Waves and Sound

Waves and Sound

1. Electromagnetic Waves

   • can travel in a vacuum and at exactly the same speed in a vacuum
   • are transverse waves
   • carry energy.
   • can be reflected and refracted.
   • Gamma Waves: O.O1nm
     • Treatment of tumours, sterilising medical equipment and kill surface bacteria on foods.
     • Can disrupt DNA in cells, and causes cancers.
   • X-Ray Waves: 0.1nm
     • Diagnosis & therapy, body scanning in airports, scanning people for cancer.
     • causes cancers & harmful to cells.
   • Ultraviolet Waves: 10nm
     • Detect forgeries in banknotes & in water chillers to destroy bacteria which otherwise could build and cause disease and contamination.
     • Skin cancers and damage to eyes.
   • Visible rays: 50nm
     • Photosynthesis, vision & photography
   • Infrared: 0.01nm
     • Toasters, ovens & grills. Night vision equipment and security systems for cars.
     • Over exposure can cause damage to cells and sunburn or other skin burns.
   • Microwave: 3cm
     • Mobile and satellite transmissions, microwave oven and navigation for planes and ships (GPS).
     • Microwaves are absorbed by water molecules - this can harm our bodies as we are made up of water - to limit the risk, interlocks are fitted into the ovens to prevent production of microwaves when the door is left open.
   • Radio: 100m
     • Communication: Television and FM Radios (use short wavelengths), and use with pilots, policemen, seafarers and military.
     • Claims to cause cancers & leukaemia etc, not reliably proven.

2. SOUND

   • Sound at frequencies above 20kHz is called Ultrasound.
     • Bell Jar Experiment explains why sound cannot travel through a vacuum as there are no particles and sound is created through changes in air pressure with the energy moving from particle to particle. The ringing bell is seen and heard from inside the bell jar. The pump is switched on and slowly all of the air is pumped out of the jar. and the sound is becoming fainter and fainter until it can hardly be heard at all.
     • Infrasound is the range below human hearing.
   • Sound and Ultrasound can be made to reflect.
     • Reflected Sound is called an Echo.
   • Ultrasound in medicine
     • The scan of a foetus - a probe sends out ultrasound waves and detects reflections.
     • Scanning soft tissues for diagnosis of cancer.
     • Removing harmful tartar from teeth.
     • Removing bladder stones by shattering them.
   • Ultrasound in Industry
     • Used by geophysicists to detect vital materials like oil and minerals underground in rock.
     • Scanning metal castings for faults & cracks.
     • Fish location by sea-going trawlers.
     • Oceanography to map the surface of the ocean floor.
   • Echo Principal
     • Ultrasound is transmitted, and then reflected by boundaries, such as shoals of fish.

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