The Electromagnetic Spectrum

• Electromagnetic waves transfer energy from a source to an absorber.
• All electromagnetic waves travel at the same velocity through air or a vacuum.
• All waves in the electromagnetic spectrum are transverse waves.
• The electromagnetic spectrum is a continuous spectrum.

  The waves are shown in order from longest to shortest wavelength.

  The waves also increase in frequency and energy along the spectrum.
• Humans cannot see all of the waves in the spectrum, they can only see visible light.
• Electromagnetic waves behave differently when they enter different substances.

  They can be absorbed, transmitted, reflected or refracted
• What happens to each wave depends on the wavelength and the wave speed in different materials.
• Another example is microwaves, which areabsorbed by foods but reflected by metals.
• For example, glass transmits visible light but doesn't transmit ultraviolet
• When radio waves are absorbed by aconductor, they create an alternating current in the conductor
• Information can be coded into the wavebefore it is sent.

  This makes radio waves useful for broadcasting information, for example on TVs or radios
• Changes in the nuclei of atoms can mean that electromagnetic waves are generated or absorbed.
• For example, gamma rays come from changes in the nucleus of an atom.
• Ultraviolet waves can burn human skin and cause it to age quicker than normal.
• Ultraviolet also increases the risk of skin cancer.
• X-rays and gamma rays are both ionising radiation that can cause gene mutation and cancer
• Radiation dose is a measure of the risk of harm after exposure to radiation.