Transcript Slide 1
Electromagnetic waves are transverse wave, made up of continually changing electic and magnetic fields. Like mechanical waves, electromagnetic waves can travel through most solids, liquids, and gases. They can also travel through a vacuum. TYPES OF ELECTROMAGNETIC RADIATION Radio Waves Micro Waves Infra Red Rays (IR) Visible Light Ultraviolet Rays (UV) X-Rays Gamma Rays the wavelength ( λ ) of electromagnetic spectrum the electromagnetic spectrum in term of Hertz (Hz) temperature of bodies emitting the wavelength (K) PROPERTIES OF ELECTROMAGNETIC RADIATION 1. Travel through vacuum at 300 000 km/s ( 299 792.458 m/s) 2. Exhibit interference, diffraction, and polarization 3. Obey the wave equation; v = f. λ 4. Carry energy from one place to another and can be absorbed by matter to cause heating and other effects RADIO WAVES 1. Long, Medium, & Short Waves ( λ = 2000 – 10 m) - Diffract round obstacle - Reflected by ionosphere 2. VHF and UHF ( λ = 10 m – 10 cm) - Local Radio & TV 3. Micro wave ( λ = few cm) INFRA RED (IR) Anything which is hot but not glowing emits IR < 500 ⁰C emits IR alone ≈ 500 ⁰C emits IR + red light ≈ 1500 ⁰C emits IR + white light Applications: -Pictures to be taken in the dark -Sensors on satellites and aircraft -Dry the paint -Remote Control VISIBLE LIGHT There is a narrow section of the EM spectrum that human can see. It’s called visible light spectrum The frequency of a light wave is related to its color. The amplitude of a light wave is related to its intensity. Brightness is the relative intensity as perceived by the average human eye. Primary Colors of Light Green Secondary Colors Cyan Yellow Blue Magenta Red Complementary Colors Colors that made from addition of secondary color and primary (opposite each other in the diagram above) Monochromatic light can be described by only one frequency. LASER (Light Amplification by Stimulated Emission of Radiation) light is very nearly monochromatic. Polychromatic light is composed of multiple frequencies. Every light source is essentially polychromatic. White light is very polychromatic. Light is produced by one of two methods. 1. Incandescence is the emission of light from hot matter (T ≳ 800 K or 500 C). 2. Luminescence is the emission of light when bound electrons fall to lower energy levels. luminescent incandescent ULTRAVIOLET (UV) RADIATION Ultraviolet (UV) rays have shorter wavelength than light, but can penetrate deeper than light. UV rays from the sun cause the skin to increase its production of a brown chemical called melanin. UV lamp used for scientific or medical purpose or to verify ‘invisible’ signatures on bank documents X-RAYs X-rays can travel through soft substances but not hard, dense ones. They travel through soft tissue, but not hard bone. X-rays are used in hospital to make shadow pictures of parts of the body. X-rays are used at airport to check what may be hidden in the luggage. Gamma Rays Gama rays are shot, high frequency waves. They are type of radioactive decay. Gamma Rays are ionizing radiation and are thus biologically hazardous They can kill living cells and used to sterilize medical equipment by destroying any germs on them end of slide show !! To be continued . . .