The Electromagnetic Spectrum: the family ofLink to the 'Light' index...

At GCSE level, from memory you should be able to list the parts in order of energy (relate how that relates to frequency and wavelength) and know how they are produced, detected and their dangers and uses - a rough idea of their approximate wavelength is also useful at GCSE level (but essential at A level!).

The range of values for wavelength is so vast that you need to know your S.I. prefixes to do calculations using the wave equation relating to the EM Spectrum.

Electromagnetic radiations are disturbances in an electric field.

They travel as waves and move energy from one place to another.

They can all travel through a vacuum and do so at the same speed.

The waves cover a continuous range of wavelengths called the electromagnetic spectrum.

The uses and hazards of the radiations in different parts of the electromagnetic spectrum depend on their wavelength and frequency.

 

  • The Electromagnetic Spectrum is a continuous band of electromagnetic radiation.
  • It is not made up of particles of matter - but rather of photons (a concept not met until A level - but the idea is that light is made up of photons which are little quanta (or packets) of energy)). Electromagnetic radiation is composed of rays of pure energy.
  • All electromagnetic rays have similarities in that they all travel at the same speed in a vacuum - 3.0 x 108 m/s and are all made up of photons.
  • Electromagnetic waves differ in their wavelength, frequency, energy and method of production, but their speed in a vaccuum is always the same.

The parts of the electromagnetic spectrum are arranged in the table below in order of decreasing photon energy, decreasing frequency or increasing wavelength. Each part is named according to its origin and frequency/wavelength range. Light energy is the most familiar part of the spectrum and it is often referred to as the 'family of light'. Some parts of the e.m. spectrum can be directly detected by humans, others cannot. 

 

See the table below:

indicates that the rays are harmful because they are of high enough energy to be ionizing radiation.

 

Type of Electromagnetic Energy

Source of radiation

Detectors

Typical Wavelength

Uses
Dangers

 

Radioactive nuclei

Geiger-Müller tube

10-12 m

  • Radiotherapy
  • Diagnostic work with a gamma camera
  • Pipe leakage

cancer and mutations deep in the body

 

X-ray tubes - produced when high energy electrons hit a metal target.

Also given out from black holes and very bright stars

Photographic film

10-10 m

(size of an atom)

cancer and mutations deep in the body

Ultra Violet (UV)

Very hot objects, sun, sparks, mercury lamps.

Photographic film, skin (it causes sun tans and skin cancer -see ozone layer depletion), makes fluorescent things glow with visible light.

10-8 m

skin cancer and cateracts

Visible Light
Very hot objects - like the Sun or stars, hot metals (filament lamp), fluorescent objects, and visible lasers, LEDs.
Eyes, photographic film, an LDR.

10-7 m

(Red end is about 700nm - Blue end about 400nm)

  • One of our main forms of one to one communication!
  • Warning of dangers and location of food etc.
  • Writing, painting etc.
Very bright light can damage the retina

Warm or Hot objects, sun, IR lasers

Skin, a blackened thermometer, a thermistor.

10-5 m

  • To keep us warm
  • To cook food
  • Remote control devices for TV etc.
High intensity can burn the skin and retina

Microwaves

Here is a link to news stories about possible dangers of microwave radiation

 

A PowerPoint for you...

Short wave radio transmitters (cell phone communications) and microwave ovens (these contain a magnetron - a high-powered vacuum tube that generates coherent microwaves).

.

Aerial with a short wave radio set, or a satellite dish.

Water filled objects (such as food) get very hot

cm

High intensity and/or energy can cause heating effects within tissue - whether other biological effects take place is debatable - some scientist think it may cause tumour growth - but this is not by the route recognized (it is none ionizing)
Radio and TV waves

Radio and TV transmitters

Aerial with a TV set or a radio set.

(they CANNOT be heard!!!!!)

km

  • Communication
None known unless intensity is abnormally high

 

Most parts of the electromagnetic spectrum can be captured by telescopes to give us more information about the Universe.