Unit 5 - Light And The Electomagnetic Spectrum Flashcards
What is a ray diagram?
A diagram that shows what happens when light is reflected or refracted.
What is the normal?
A line drawn at a right angle to the barrier
What is the incident ray and the reflected ray measured from?
The normal
What waves can be used to also see what happens to light
Water waves as they work the same way when they hit a barrier
What is the law of refraction.
The angle of refraction is equal to the angle of incidence.
What is refraction
When a ray of light moves into a material where it travels at a different speed as it is of a different density
What is the interface
The boundary that a light ray meets when it refracts
Why might there be no refraction
If the light meets the interface at a right angle
What is total internal reflection
When the light is completely reflected inside the glass
What is the critical angle
The angle when the reflected light passes along the interface of the glass block
What shape is the glass block need to be in order for total internal reflection to happen
Semi circular glass block
In a semi circular glass block, what happens if the angle of incidence is less than the critical angle
The small amount of light is reflected most is refracted
What happens if the angle of incidence in a semi circular glass broke is greater than the critical angle
All of the light is completely reflected inside the block
Explain the core practical – investigating refraction
Put a piece of paper on my desk and set a power supply, ray box with a single slit. Put a rectangular glass block on the paper and draw around it. Shine a ray of light onto the block and marks small crosses where the rays go. Take off the block and join the crosses using a ruler to show the path. Join the points from where it entered and left the plot to show the path of inside the block. Measure the angles of incidence and refraction using a normal. If it is at a right angle, nothing will happen. Repeat with different angles.
What is different between seeing luminous and nonluminous objects
With luminous objects, the light from them enters your eye. With nonluminous object, the reflected light enters your eye
What is diffuse reflection
When the light is scattered directions from a rough surface
What is specular reflection
When light is reflected evenly from a very smooth surface such as mirrors
What is white light
Light made up of a mixture of colours that we see as white.
What light comes from the Sun or lamps
White light
What is the visible spectrum
When whites light splits up into different colours using a prism
How do we see coloured objects
Objects of a colour reflects the same colour of this visible spectrum. The rest of the colours are absorbed
How do we see white light
The objects reflects all of the colours
What are filters
Pieces of transparent material that absorb some of the colours white light but transmitting a specific colour.
What is a lens
A piece of transparent material shaped to refract light in a particular way
A more powerful lens means…
The light bends more
What is a converging lens
A lens that is fatter in the middle. This makes parallel rays of light converge at a focal point. The focal point is after the lens
What is the focal length
The distance between the focal point and the centre of the lens
What is a diverging lens
A lens that is thinner in the middle then at the edges and dispersers parallel rays of light. The focal point is in front of the lines as if the dispersed rays of light join at a particular point, it would be in front
What is a real image
An image that can be projected onto a screen and can only be formed by light rays that come together
How is a real image formed
The object must be further away from the lens than the focal point. When the light rays are refracted using the converging lens a real image is formed. This can be projected onto a screen
How is a virtual image formed
The object must be closer to the loans than the focal point. The race that point into the eye after they have been reflected by the lines all point to the focal point where a virtual image is formed. This is formed as if there wasn’t a lens and is the virtual image.
Give an example of a converging lens to form a virtual image
Magnifying glass
What does a virtual image look like
Upright and bigger
What does a real object look like
Upside down and smaller than the object
What do diverging lenses produce
Virtual images that are the same way up, much smaller and closer to the lens than the object
What is visible light
A part of the electromagnetic spectrum that we can see as our eyes can detect a certain frequency
What do you lower frequencies of visible light appears as
More red
What do high frequencies of visible light appear as
More blue
What is ultraviolet
Electromagnetic waves with frequency of the little higher than visible light
What type of wave are electromagnetic waves
Transverse, the electromagnetic vibrations are at right angles to the direction the energy is being transferred
What speed do all electromagnetic waves travel at in a vacuum
3 x 10^8 m/s
What is infrared
Electromagnetic waves with frequency is slightly lower than visible light
What is infrared also known as
Heat
Who was the first person to investigate infrared radiation
William Herschel
What did William Herschel do
He used dark coloured filters on his telescope to help him see the sun safely. He noticed that different colours heated up the telescope different amounts. He wanted to test his idea is that different colours of light contained different amounts of heat so he split sunlight into a spectrum using a prism and put a thermometer in each of the colours and measured the temperature just beyond the red which was infrared
What are the seven colours in the visible light spectrum
Red, orange, yellow, green, blue, Indigo and violet
What electromagnetic waves have a lower frequency than visible light
Infrared, microwaves and radio waves
What electromagnetic waves have a higher frequency than visible light
Ultraviolet, x-rays, gamma rays
What is the electromagnetic spectrum
The full range of electromagnetic waves
How big are the waves if they have a high frequency
Very short
Why do astronomers use different kinds of telescope to study different wavelengths
Different materials affect electromagnetic waves depending on the wavelength
Why do most telescope use curved mirrors
To focus the electromagnetic radiation onto a central sensor
What is visible light used for
Lightbulbs and cameras protect it and record images
Give three uses of infrared
Short range communication such as a TV to its remote control
Grills or toasters
Security systems that have infrared sensors
Give two uses of microwaves
Communication and satellite transmissions including mobile phones.
