Radio Waves
radio ⇒ sound is transmitted through air to radio set via radio waves
information in radio waves can be transmitted by 2 methods.
- amplitude modulation (AM) → as information is conveyed by varying wave amplitude
- Frequency modulation (FM) → information is conveyed by varying the frequency
Radio waves in 3 to 30MHz range ⇒ can be reflected repeatedly off ionosphere (part of earths upper atmosphere) and ground ⇒ to reach places thousands of Km away → useful for long distance communication
stars, galaxies and other celestial objects ⇒ produce electromagnetic waves of wide range of frequencies. sun produces mainly visible light, ultraviolet and infrared. → knowledge about frequencies and intensities ⇒ allow astronomers to deduce the materials, temps, and processes in celestial objects.
Radio waves produced by some stars, quasars, and galaxies ⇒ detected with radio telescopes.
RFID tag ⇒ small and thin circuit ⇒ contains identification data. reader device sends radio wave to tag ⇒ it receives energy. Energy allows tag to transmit data by radio waves back to reader. used in library books, pets, items in warehouses and merchandise in shops
Microwaves
→ in microwave ovens. Wi-Fi signals ⇒ also fall under microwaves.
→ used very extensively for communication. best known example ⇒ mobile phone communication where many transmitters and receivers relay information across whole network
Other uses ⇒ GPS, satellite communication, and radar. Microwaves can also be used for cancer treatment
Infrared
→ skin has thermoreceptors that are sensitive to infrared waves
- thus we feel warm > whe new stand near hot object or fire
Electrically heated rods in ovens ⇒ give out infrared waves or radiation to cook food.
Infrared waves can also be used for data transfer between devices like mobile phones and laptops. ⇒ since higher frequency waves carry more data, infrared can transfer data faster than microwaves. ⇒ infrared waves are used in long distance fiber optic cables for high speed data transfer.
Other common uses of infrared ⇒ in remote controls, camera auto focusing and thermometers that measure body temperature by sensing emitted infrared radiation to produce thermal image. → these thermometers can also be enhanced to detect potential intruders at protected premises and sound alarms. Cold places ⇒ greenhouses made of glass are used to trap long wavelength infrared to maintain a warm interior for plants to grow
Visible Light
Taking photograph on mobile phones ⇒ requires visible light. Visible light can also be used to transfer data directly through air. During surgeries ⇒ optical fibers are very useful for transmitting light to illuminate internal organs
there is research ongoing about role of differently colored light in leaf growth, flowering and root formation
⇒ help farmers to effectively control factors for ideal crop production using artificial light sources instead of relying on natural but unpredictable weather conditions.
→ could be crucial for feeding growing world population
soft material used by dentist to fill up treated tooth cavity ⇒ needs to be cured with light so it can be hardened.
→ chemical process is called polymerization ⇒ where small molecular units called monomers link up to form long chain.
over the years ⇒ different light sources ⇒ have been used to trigger the process.
currently → blue light from LED is used
Photographic film. → has been largely replaced by electronic sensors in digital cameras. Film is coated with chemicals ⇒ that react to visible light of different frequencies. → this allows film to record an image formed by a lens. ⇒ this films respond to UV, X-rays and gamma rays too.
Ultraviolet
UV light ⇒ can be seen by some insects and animals thus giving them a keener sense of sight.
SG ⇒ water treatment plants ⇒ important role⇒ in disinfection and sterilization as it can kill bacteria and viruses.
exposure to suitable dose of UV light ⇒ from sun ⇒ enables our body to produce vitamin D that is good for our bones, muscle’s and immune system. In places ⇒ when there is little sunlight ⇒ people use sun tanning beds to get more tanned skin tone
However ⇒ users have to excersise caution and follow usage guidelines, as over exposure can have harmful effects ⇒ skin cancer and premature ageing
Pigments that glow under UV light ⇒ commonly used in anti forgery features of printed notes.
X-Rays
intensities of X-rays ⇒ passing through different tissue types varies. Parts of body ⇒ that absorb more X-rays ⇒ appear brighter on the image. Thus ⇒ different shades can reveal internal structures such as fractures and cancerous growth in the body.
More advanced medical imaging technique ⇒ is called computed tomography (CT). Rotating X-ray scanner ⇒collects data over a thin slice of patients body ⇒ before moving on to do the same for the next adjacent slice. Data for each slice ⇒ processed by a computer to reconstruct the different types of tissue in that slice. → finally all the slices are combined to form 3D image of scanned volume.
Energetic X-rays ⇒ are also useful ⇒ for killing cancer cells in radiotherapy. → high penetrative power makes it a useful tool to scan for manufacturing defects in metal parts and at airports to scan luggage for prohibited items.
Gamma Rays
Gamma rays ⇒ most energetic waves in the electromagnetic spectrum ⇒ making them very effective for killing germs in food and sterilizing medical equipment
like X-Rays, gamma rays ⇒ can be used for radiotherapy and detecting defects in manufacturing, including in metal objects. However > Gamma rays are usually from a compact radioactive material ⇒ while X-ray machine tends to be bulky and require electrical power
Gamma rays ⇒ have been used to treat cancer, in a procedure known was Gamma knife radio surgery. ⇒ Gamma rays are directed at brain tumors to kill cancer cells.
- hundred of radioactive gamma ray sources are positioned around a special helmet
- emitted gamma rays ⇒ are aimed at a single target such as a tumor
- individual beam from each source is not intense enough to kill cells along its path
- However > when all the beams converge at the tumor ⇒ high intensity of the ray is able to kill cancer cells in tumor