P1e

P1e

1. The best emitters and absorbers are dull and black.

2. The worst emitters and absorbers (and also best reflectors) are shiny and white.

3. Mobile Phones

   • Mobile phones use microwave signals.
     • When microwaves transmit information there is some signal loss due to interference, he curvature of the earth, no diffraction around objects and adverse weather.
       • To reduce signal loss you should put microwave aerials for sending telephone signals on high buildings or towers pointing in every direction.
   • The evidence of dangers from mobile phones is not conclusive.
     • At the moment there is no scientific proof of the dangers of mobile phones. There is some evidence of warming and rats show signs of stress near mobile phones.
     • It is not easy to decide the sitting of phone masts.

4. Infrared Radiation

   • Properties of infrared radiation include: heats the surface of food and is reflected by shiny surfaces.
   • Infrared is absorbed only by particles on the surface of the food increasing their energy.
     • This energy is then transferred to the rest of the food by conduction and convection.

5. Microwave Radiation

   • Properties of microwave radiation include: they penetrate (about 1cm) into food, are reflected by shiny metal surfaces, can cause burns when absorbed by body tissue and can pass through glass and plastics.
   • Water and fat absorb microwaves.
     • Microwaves are absorbed only by water and fat in the outer layers of the food increasing their KE.

6. As you increase the frequency of a microwave the energy increases.