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.

Electromagnetic waves can pass through any transparent medium.

Electromagnetic waves do not need matter to be transmitted and can travel through a vacuum.

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:


Electromagnetic waves, are transverse with the vibration at right angles to the motion of the wave.

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.

Applications

Electromagnetic Wave	Applications
Radiowaves	Communication, radio broadcasts, television broadcasts.
Microwaves	Communication, cooking food.
Infrared	Remote controls, night vision, thermal imaging, cooking food.
Visible Light	Sight, photography, microscopy, telescopy.
Ultraviolet	Revealing fluorescent ink to detect forged bank notes, tanning beds.
X-rays	Medical imaging of bones. Medical imaging of intestines, using Barium Sulphate, CAT scans to identify tumors.
Gamma-rays	Sterilising food, sterilising medical equipment. Irradiating cancerous tumors.

Dangers

Electromagnetic Wave	Dangers
Radiowaves	No dangers.
Microwaves	May cause internal heating.
Infrared	Can cause skin burns.
Visible Light	No dangers.
Ultraviolet	Can cause sunburn and skin cancer by ionising and damaging DNA molecules leading to a mutation.
X-rays	Can cause cancer anywhere in the body by ionising and damaging DNA molecules leading to a mutation.
Gamma-rays	Can cause cancer anywhere in the body by ionising and damaging DNA molecules leading to a mutation. Can cause radiation poisoning with high exposure.