Physics 4D

Physics 4D

1. Key Processes

   • Transverse waves
     • In transverse waves, the oscillations (vibrations) are at right angles to the direction of travel and energy transfer Light and other types of electromagnetic radiation are transverse waves. All types of electromagnetic waves travel at the same speed through a vacuum, such as through space
   • Longitudinal waves
     • In longitudinal waves, the oscillations are along the same direction as the direction of travel and energy transfer
       • Sound waves and waves in a stretched spring are longitudinal waves. P waves (relatively fast moving longitudinal seismic waves that travel through liquids and solids) are also longitudinal waves
         • Longitudinal waves show area of compression and rarefaction. In the animation, the areas of compression are where the parts of the spring are close together, while the areas of rarefaction are where they are far apart
   • Ultrasound
     • Babies
       • Ultrasound may be used instead of x-rays for certain scans, such as scan of unborn babies. Compared to x-ray photographs, ultrasound scans do not damage living cells and produce images of soft tissue
       • Ultrasound is sent into the patient's body. Some of the ultrasound is reflected at each boundary between different tissues or organs. The depth of each layer is calculated using the time taken for each reflected wave to return. The reflected waves (echoes) are usually processed to produce a picture of the inside of the body on a screen
       • The ultrasound waves used to image babies and soft tissue organs have small amplitude so are low energy. This makes it safer for the patient, as no damage is done to any living cells
     • Kidney Stones
       • A high powered ultrasound wave is used to break down kidney stones and other stones in the body. The stones vibrate until they shake themselves apart and are then easily passed out of the body via the urethra
   • Definitions
     • Amplitude - The maximum distance the particles move from their normal position. The louder a sound is, the more energy it carries and the bigger its amplitude
     • Wavelength - The distance between one high pressure region (compression) and the next
     • Frequency - The number of waves produced in one second, measured in hertz, Hz. A higher pitched sound has a higher frequency than a lower pitched sound
     • Compression - A region of higher pressure where particles are squashed together
     • Rarefaction - A region of lower pressure where particles are spread out

2. Sound is produced by vibrating particles

3. Longitudinal waves vibrate parallel to the motion of the wave(e.g sound)

4. Transverse waves vibrate at right angles to the motion of the wave

5. Frequency is the number of complete waves in a second. It is measured in Hertz, Hz

6. Ultrasound is sound with a higher frequency than Humans can hear

7. The upper threshold for human hearing is 20,000Hz

8. Ultrasound can be used to scan the body to make images of the organs, foetuses or tumours

9. Ultrasound can be used to break down kidney stones and break up cataracts in the eye