Exploring Structure Using Waves (HT only)
- Sound waves can be used to analyse structures that are hidden from direct observation
- Examples of the use of sound waves
- Echo sounding used by shipping to detect the ocean floor
- Ultrasound used to look inside the human body
- Ultrasound crack detection to find cracks in rail tracks
- Reflection seismology to detect oil and gas underground
- Seismic activity (Earthquakes) can be used to investigate the structure of the Earth
- The properties of a substance that allow the detection of hidden structures are:
- Reflection
- Absorption
- Transmission
- The speed of sound in the substance
- Each type of substance will produce different amounts of reflection, absorption and transmission
- Each type of substance will also transmit a sound wave at a specific speed
- Sounds will travel faster in solids than liquids and sound travels faster in liquids than gases
- Certain structures will reflect a proportion of the sound wave and transmit the rest
- Some substances will absorb sound waves with very little reflection
- By detecting the amount of sound reflected and the speed of the wave the hidden structure can be identified
In my experience of teaching GCSE Physics students, exploring structures using waves is another one of those topics that students often struggle with because it is hard to visualise. To help them with this, I would ask my students to push some desks and chairs to the back of the classroom in a random arrangement. This would represent an undulating seabed. I asked the students to stand on the other side of the classroom where they represented the surface of the water and I asked them to clap in a steady rhythm. A volunteer would walk towards the ‘seabed’ in time with the beat of the claps. When the student touched the ‘seabed’ they turned around and walked back, keeping to the beat.
In this demonstration, the student represented the sound waves travelling at the same constant speed (the speed of sound in water). They found that it took longer for the student to return to the surface where the water was deeper. This is how echo sounding works to map the seabed. Sound waves are sent out at the same time, at the same speed, and the sound waves return at different times. We use this information to determine the different depths of the seabed and create an image. As a teacher, I find that making abstract concepts tangible, really helps to aid understanding.
