Electromagnetic Spectrum

COMMUNICATION

• Long wave radio (1-10km)

- Can be receieved halfway around the world due to diffraction

- They bend around the surfaces of the Earth, and around hills, through tunnels etc.

• TV and FM Radio broadcasting (10cm-10m)

- To get reception, you have to be in direct sight of the transmitter

- Cannot diffract or go around hills; doesn't go far through tunnels

• Short Wave Radio (10-100m)

- Can be receieved from a long distance

- This is due to the waves reflecting off the ionosphere - electrically charged layers in the Earth's upper atmosphere

Satellite Communication

• Shorter wavelengths (1-10cm)
• Use microwaves that pass through the Earth's watery atmosphere without being absorbed

• For a satellite TV, the signal from the transmitter is transmitted to space
• There it is picked up on by a satellite receiver dish orbiting thousands of kilometers above the Earth
• The signal is then transmitted back down to Earth in different directions
• From that it is received from a satellite dish on the ground

Microwave Ovens

• The microwaves are absorbed by the water molecules in the food
• They penetrate a few cm into the food before being absorbed
• The energy is then conducted or convected to other parts of the food

Heating and monitoring temperature

• IR = Heat radiation
• ALL objects give off IR - The hotter the object, the more IR it gives off

Detection

• It can be detected in the dark using night-vision equipment
• This equipment turns it into electrical signals which is displayed on screen as a picture
• Allows things that would be otherwise hidden in the dark, e.g. criminals, to be seen

Dangers

•  Internal heating of body tissue

Communication using optical fibres

• Optical fibres carry data over long distances as pulses of light
• Pulses of light enter a narrow core at an angle
• They are reflected over and over against the sides of the core until they reach the other side
• Used for telephone and broadband internet cables, medical purposes (allows you to "see inside" a body without having to operate), etc.

Photography

• Lens - Focus visible light onto light-sensitive film or electronic sensores
• Apeture - Controls how much light enters the camera (like the pupil of an eye)
• Shutter speed - Determines how long the film or sensor is exposed to the light

Fluorescent Lamps

• UV radiation is absorbed and visible light is emitted
• Nearly all of the UV radiation is absorbed by a phosphor coating on the inside of the glass which emits visible light instead. So it is safe to use
• Fluorescent lights are more energy efficient than filament light bulbs

Dangers

• Skin burns/skin cancer
• Blindness
• Damage to surface cells
• Cell mutations which could lead to cancer

Safety Precautions

• Wear sunscreen with UV filters
• Stay out of strong sunlight

• View internal structure of objects (like bodies)
• Helps doctors diagnose broken bones
• Airport security

X-RAY Images

• X-Ray radiation is directed through the body onto a detector plate
• They can easily pass through flesh but not through more dense materials like bones
• This is why the brighter bits of the x-ray images are shown onscreen
• Barium meal - some patients are ordered to drink barium sulphate which allows their intestines to show up clearly on a x-ray image

Dangers

• Cell mutation and cancer

Safety Precautions

• Lead aprons and shields
• Minimum exposure

Sterilise medical equipment

• By killing microbes
• Better than boiling plastic instruments as they will likely become damaged due to the high temperatures

Sterilise food

• By killing microbes
• Keeps food fresher for longer without needing to preserve it through freezing, cooking etc.

Kill cancer cells

Dangers and safety precautions

• Cell mutation and cancer
• Keep in a lead-lined box
• Wear protective gear when near it
• Minimum exposure time