National 5 - Physics Unit 2 waves & Radiation

National 5 - Physics Unit 2 waves & Radiation

1. types of waves?

   • Transverse- Particles move up and down at 90 degrees to wave direction. -examples: water waves and electromagnetic spectrum
   • Longitudinal- particles move along wave direction -examples: sound waves and ultra sound
   • What are waves?
     • They are created by vibrations and transfer energy

2. Electromagnetic spectrum

   • Radio-Microwaves-Infrared-Visible-Ultraviolet-X rays-Gamma
     • speed=3x10^8ms-1

3. Definitions

   • Frequency?
     • The amount of waves to pass a point in 1 second
     • equation?
       • f=number/time
   • wavelength?
     • The length of one complete wave (lambda)
   • Period?
     • The time taken to produce one complete wave (seconds)
   • Amplitude?
     • The amount of energy carried by a wave (measured from the mid point to peak or trough)

4. Diffraction?

   • When a wave meets an obstacle and bends to some extent.

5. Refraction?

   • change in speed of light as it travels from one material to another
   • Angle of incidence- between the ray that is entering material and the normal. Angle of refraction- between ray in material and normal. Critical angle- when one ray is parallel to material the le between other ray and normal
   • In more dense materials light refracts towards normal. In less dense materials light refracts away from normal

6. Radioactivity

   • When is an element radioactive?
     • When an elements mass number becomes too large its proton-neutron ratio falls out of the band of stability. It begins to emit radiation in order to become stable again
   • Alpha
     • Helium nucleus- 2 protons 2 neutrons -very ionising -absorbed by paper, skin or a few cm of air
       • Polonium-210 used in smoke alrms
   • Beta
     • fast moving electron- ionising -absorbed by few cm of aluminium
       • Strontium-90 used for thickness control
   • Gamma
     • EM wave- least ionising- passes through body -absorbed by several cm of lead
       • Cobalt-60 killing cancer cells
   • ionisation?
     • when an atom looses or gains electrons to become charged
   • Activity= the number of radioactive decays each second (Bq)
   • Background Radiation
     • Natural?
       • Rocks Food Cosmic Rays
     • Artificial?
       • Medical treatments Nuclear waste Weapons testing
   • Half-life
     • the time taken for half the nuclei in a radioactive source to decay
   • Precautions
     • USe tongs, wear gloves, wash hands
   • nuclear...
     • fisson
       • bombarding a uranium atom with a slow neuron producing two or more smaller atoms, fast neutrons, and energy
     • fusion
       • joining two small nuclei to form a larger nucleus releasing a large amount of energy and no radioactive waste. takes place in sun and stars

7. Dosimetry

   • Damage done to tissue depends on...
     • Type of tissue type of radiation and amount of energy/radiation
   • Absorbed Dose
     • the energy absorbed per unit mass
     • can reduce it by- shielding, increasing d from source and limiting time with source
   • Equivalent dose
     • the bio harm caused by radiation
     • We need to measure the rate of this to prevent people from experiencing too much exposure in a short period of time

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