EM waves and their uses Flashcards
What are the 2 uses of microwaves?
- Satellite communication 2. Mobile phones
Why are microwaves used for communication to and from satellites, not radio waves?
Microwaves can PASS EASILY through the Earth’s WATERY ATMOSPHERE- Radio waves can’t
Describe the journey of TV signal from a transmitter to a satellite dish. (for satellite TV) (4)
- The signal from a transmitter is transmitted into space 2. It’s picked up by the satellite’s RECEIVER DISH 3. The satellite TRANSMITS the signal back to Earth in a DIFFERENT direction 4. It’s received by SATELLITE DISH on the ground
Give a bit more detail on the satellites used for receiving and transmitting signals for TV
They orbit thousands of kilometres above the Earth
Mobile phone calls travel as _______ between your phone and the nearest _______
Mobile phone calls travel as MICROWAVES between your phone and the nearest TRANSMITTER
Some wavelengths of microwaves are _______ by ______ ______ and __ __ __
Some wavelengths of microwaves are ABSORBED by WATER MOLECULES and HEAT them up
How can microwaves damage your health, and what has this caused people to think?
- Microwaves heat up water, so if it heats up the water in your cells you can start to cook 2. So people think: using your mobile a lot or living near a MAST could damage your health
Is there any conclusive evidence to prove that using your mobile a lot or living near a mast could damage your health?
No, though there also isn’t any to prove that it doesn’t
What kind of satellites use microwaves (excluding communication ones)
REMOTE SENSING satellites
What do remote sensing satellites do? (3)
- Monitor oil spills 2. Track the movement of icebergs 3. Monitor deforestation etc
What is an argument against microwaves used for mobile phones causing health risks?
One study on the effects of mobile phones on looked at over 400,000 people no connection mobile phone use and occurrence and brain tumours
What is an argument FOR microwaves used for mobile phones causing health risks?
Mobile phone use has INCREASED DRAMATICALLY in the last 15 years there may be LONG TERM EFFECTS that we DON’T KNOW about
What are 2 uses of infrared waves?
- Wireless remote controls 2. Optical fibres
How do remote controls work?
By emitting different PATTERNS of infrared waves to send different COMMANDS to an appliance
What can optical fibres do? How quickly?
Optical fibres can carry DATA over LONG DISTANCES Very quickly
What 2 EM waves do optical fibres use?
- Infrared waves
- Visible light
Describe how optical fibres carry their signal. (3 bits)
- The signal is carried as pulses of light or infrared radiation
- It is reflected off the sides of a very narrow core
- from one end of the fibre to the other
What is visible light commonly used for? (2)
- Optical fibres
- Photography
What do cameras use to focus visible light?
A lens
What does a camera’s lens focus visible light onto? (2)
- A light-sensitive film
- Electronic sensor
What does the lens aperture control?
How much light enters the camera
What is the eye’s equivilant of the ‘lens’?
The ‘pupil’
What does the shutter speed determine?
How long the film or sensor is exposed to the light
What are the 3 things photographers can vary to capture as much or as little light they want in their photograph?
- Aperture
- Shutter speed
- Sensitivity (of the film or the sensor)
What is the name of how pulses of light or infrared radiation are reflected through an optical fibre?
Total internal reflection
(NOT ‘refraction’)
