Total internal reflection
How can we investigate refraction?
By measuring the angles between the light rays and the normal. The light ray approaching the interface is called the incident Ray. The angle between this Ray and the normal and the light Ray leaving the interface is called the angle of refraction
When do you see luminous objects?
When light from them enters your eyes. You see non luminous objects because they reflect light
Most materials have rough surfaces if you examine them closely, so the reflected light is scattered in all directions. What is this called?
Diffuse reflection
Very smooth surfaces such as mirrors reflect the light evenly, what is this called?
Specular reflection
What is the light from the sun or lamps called?
White light
What is white light?
White light is a mixture of different colours of light that our eyes see as white
What can white light be split up into using a prism?
The colours of the visible spectrum
What happens when white light hits a coloured surface?
Some of the colours that make it up are absorbed and some are reflected
Theatres use spotlights to produce effects on stage. Spot lamps produce white light but how can they be coloured?
Using filters
What are filters?
They are pieces of transparent material that absorb some if the colours in white light
Why do you see different colours?
Because you have three types of cone cells in the parts of your eyes that detect light (the retina). Each cone detects red, green or blue light which are the primary colours of light (nit the same as the primary colours of paint). If red cones and green comes both detect light, you see the light as yellow. If all three sets of cones Derek t light, you see it as white
Hat is a lens?
A piece of transparent material shaped to refract light in particular ways. The power of a lens describes 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?
It’s the fatter in the middle than at the edges. It makes parallel Ray’s of light converge (come together) at the focal point and the centre of the lens.
What is a diverging lens?
It is thinner in the middle than at the edges. The focal points if the point from which the rats seem to be coming after passing through the the lens, they go apart at the focal point
Go to pg 72 and 73
And look at the diagrams
What. Does the kind of image formed by a covering lens depend on?
Where the object is
What can a converging lens be used for?
To focus Ray’s of light onto a screen , and image that can be projected onto a screen this way is called a real image
When can real images only be formed?
When light rays come together
What will an object close to a converging lens form and why is it called this?
A virtual image. It is called virtual because it cannot be projected onto a screen, the image appears on the same side of the lens as the object, and is upright and magnified. A magnifying glass is a converging lens
What do diverging lenses always produce?
Virtual images that are the same way up, much smaller and closer to the lens than the object
When do we see things?
When light travels from a source and is reflected by an object into our eyes, they light transfers energy from the surge to our eyes
What type of waves is light?
An electromagnetic wave
Our eyes can decree certain frequencies of light, what do we refer to these frequencies as?
Visible light
What do different frequencies cause us to see?
Different colours, lower frequencies of visible light appear more red and higher frequencies appear more blue
What are electromagnetic waves with frequencies a little high than visible light called?
Ultraviolet
What are all electromagnetic waves and what does this mean?
Transverse waves, thus means that the electromagnetic vibrations are at right angles to the direction in which the energy s being transferred by the wave. All electromagnetic waves travel at the same speed (3✖️10 to the power of 8) in a vacuum. Like all other waves electromagnetic waves transfer energy from a source to an observer
What are electromagnetic waves with frequencies slightly lower than visible light are called ………….., all objects emit energy by infrared radiation. The hotter the object the more energy it emits.
Infrared
Who first investigated infrared radiation?
William Hershcel (1738-1822) he put dark coloured filters on his telescope to help him observe the sun safely. He noticed that different coloured filters heated up on his telescope to different extents and he wondered whether the different co,ours of light contained different amounts of heat
How did William here gel test his idea?
He used a prism to split sunlight and then put a tgemometercin each if the colours in turn. He also measured the temperature just beyond the red end if the spectrum, where there was no visible light
How many colours are in the visible light spectrum
7, they are red orange yellow green belle indigo violet
What does the colour of visible light depend on?
It’s frequency, if the frequency of an electromagnetic wave is lower than the red of light, human eyes cannot see it
Which waves have lower frequencies than red light?
