The energy arriving at a SQUARE METRE of surface per second is a useful measure of the strength (or the INTENSITY) of a beam of electromagnetic radiation.
The INTENSITY depends on the number of photons delivered per second and the amount of energy each individual packet, i.e. the photon energy.
This decrease in intensity is due to three factors in GCSE physics:
- As the photons spread out from the source, they are more thinly spread out when they reach the detector.
- Some of the photons are absorbed by particles in the substances they pass through
- Some of the photons are reflected and scattered by other particles
These effects combine to reduce the number of photons arriving per second at a detector, resulting in a lower measured intensity.
When a material absorbs radiation, it will HEAT up:
- The temperature increase depends on the intensity of the radiation
- The amount of heating also depends on the duration of exposure
Some electromagnetic radiations (ULTRAVIOLET, X-RAYS, GAMMA RAYS) have enough energy to change atoms or molecules – These changes can initiate a chemical reaction.
Some materials (radioactive materials) emit ionising gamma radiation all the time. Ionising radiation has photons with enough energy to remove an electron from an atom or molecule to form ions.
End of unit 2.1! See you in next unit!
Drafted by Gina (Physics)