| What is sound? | longitudinal waves. They cause particles to vibrate parallel to the direction of wave travel. The vibrations can travel through solids, liquids or gases. The speed of sound depends on the medium through which it is travelling. When travelling through air, the speed of sound is about 330 metres per second (m/s). Sound cannot travel through a vacuum because there are no particles to carry the vibrations. |
| How does the human ear detect spund? | Sound waves enter the ear canal and cause the eardrum to vibrate. Three small bones transmit these vibrations to the cochlea. This produces electrical signals which pass through the auditory nerve to the brain, where they are interpreted as sound. |
| Describe the amplitude and frequency of sound. | frequency - high frequency sound waves are high pitched, low frequency sound waves are low pitched
amplitude - low amplitude sound waves are quiet |
| What is ultra sound | waves that have a frequency higher than the upper limit for human hearing - above 20,000 Hertz (Hz). |
| Give 2 uses of ultrasound | 1)breaking kidney stones
2)cleaning jewellery |
| How does ultrasound imaging work? | A picture is formed when ultrasound waves meet the boundary between two different materials:
1)some of the ultrasound waves are reflected at the boundary
2)the time taken for the waves to leave a source and return to a detector is measured
3)the depth of the boundary can be determined using the speed of sound in the material and the time taken |
| Compare P and S waves? | P-longitudinal-faster-through solids and liquids
S-transverse-slower-solids only |
| What do the waves suggest about earths structure | S-waves are not detected on the opposite side of the Earth - this suggests that the mantle has solid properties, but the outer core must be liquid.
P-waves are detected on the opposite side of the Earth. Refractions between layers cause two shadow zones where no P-waves are detected. The size and positions of these shadow zones indicate there is a solid inner core. |
