Edexcel IGCSE Physics 复习笔记 3.1.6 Applications of EM Waves

• Electromagnetic waves have a variety of uses and applications
• The main ones are summarised in the table below:

Applications of EM Waves Table

• A summary of the uses and dangers of different EM waves are summarised in the diagram below:

Uses and dangers of the electromagnetic spectrum

Radio Waves & Microwaves

• These two parts of the spectrum share a lot of similarities and uses
  • Their main uses concern wireless communication – in fact many things that people often assume use radio waves actually use microwaves (e.g. WiFi, radar, mobile phones, satellite communications…)

   

• At very high intensities microwaves can also be used to heat things
  • This is what happens in a microwave oven

   

Infrared

• Infrared is emitted by warm objects and can be detected using special cameras (thermal imaging cameras). These can be used in industry, in research and also in medicine
• Many security cameras are capable of seeing slightly into the infrared part of the spectrum and this can be used to allow them to see in the dark: Infrared lights are used to illuminate an area without being seen, which is then detected using the camera
• Remote controls also have small infrared LEDs that can send invisible signals to an infrared receiver on a device such as a TV
• Infrared travels down fibre optic cables more efficiently than visible light, and so most fibre optic communication systems use infrared

Visible

• Visible light is the only part of the electromagnetic spectrum that the human eye can see
• The human eye can detect wavelengths from 750 nanometres (red light) up to 380 nanometres (violet light)

Ultraviolet

• Ultraviolet is responsible for giving you a sun tan, which is your body’s way of protecting itself against the ultraviolet
• When certain substances are exposed to ultraviolet, they absorb it and re-emit it as visible light (making them glow)
  • This process is known as fluorescence. Fluorescence can be used to secretly mark things using special ink – in fact most bank notes have invisible fluorescent markings on them

   

• Fluorescent light bulbs also use this principle to emit visible light

X-rays

• The most obvious use of x-rays is in medicine
• X-rays are able to pass through most body tissues, but are absorbed by the denser parts of the body, such as bones
  • When exposed to x-rays the bones can a shadow which can be seen using a special x-ray detector or using photographic film

   

Gamma Rays