SCIENTISTS OF EM THEORY:

1. James Clerk Maxwell

   He developed and predicted the EM theory and waves. It is a changing electric field that produces a magnetic field even in the absence of electric currents.

2. Heinrich Hertz

   He applied his theories of Maxwell’s to the production and reception of radio waves. He showed that these signals possessed all of the properties of EM waves.

3. Michael Faraday

   He is the father of induction. He concluded a changing magnetic field produces an electric current and it is called electromagnetic induction.

Faraday’s Law: The changing magnetic and electric fields are perpendicular to each other and to their direction of propagation.

4. Andre-Marie Ampere

   He produced a magnetic attraction and repulsion without the use of any magnets.

5. Hans Christian Oersted

   He accidentally discovered that an electric current can create a magnetic field.

BASIC PRINCIPLES OF EM THEORY

1. Many natural phenomena exhibit wave-like behavior.

2. Light can be described as a wave

3. EM waves travel at 3 x 10^8 m/s

4. EM waves are transverse waves

5. When an oscillating charge accelerates, its electric field changes too.

RADIO AND MICROWAVES IN WIRELESS COMMUNICATION

• Medium and high-frequency waves are used for broadcasting by local radio stations.

• In a radio station, the sound is converted by a microphone into patterns of electric current variations called audio-frequency (AF).

• High-frequency radio waves called radio frequency (RF) carriers can be modulated to match the electronic signal.

1. AMPLITUDE MODULATION (AM)

The amplitude of the radio waves changes to match that of the audio-frequency signal. And can be sent over long distances.

2. FREQUENCY MODULATION (FM)

   It is the frequency of the waves that changes to match that of the signal.

Low Frequency: waves are suitable for communication over long distances.

High Frequency: waves can be reflected by the ione sphere. This enables the waves to be transmitted over a great distance.

3. RADAR - RADIO DETECTION AND RANGING

   Consist of an antenna, transmitter, and receiver.

THE APPLICATION OF INVISIBLE HEAT (INFRARED)

• The longer-wavelength infrared waves produce heat and include radiation emitted by fire, the sun, and other heat-producing objects.

• Below 500 Celsius, an object emits only infrared radiation

• Above 500 Celsius, an object glows and emits both infrared and visible light.

APPLICATION OF VISIBLE LIGHT

• when white light passes through a prism, it is separated into its constituent colors: red, orange, yellow, green, blue, indigo, and violet.

• These colors do not distinctly separate but they continuously change from red to violet.

APPLICATIONS OF ULTRAVIOLET RADIATION

• Ultraviolet UV lamps are used by banks to check the signature on a passbook. The signature is marked on the passbook with fluorescent ink.

• UV radiation is also used in sterilizing water from drinking fountains.

• UV radiation in sunlight produces vitamin D.

APPLICATION OF PENETRATING RADIATION AND NUCLEAR ENERGY

• Radiation is the transmission of energy in the form of waves or particles through space or through a material medium.

• Visible lights, the UV we receive from the sun, etc. are all forms of radiation and are called non-ionizing radiation”

• Radiation is particularly associated with nuclear medicine and the use of nuclear energy, along with x-rays, is “ionizing” radiation.

APPLICATION OF X-RAY (PENETRATING RADIATION)

• X-rays come just after the UV rays, they are shorter wavelength but carries higher energy than UV.

• X-rays were discovered by Wilhelm Conrad Roentgen in 1895.

• Short wavelength x-rays can penetrate even through metals.

APPLICATION OF GAMMA RAYS (NUCLEAR ENERGY)

• Gamma rays lie at the other end of the electromagnetic spectrum.

• Gamma rays are emitted by only the most energetic cosmic objects such as pulsars, neutrons stars, supernovas, and black holes. Terrestrial sources include lighting, nuclear explosions, and radioactive decay.

• Gamma rays can destroy living cells

• Gamma rays are used to treat cancer through the process called radiotherapy.

THE EFFECT OF EM RADIATION ON LIVING THINGS AND THE ENVIRONMENT

1. Ionizing Radiation

   Is a form of energy that acts by removing electrons from atoms and molecules of materials that include air, water, and living tissue. And can travel unseen and pass through these materials.

2. Non-Ionizing Radiation

   Is low-energy radiation that does not have enough energy to remove an electron (negative particles) from an atom or molecule. This radiation exists all around us from many sources.