P13 Flashcards
What are EM waves?
All EM waves are transverse waves that transfer energy from a source to an absorber
All EM waves travel at the same …….
Speed through air or a vacuum
Why can radio waves be hazardous?
Because they penetrate peoples body’s and can heat the internal parts of the body.
Where do radio wave frequency’s range from?
They range from about 300,000Hz to 3000million Hz
How can you produce radiowaves?
You can produce radiowaves by using an alternating current in an electrical circuit. The object ( in which charges the electrons and oscillates to create radio waves ) is called a transmitter.
What happens when transmitted radio waves reach a reciever?
The radio waves are absorbed and then the energy carried by the waves is transferred to the electrons in the material of the receiver. Then this energy causes the electrons to oscillate.
What are radio waves?
Radio waves are EM radiation with wavelengths longer than about 10 cm.
Why can long-wave radio waves be transmitted from e.g. London and recieved halfway around the world?
That’s because long wavelengths diffract (bend) around the curved surface of the Earth.
Why can short-wave radio signals, like long-wave, be received at long distances from the transmitter?
That’s because they are reflected from the ionosphere - an electrically charged layer in the Earth’s upper atmosphere.
What are radiowaves usually used for?
Communication
Give an example of a short-wave radio use?
Bluetooth uses short-wave radio to connect devices without cables
Communication to and from satellites uses…..
Micro waves
How do microwave ovens work?
The microwaves penetrate up to a few centimetres into the food before being absorbed and
transferring the energy they are carrying to the water molecules in the food, causing the water to heat up.
How can infrared radiation be used?
It can be used to monitor/increase temperatures
Light from ordinary lamps and from the sun is called…
White light
The hotter an object is the more …..
Infrared radiation it emits
What are fibre optic cables?
Optical fibres are thin glass or plastic fibres that can carry data (e.g. from telephones or computers) over long distances as pulses of visible light.
How do fibre optic cables work?
They work because of reflection. The light rays are bounced back and forth until they reach the end of the fibre. ( they bounce on a glass fibre )
What is Fluorescence?
Fluorescence is a property of certain chemicals, where ultra-violet (UV) radiation is absorbed and then visible light is emitted.
What waves does the sun produce?
Ultraviolet radiation (UV) is produced by the Sun, and exposure to it is what gives people a suntan.
Overexposure to UV radiation can be
Dangerous
How do X-rays work?
X-rays pass easily through flesh but not so easily through denser material like bones or metal. So it’s the amount of radiation that’s absorbed (or not absorbed) that gives you an X-ray image.
Low frequency waves like radio waves don’t transfer much energy so they mostly pass through….
Soft tissue without being absorbed
What do UV rays do to your body?
UV radiation damages surface cells, which can lead to sunburn and cause skin to age prematurely.
Some more serious effects are blindness and an increased risk of skin cancer.
What can X-rays and gamma rays do to your body?
X-rays and gamma rays are types of ionising radiation. (They carry enough energy to
knock electrons off of atoms.) This can cause gene mutation or cell destruction, and cancer.
What is radiation dose a measure of?
Radiation dose (measured in sieverts) is a measure of the risk of harm from the body being exposed to radiation.
What does the radiation dose depend on?
-the type of radiation used
-how long the body has been exposed to it
-the energy per second absorbed by the body from the radiation
An object that’s hotter than its surroundings….
Emits more IR radiation than it absorbs as it cools down
An object that’s cooler than its surroundings….
An object that’s cooler than its surroundings absorbs more IR radiation than it emits as it warms up
Objects at a constant temperature….
Objects at a constant temperature emit infrared radiation at the same rate that they are absorbing it.
A black surface is better at absorbing and emmiting radiation than a ………
White one
White light uses
Photography
As you increase frequency in EM waves….
The wavelength decreases
