Electromagnetic Wave

Key Stage 4

Meaning

An electromagnetic wave is a transverse wave which transfers energy by oscillating electrostatic and magnetic fields.

About Electromagnetic Waves

Electromagnetic waves are transverse because the oscillation of electrostatic and magnetic fields is perpendicular to the direction of energy transfer.

Electromagnetic waves, like all waves, carry energy and information but they do not transfer mass from one location to another.

All electromagntic waves travel at 300,000,000m/s through a vacuum.

The properties of electromagntic waves depend on their frequency and wavelength. The lowest frequency transmits the least energy so they are the least dangerous. The highest frequency transmits the most energy so they are the most dangerous.

The electromagntic waves you should know in order from lowest frequency (longest wavelength) to highest frequency (shortest wavelength) are:

• Radiowaves
• Microwaves
• Infrared
• Visible Light
• Ultraviolet
• X-rays
• Gamma-rays

Properties

NB: You do not need to remember the exact frequency or wavelength but you should remember which are highest and lowest and put them in correct order.

Electromagntic Wave	Average Frequency	Average Wavelength	Affect on matter
Radiowaves	104Hz	103m	Cause alternating currents in metals. Passes through many non-metals unaffected.
Microwaves	108Hz	10-2m	Cause alternating currents in metals and cause water molecules to oscillate, heating the water.
Infrared	1012Hz	10-5m	Causes atoms and molecules to vibrate, heating the material.
Visible Light	1013Hz	10-6m	Different frequencies are reflected or absorbed by different surfaces giving them colour.
Ultraviolet	1016Hz	10-8m	Can cause electrons in some materials to gain enough energy to leave atoms creating ions which can destroy chemical bonds.
X-rays	1018Hz	10-10m	Can cause electrons in many materials to gain enough energy to leave atoms creating ions which can destroy chemical bonds. However, it often passes through many non-metals without colliding with any atoms.
Gamma rays	1020Hz	10-12m	Causes electrons all materials to gain enough energy to leave atoms creating ions which can destroy chemical bonds. However, it often passes through many non-metals without colliding with any atoms.