# P1E

Revision for Physics

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## P1E Fast Facts

- The best emitters and absorbers are dull and black.

- The worst emitters and absorbers (therefore, the best reflectors) are shiny and white.

- Mobile phones use microwave signals.

- Properties of infrared radiation include: heats the surface of the food and is reflected by shiny surfaces,

- Infrared is absorbed only by particels on the surface of the food increasing their energy.

- This energy is transferred to the rest of the food by conduction and convection.

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## P1E Fast Facts

- Properties of microwave radiation include: they penetrate (about 1cm) into food and are reflected by shiny metal surfaces.

- Water and fat molecules absorb microwaves.

- Microwaves are absorbed only by water and fat in the outer layers of food increasing their kinetic energy.

- When microwaves transmit information there is some signal loss due to interference, the curvature of the Earth, no diffraction around objects and adverse weather.

- The evidence of dangers from mobile phones is not conclusive.

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## P1E Fast Facts

- Therefore it is not easy to decide on the sitting of phone masts.

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

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## Know the different views about the risk from mobil

- Some people think that the microwaves emitted into your body from using a mobile phone or living near a mobile phone mast could damage your health.

- There's no conclusive proof, there is conflicting evidence.

- People think that the microwaves can damage your brain cells causing diseases such as brain tumours and cancer.

- To reduce these risks people should: only make necessary phone calls, text instead and keep their mobile phone away from them when they are asleep at night so not underneath your pillow.

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## Explain how to reduce signal loss with microwaves

Microwaves have a shorter wavelength than radio waves, so they don't diffract much. This means they're affected by the curvature of the Earth because they don't bend round it like long-wave radio waves. It also means they're blocked more by large obstacles like hills because they can't bend round them.

This means that microwave transmitters need to be positioned in line of sight - they are usaully high up on hilltops so they can 'see each other' and they're positioned fairly close together.

If there is a hill or obstacles between the phone and the transmitter, you will probably get poor signal or no signal at all.

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