ELECTROMAGNETIC WAVES

• Electromagnetic waves: a wave that can travel through empty space and through matter.
• EM waves are transverse oscillating waves composed of electric and magnetic fields
• Electromagnetic waves are formed by changing electric field and magnetic field
• speed = $3 x 10^8 m/s$
• EM waves can travel even without a medium (i.e., a vacuum)
• Different type of EM wave:
• Different types of EM waves according to its spectrum:

  1. Radio Waves
  2. Microwave
  3. Infrared
  4. Visible Light
  5. Ultraviolet
  6. X-Ray
  7. Gamma Ray
• Wavelength - the distance between one point on a wave to the nearest point
• Frequency - the number of wavelengths that pass by a point in a certain period of time
• Long wavelength = Low frequency
• short wavelength = high frequency
• What is the relationship between wavelength and frequency?

  Inversely proportional
• High frequency =High energy
• Low frequency = Low energy
• Radio waves are the region in the EM spectrum with the longest wavelength and the lowest frequencies in the EM spectrum. They have wavelengths ranging from 1 cm to 1 km, with frequencies ranging from 30 gigahertz (GHz) to 300 kilohertz (kHz).
• Different bands of Radio waves:

  • Extremely Low frequency
  • Very Low frequency
  • Low frequency
  • Medium frequency
  • High Frequency
  • Very High Frequency
  • Ultra-High Frequency
• Broadcasting - it is the use of electromagnetic waves to send information in all direction
• Carrier wave - an electromagnetic wave that a radio or television station uses to carry its sound or image signals
• Amplitude Modulation - a change in the amplitude of a carrier wave
• Frequency Modulation - change in the frequency in the carrier wave. It also changed the quality of the sound or image
• Microwaves have frequencies higher than those of radio waves. their frequencies range from 300 MHz to 300 GHz.
• Different sub-bands of microwaves:

  • L
  • S
  • C
  • X
  • K
• Uses of microwaves are

  • GPS
  • Active remote sensing
  • Radio detection and ranging ( RADAR)
  • Bluetooth and Wifi Connection
• Infrared (IR) waves are found between microwaves and visible light. They have frequencies ranging from 3 × 10^11 to 4 × 10^14 Hz.
• Different bands of Infrared:

  • Near
  • Mid-
  • Far
• In 1800, William Herschel first recorded the thermal measurement at the far end of the red spectrum, hence the name infrared
• The only part of the EM spectrum that can be seen by the unaided eye is the visible light.
• Visible light has frequencies ranging from 400 to 700 nm
• Different bands of visble light:

  • red
  • orange
  • yellow
  • green
  • blue
  • indigo
  • violet.
• 1801, John Ritter successfully proved the existence of energy beyond the violet spectra of the visible light, naming it ultraviolet
• UV radiation extends from the violet spectra of the visible light through X-rays. It has a wavelength ranging from 10 to 400 nm.
• Bands of Ultraviolet:

  • UVA
  • UVB
  • UVC
• UVA is the least harmful of the three forms of UV radiation.
• UVC is the most harmful
• UVB radiation can cause sunburn because, unlike IR, it causes a chemical reaction on the human skin.
• X-rays were first observed and documented by Wilhelm Conrad Roentgen in 1895.
• X-rays carry 100 eV to 200 keV of energy.
• X-rays can be classified as soft X-rays and hard X-rays
• Soft X-rays carry smaller amounts of energy. This energy allows them to penetrate through matter.
• Gamma rays contain the highest energy of all, possessing a range from 200 keV to about 200 MeV.