Physics - 13 Electromagnetic Waves - 13.3 Communications & 13.4 Ultraviolet Waves, X-Rays, and Gamma Rays

Carrier wave

waves used to carry any type of signal

How shorter wavelength of carrier wave affects properties [3]:

- more information

- shorter range (due to higher absorption)

- less dispersion

Radio wave transmission [3]:

- long wavelength (LW)

- medium wavelength (AM)

- short wavelength (FM)

Radio wave transmission: long wavelength (LW) [4]

- ground waves

- long range

- follows curvature of Earth and diffracts around objects

- national and international radio stations

Radio wave transmission: medium wavelength (AM) [4]

- sky waves

- limited range

- reflect off ionosphere and Earth's surface

- local radio stations

AM stands for:

Amplitude Modulation

Radio wave transmission: short wavelength (FM) [5]

- space waves

- must be in 'line of sight'; cannot penetrate objects

- can penetrate atmosphere (satellite)

- TV broadcasting

- carry more information

FM stands for:

Frequency Modulation

Microwave transmission

communication to and from satellites as they penetrate the atmosphere

Microwaves penetrate the atmosphere without [4]:

- reflection

- refraction

- diffraction

- absorption

Modulation

to change a signal

Oscillator

device that supplies carrier waves in the form of an alternating current

Transmitter

device that sends out signals in the form of radio waves

Audio signal

alternating current representing a sound wave

Total internal reflection

the complete reflection of light by the inside surface of a medium

Optical fibre communication

- light transmits through glass over long distances with very little absorption

- light reflects off internal surfaces of glass when it bends

Advantages of optical fibres [2]:

- carries more information as visible light and infrared have short wavelengths

- less susceptible to interception

UV waves have a (longer/shorter) wavelength than visible light and carry (more/less) energy

shorter, more

Uses of ultraviolet waves [2]:

- inks that glow under ultraviolet light

- security markers

Dangers of ultraviolet waves [2]:

- harmful to eyes and may cause blindness

- harmful to skin and may age prematurely, cause sunburn or skin cancer

Protection against ultraviolet waves [2]:

- wear sun cream and sunglasses when outside to block UV

- don't go over recommended time in a sun bed

Why are x-rays and gamma rays similar?

they have a similar wavelength

X-rays and gamma rays have a (long/short) wavelength and carry (more/less) energy than the rest of the spectrum

short, more

What stops x-rays and gamma rays?

thick lead plate

X-ray production:

produced in x-ray tubes when fast-moving electrons or other particles strike a metal target

Gamma ray production:

produced when unstable nuclei decay

(Gamma rays/x-rays) have a shorter wavelength

gamma rays

Uses of x-rays [2]:

- detecting internal cracks in metal objects

- creating images of broken bones

Uses of gamma rays [3]:

- irradiation of food

- sterilisation of medical equipment

- chemotherapy (killing cancer cells)

Dangers of x-rays and gamma rays [3]:

- both are ionising, causing atoms to become charged by dislodging electrons

- high doses will kill living cells

- low doses cause cell damage, gene mutation and cancer

Film badge

device that measures the approximate amount of radiation received in a given period