Electromagnetic spectrum Objectives: 1.Define electromagnetic spectrum 2.Calculate frequency of waves 3.Explain what types of waves used to observe celestial bodies and why

Electromagnetic spectrum Form of energy Does not require a medium to travel Dual nature: – Wave – Particle Waves have troughs and crests Frequency of waves determines properties – Frequency = wavelength/speed – Speed of light 3 X 10 8 meters/second – Units is “hertz”; one cycle per second

Properties of waves Visible light falls near the middle of the electromagnetic spectrum High frequency waves have high energy Low frequency waves have low energy – Energy = (Planck’s constant*speed of light)/wavelength – Waves longer than visible light are not harmful to life (non-ionizing radiation) – Waves shorter than visible light cause damage to DNA and can be harmful or lethal (ionizing radiation)

Ranges of wavelengths

“White” light Light appears differently to us because we have neurons that can detect energy from different wavelengths All colors mixed together form “white light” When light is bent or “refracted”, through a denser medium, shorter wavelengths bend more. – Important for understanding properties of light sources – Also the source of…..

…rainbows!!

Why is it useful to see more wavelengths of light? Gather more information! Different objects in the universe emit differing wavelengths We can determine what elements are emitting those wavelengths – Shows us the compositions of stars – Planets

Different telescopes exist for differing wavelengths

Frequency problem sets (due at the end of class) Radio broadcasts from WVBU produce light waves with frequency 90 MHz ("mega"Hz, or "millions of Hz"). Calculate the wavelength of these waves.