CH 13: Electromagnetic Waves

• The electromagnetic spectrum consists of electromagnetic waves of a continuous range of frequencies.
• Electromagnetic waves are transverse waves that consist of an electric field and a magnetic field which are perpendicular to each other.
• Energy is transferred by electromagnetic waves from one point to another without the need of a medium, for example, the sun and the earth.
• The speed of electromagnetic waves traveling in vacuum is 3 times 10 to the power of 8 meters per second.
• The relationship between the speed of electromagnetic wave v, wavelength lambda and frequency f can be expressed by the following formula v equals to f lambda.
• All electromagnetic waves obey the laws of reflection and the laws of refraction.
• The frequency f of an electromagnetic wave is dependent on its source, wavelength lambda and the speed v of electromagnetic waves depend on the refractive index of the medium where the wave travels.
• Visible light is the only electromagnetic wave that can be seen by human eyes.
• Other electromagnetic waves in the electromagnetic spectrum are invisible to human eye.
• The first level of the electromagnetic spectrum is radio waves, followed by microwaves and infrared, then visible light, then ultraviolet x-rays and gamma rays.
• Gamma rays are radioactive rays coming from nuclear explosions and atomic bombs that can damage healthy cells and cause tissue injuries.
• Overexposure to ionizing radiation can cause premature aging, sterility, cancer, and even death.
• Non-luminous objects reflect certain color lights and absorb the remaining color lights, hence they are seen as a specific color.
• The area with high temperature will be represented in orange color and the area with low temperature will be represented in cold colors like purple and dark blue.
• Visible light is produced by luminous objects such as fire, the sun, the star, and light bulb.
• X-rays are high frequencies and high energy X-rays that can penetrate many materials and damage healthy cells.
• Ionizing radiation is harmful to living cells and the extent of damage to the living cells depends on the type of radiation, the amount of radiation, the duration of exposure, and which particular organs are exposed.
• Exposure to ionizing radiation can damage the genetic material DNA contained in the body's cells, causing genetic mutations and potentially being passed to future generations.
• Visible light is used in data transfer, telecommunication, endoscopy, photography, display in television sets and computer monitors, and camera.
• Electromagnetic waves cause electrons in atoms to gain large amounts of energy and escape from the atoms, making the atoms charged and unstable.
• Ultraviolet rays can kill bacteria and viruses.
• Ultraviolet rays can cause fluorescent effects when some chemicals absorb UV radiation and appear to be glowing.
• Overexposure to ultraviolet rays can cause sunburn and even skin cancer.
• Ultraviolet rays are produced by the human skin when exposed to sunlight and are also used in skin tanning.
• The wavelength traveling from the top to the bottom of the electromagnetic spectrum becomes shorter, meaning the wavelength at the top will be longer and the wavelength at the bottom is shorter.
• For frequency, the frequency at the top of the electromagnetic spectrum is lower while the frequency at the bottom is higher.
• In terms of energy, the energy for the wave at the top of the electromagnetic spectrum is lower and the electromagnetic waves at the bottom are higher.
• Radio waves have lower frequencies and longer wavelengths, are easy to travel in long distance without reflection, consume low energy and hence low cost, and are used to transmit signals and data.
• An antenna is used to transmit and receive the signals in radio waves.
• Microwaves are also used in transmitting data and sickness, are easy to control and direct, and examples of usage are satellite communication and microwave argon remote sensing.
• Microwaves have wavelengths of several mm to several cm, and if the size of raindrops is larger than the wavelength of the microwaves, the waves can be reflected and change direction, hence the receiving antenna cannot receive any signals.
• Infrared is produced by heat, some animals can see infrared lights which help them to detect warm blooded animals, and examples of usage are night vision binoculars and thermal imaging.