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Hold grains on a stretched sheet and shout near it — the grains jump, without anything touching them. Sound is carrying energy.
In this Activity, we will experiment to see that sound carries energy by making grains jump on a stretched sheet.
- Stretch a rubber/cellophane sheet tightly over a wide container (Fig. 10.14).
- Sprinkle grains (rice, salt or chalk powder) evenly over the sheet.
- Make a loud sound near the container without touching it.
- Repeat with louder and softer sounds and different grains.
- A vibrating source transfers energy to the surrounding medium.
- Particles of the medium vibrate and collide , passing the energy along.
- This energy reaches the listener (or makes the grains jump).
In the propagation of a sound wave, it is the energy that is transferred, not the particles of the medium.
Microphones capture sound and convert sound energy into an electrical signal: sound waves make a thin diaphragm vibrate, producing the signal. A speaker does the opposite — an electrical signal vibrates a cone to produce sound. Together they let us record and replay sound faithfully.
5. When sound travels from a tuning fork to your ear, what reaches your ear? Answer: (ii) the energy carried by the sound waves — not the air particles or the fork material.
- Energy of sound — the energy carried by a sound wave through the medium, without the particles flowing along.
