Electromagnetic Waves

Main Concepts

• Accelerating charges form fluctuating electric and magnetic fields.
• They are transverse waves.
• These fields decrease rapidly from source, but are still detectable at a distance.
• An electromagnetic wave (EM) is created.
• EM waves can travel through a vacuum.
• EM wave speed in a vacuum is 3.0 x 10⁸ meters/sec.
• Have a wide range of wavelengths (up to 10²⁵ Hz !)

Examples

• 1 Hz to 10⁸ Hz - radio waves
• 10⁸ to 10¹⁴ Hz - microwaves
• 10¹¹ to 10¹⁴ Hz - infrared light
• 10¹⁴ to 10¹⁵ Hz - visible light
• 10¹⁵ to 10¹⁷ Hz - ultraviolet
• 10¹⁷ to 10²⁰ Hz - X-rays
• 10²⁰ to 10²² Hz - gamma rays
• 10²² to 10²⁵ Hz - cosmic rays

EM put to Human Use

• 30 to 300 Hz - USN submarine communications.
• 550 kHz to 1.6 MHz - AM radio. MHz = 1 x 10⁶.
• 49 MHz - baby monitor.
• 54 to 72 MHz - TV channels.
• 88.5 MHz to 108 MHz - FM radio.
• 825 to 849 MHz - cell phones.
• 2.5 GHz - microwave ovens. GHz = 1 x 10¹².
• 10 GHz - radar band (one of many).
• 3.4 x 10¹⁴ Hz - TV remote control.
• 4 x 10¹⁴ to 8 x 10¹⁴ - visible light.