Microwave oven to heat up food
What are radio waves used for (2)
Transmitting radio broadcasts and TV programmes
Controllers on the ground communicating with spacecraft
What are oscillations
Variations in current and voltage
How are radio waves produced?
By oscillations in electrical circuits
How do aerials work
Aerials are metal rods that absorb radio waves. A transmitting aerial has current moving up and down. These oscillations cause radio waves to spread out from the aerial. The radio waves cause an oscillating current in the receiving aerial.
What layer in the atmosphere can refract some frequencies of radio waves
Ionosphere
What is the ionosphere
Region of charged particles in the atmosphere
Which out of radio waves and microwaves has a greater range
Radio waves
Why might some radio waves be sent back towards the Earth
If they reach the ionosphere at a suitable angle, they may be reflected enough.
Can microwaves be reflected in the earths atmosphere
No
If there is a high temperature, how long will the wavelength be
Shorter
Which part of lavar is the hottest
Yellow
What is the power
The amount of energy transferred in a certain time measured in watts
How can a system stay at a constant temperature
It must absorb the same amount of power as it radiates
How does the Earth re-radiate the energy from the Sun
As infrared radiation
What are greenhouse gases
Gases and all atmosphere that naturally absorb some energy
What is the greenhouse effect
When greenhouse gases absorb the energy keeping the earth at a higher temperature then if there were no atmosphere
Explain the core practical – investigating radiation
Cover for boiling tubes in different coloured materials.
Pour same volume of hot water from a kettle in each tube
Insert a bung with a thermometer into each tune and measure the temperature every 2 minutes for 20 minutes.
Record temperatures
What transfers more energy: visible light or ultraviolet radiation
Ultraviolet radiation
How can ultraviolet be used to disinfect water
If water in plastic bottles are placed in the sunshine for several hours the infrared energy from the Sun will heat the water up enough so that’s the ultraviolet radiation will help to kill microorganisms
What is fluorescence
When materials absorb ultraviolet radiation and re-emit it as visible light
What are fluorescent materials used in
Security markings as they are only visible when ultraviolet light shines on them
Ultraviolet in low energy lightbulbs
These low energy lightbulbs are fluorescent. A gas inside them produces ultraviolet radiation when an electrical current passes through it. A coating inside the glass absorbs the ultraviolet and emits visible light
Why can x-rays be used in medicine to make images of inside the body
X-rays can pass through many materials that visible light cannot however bone absorbs some x-rays which creates the bone image
Apart from medicine what can x-rays also be used for
Airport security to inspect luggage and metal objects
Why my gamma rays be used to sterilise food and surgical instruments
Because they transfer a lot of energy which can kill harmful microorganisms and other cells
What is radiotherapy
The process where gamma rays are used to kill cancer cells
How can gamma rays be used to detect cancer
A chemical that emits gamma rays is injected into the blood which is designed to collect inside cancer cells. A scanner outside the body locate the cancer by finding the source of the gamma rays
Why might microwaves be dangerous to Our bodies
A certain microwave frequency can heat water inside our cells which may cause them to burst
Why are microwaves use in mobile phones not dangerous
They use a different frequency that are not a health risk
What is a danger of infrared radiation
It can damage or destroy cells causing burns to the skin
Give 5 dangers of ultraviolet radiation
It can cause sunburn, damage the DNA, skin cancer, cataracts and damage to our eyes (skiers and mountain is cancer for temporary snow blindness from too much ultraviolet radiation reflected from snow)
Give 2 dangers of x-rays and gamma rays
They can penetrate the body and excessive exposure can cause mutations in the DNA that can kill cells or cause cancer
How is electromagnetic radiation produced
By the changes in the electrons or the nuclei in atoms
Give an example of how infrared and gamma radiation can be produced
When materials are heated the formation of electrons can change which can produce infrared radiation. Changes in the nuclei of atoms can produce gamma radiation
How can the constant temperature of the earth change
When greenhouse gases are added they absorb more energy making the temperature rise. The greenhouse gases can only absorb a certain amount and after that the Earth will return to radiating the same power as they receive
