Section12.2 & 13.2

SC Standards Covered Standard PS-7.5Summarize the characteristics of the electromagnetic spectrum (including range of wavelengths, frequency, energy, and propagation without a medium). Standard PS-7.7Explain the Doppler effect conceptually in terms of the frequency of the waves and the pitch of the sound.

The Electromagnetic Spectrum Electromagnetic waves – electric and magnetic waves released by a vibrating electric charge Do not need a medium to travel through All travel at 300, 000, 000 m/s

Electromagnetic Spectrum Electromagnetic spectrum – the entire range of frequencies of electromagnetic waves Low energyHigh energy Long wavelengthShort wavelength Low frequencyHigh frequency

Radio Waves Waves with a wavelength greater than 1m Uses: –Radio signals –MRI –Studying objects in space

Microwaves Waves with a wavelength from 1 m to 1 mm Uses: – cellular telephones –Satellite signals –Heating / cooking food –RADAR –Doppler Radar

The Doppler Effect Doppler Effect – the change in frequency, pitch, due to a moving wave source

Using the Doppler Effect Radar –Shoot radar waves towards a moving object and based on how the wavelengths are shifted, the velocity of the moving object can be determined

–When an object is moving towards you the waves are compressed together, lowering the wavelength, increasing the frequency, which raises the pitch –Click here to see animationClick here to see animation

–When an object is moving away from you, the waves are spread apart more, raising the wavelength, decreasing the frequency, which lowers the pitch –Click here to see animationClick here to see animation

Infrared Waves Waves with a wavelength between 1mm and 400 billionths of a meter –Feels like heat –Uses: Remote controls CD-ROMS Infrared photography Keep objects warm

Visible Light Waves with wavelengths from 400 billionths of a meter to 750 billionths of a meter –Uses Waves that we use to see

Ultraviolet Waves Waves with wavelengths of 750 billionths to 10 billionths of a meter Enters into skin cells –Uses: Causes our skin to make vitamin D To kill bacteria Causes some objects to fluoresce To tan

X-Rays & Gamma Rays Smallest wavelength electromagnetic waves Travel through matter breaking molecular bonds Uses: –X-ray imaging –Radiation therapy –Check for defects and cracks in metallic objects