Infrared, microwaves, radio waves
What waves have a higher frequency and high wave length than visible light?
Ultraviolet, X-Ray’s, gamma rays
Go to page 76
Look at the diagram
What is visible light?
It’s the part of the electromagnetic spectrum that our eyes detect. Light bulbs are designed to emit visible light, while cameras detect it and record images
What can infrared radiation be used for?
Communication at shirt ranges (computers in the same room) the information snot along optical fibres is sent using infrared radiation heating food up (grills or toasters) it absorbs the radiation and heats up, security systems (they have sensors that detect infrared radiation emitted by intruders
What do thermal images show?
The amount of infrared radiation given off by different objects
What are microwaves used for?
Communications and satellite transmissions, including mobile phone signals. In a microwave oven, microwaves transfer energy to the food, heating it up
What ar radio waves used for?
Transmitting radio broadcasts and tv programmes are well as other communications. Some radio communications are sent via satellites. Controllers on the ground communicate with spacecraft using radio waves
How are radio waves produced?
By oscillations (variations in current voltage) in electrical circles
Go to page 79
And look at the diagram
How does the intensity of radiation emitted by an object increase?
As the temperature increases. The wavelengths of the radiation emitted also changes with temperature
The higher the temperature …… ……….. ….. ………………….
The shorter the wavelength
What is the amount of energy transferred in a certain time?
The power, it’s measured in watts
For a system in constant temperature what do it need to do?
It must absorb the same amount of piper as it radiates
The earths surface absorbs about half of the radiation that it reaches from the sun. It re-radiates this energy as what?
Infrared radiation, which can warm up the atmosphere
For the earths temperature to stay the same what does it need to do?
It must radiate energy into space at the same average rate as it is absorbed
Go to page 80
And look at the diagram
Some gases in our atmosphere naturally absorb some energy, keeping the Earth at a high temperature than if there were no atmosphere. What is this?
The green house effect and these gases are often called greenhouse gasses
Go to page 81
Look and the diagram carefully
Go to page 82
And read about the practical
What is ultraviolet radiation?
It transfers more radiation than visible light. It is absorbed by most of the Same materials that absorb visible light, including our skin. The energy transferred can be used to disinfect water by killing microorganisms
What is fluorescence?
Materials that absorb ultraviolet radiation and re-emit it as visible light , they are often used in security markings, cost they are only visible when ultraviolet light shines on them
What are X-Ray?
X-Rays can pass through many materials that visible light cannot, eg they can pass through muscles and fat easily but bone absorbs some X-rays. This means X-rays can be used in medicine to make images of the inside of the body. X-rays can also be used to examine the insides of metal objects and to inspect luggage in airport sucker it’s scanners
What are gamma rays?
They transfer a lot of energy, and can kill cells. For this reason they are used to sterilise food and surgical instruments by killing potentially harmful microorganisms
How are gamma rays used in radiotherapy?
Used to kill cancer cells, they can also be used to detect cancer. A chemical is designed to collect inside cancer cells. A scanner outside the body locates the cancer by finding the source of the gamma rays. Gamma rays can pass through all the materials in the body
How can microwaves be harmful?
The heating could be dangerous to people because our bodies are mostly water and so the microwaves could heat cells from
How can infrared radiation be harmful?
Our skin absorbs infrared, which we feel as hart. Too much infrared radiation can damage or destroy cells, causing burns to the skin
How can ultraviolet radiation be harmful?
(From the sun) can cause sunburn and damage DNA, too much ultraviolet radiation can lead to skin cancer. It can also damage our eyesight
How can X-rays and gamma rays be harmful?
Excessive exposure to X-rays or gamma rays may cause mutations in DNA that can kill cells or cause cancer
How is electromagnetic radiation produced?
By changes in electrons, or the nuclei in atoms this can produce gamma radiation
What can radiation cause changes in?
Atoms such as causing atoms to lose electrons to become ions
How can visible light be harmful?
Can damage your eyes, apart from this there is no danger
