# Physics P1.2

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How many EM waves are there?
Seven
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How are the different EM groups separated?
By their wavelengths
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What is special about the spectrum?
The groups merge together forming a continuous spectrum
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What type of waves are the EM waves?
Transverse
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How fast do EM waves travel in a vacuum?
The speed of light. 3X10 m/s
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Which side of the EM spectrum has the shortest wavelength?
The ones with higher frequencies
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Who discovered infrared radiation and when?
Herschel in 18000
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How did he discover infrared radiation?
He knew that white light goes through a prism to create a spectrum of colours. He created the spectrum on a screen. He wanted to measure the heat of every colour and noticed it increased from violet to red. He measured past the red spectrum
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How did he discover infrared radiation? Pt2
and recorded the highest temperature which was infrared.
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Who discovered ultra-violet radiation and when?
Ritter in 1801
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How did he discover ultra-violet radiation?
He knew that silver chloride turned black when exposed to light. He wanted to measure how quickly it turned black in different colours of light. He did it in a dark room and used a prism&timed how long it took to change in each colour. The strips
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How did he discover ultra-violet radiation? Pt2
changed quickest towards the blue end of the spectrum.Just past the violet spectrum he saw the quickest change which was ultra violet radiation.
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In what ways does the frequency of the wave change how it reacts with matter?
It can either be absorbed, reflected, or transmitted.
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What normally happens wit the EM waves at each end of the spectrum?
They pass through material
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What normally happens wit the EM waves in the middle of the spectrum?
They are absorbed
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What does the frequency of the waves determine?
The energy of the waves
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Generally, the higher the frequency...
The more energy the radiation has and the more harmful it is
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How to microwaves heat things?
They have similar frequencies to the vibrations of many molecules so they increase the vibrations which heat them up.
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Why does the fact microwaves can heat things make them dangerous?
They can heat human body cells
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What are microwaves used for? Why are they considered as 'worrying' in this way
Mobile phones. They are held close to the brain and this could link to brain tumours but nothing has been proved.
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How does infrared radiation heat things?
They can make the surface molecules of any substance vibrate which heats it.
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It has a higher frequency than infrared radiation and carries more energy this can cause some skin burns for long exposure.
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How does UV radiation heat things?
it has more energy than infra-red and it is 'ionising' so it knocks electrons of atoms?
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It can cause sunburn when the skin cells absorb the UV rays in sunlight, this can cause cell mutation or destruction which will cause skin cancer and also eye damage
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What makes gamma rays and xrays damaging and penetrating?
They carry a lot of energy and ionising which means they can penetrate further into the body. This can cause cell mutation or destruction which can damage tissue or lead to cancer
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What are radio waves mostly used for?
Communications
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They are used to broadcast TV and radio signals to transmit satellite signals. They have short wavelentghs of around 10cm to 10m s you have to be in direct site of the transmitter and it doesn't work in tunnels or on hills.
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Long-wave radios have a wavelength of 1-10Km and can be sent half way around the world and can get around things like tunnels and hills.
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They have a wavelength of around 10m-100m and can be received at long distances from the transmitter. This is due to them being reflected from the ionosphere. This is the same for medium-wave signals
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What are microwaves mostly used for?
Satellite communications and mobile phones.
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Why is microwaves used for communication?
They can pass easily through the Earths watery atmosphere
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How is microwaves used for satellite TV&Mobile phones?
The transmitter transmits into space and it is received from a satellite dish orbiting the earth and sends it back to Earth in a different direction and a satellite dish on Earth receives it
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What is the negative to microwaves being used for satellite TV?
There is a slight time delay between the the signal being being sent and received.
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How do microwaves work?
The water molecules in food absorb the microwave. They only penetrate a few cm into the food before being absorbed. They energy of the absorption heat it up and it is conducted to the other parts of the food. This microwave is a different frequency
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What can infra-red be used for?
Grills&toasters, Transmit short range information in remote controls, phones and laptops. Security systems by detecting the intruders body heat.
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How is infra-red used in optical fibres?
Data is passed in pulses of IR radiation. (eg telephone wires)They bounce off the sides of the inner core which is usally glass or plastic
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The hotter the object...
The more IR radiation it gives out
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Explain how infra-red can be used to monitor temperature?
Heat loss can be detected by infra-red sensors, night-vision sensors turns it into an electrical signal and it is displayed on a screen. Th hotter something it is the brighter it is.
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How is the night vision equipment used?
Police and the army to find people.
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How do you see?
When light enters your eye it gets refracted through the lens and focused on the retina. The message is sent to the brain which interprets it.
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How does photography work?
The camera lens focuses visible light onto light sensitive film or an electronic sensor that records the image.
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What does the lens's aperture do?
Controls how much light enters the camera
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What does the shutter speed do?
Determine how long the film or sensor is exposed to light
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What is ultraviolet mostly used for?
To detect fake bank notes
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How does fluorescence work?
UV radiation is absorbed and then visible light is emitted.
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How do florescent lamps work?
They use UV radiation to emit light, they are safe to use as the UV radiation is absorbed by a phosphor coating
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How do security pens work?
The ink is only visible in UV light so the police can identify your property.
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How can UV disinfect water?
The radiation kills off any viruses or bacteria in the water
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How is UV helpful with bank notes?
Special markings in florescent ink is on bank notes and under UV light it will display the markings. Fake notes will glow all over as the florescent ink is not in the special markings
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Take X-rays
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How do X-rays work?
They pass easily through flesh but not so easily though metal or bones. So the image features what has or has not absorbed the X-ray.
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What are the drawbacks of X-rays
They can cause cancer so radiographers wear lead aprons and leave the room.
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What else can X-rays be used for?
Airport security use it to scan luggage or evn people but it is lower level X-rays that they use.
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How does gamma radiation kill cancer?
The right amount of dosage of the ray is directed onto cancer cells to kill them. However it makes the patient feel very ill.
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How can gamma rays diagnose cancer?
A radioactive isotope is injected into the patient and a gamma camera detects where the isotope travels which creates an image that can be used to detect where their might be cancer.
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How does gamma rays sterilise food and medical equipment?
If food is exposed to a high dose of it it kills the microbes in it. Medical instuments are also sterilised this way instead of being boiled.
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What are the pros of gamma rays being used to sterilise things?
It doesn't involve high temperatures so they can be sterilised without damage.
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How do gamma, alpha or beta ionise?
They transfer energy. They bash into atoms and knock electrons off of them.
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## Other cards in this set

### Card 2

#### Front

How are the different EM groups separated?

#### Back

By their wavelengths

### Card 3

#### Front

What is special about the spectrum?

### Card 4

#### Front

What type of waves are the EM waves?

### Card 5

#### Front

How fast do EM waves travel in a vacuum?