The diagram shows a signal generator connected to two loudspeakers emitting the same note - Leaving Cert Physics - Question 8 - 2008

This effect occurs due to the inverse square law, which states that sound intensity decreases with the square of the distance from the source. Additionally, any interference patterns may also occur due to the sound waves overlapping.

This phenomenon indicates that sound is a wave and demonstrates the propagation of sound waves through a medium and how distance from the source affects sound intensity.

To demonstrate that sound requires a medium to travel, the following experiment can be conducted:

1. Set up an electric bell in a vacuum bell jar connected to a battery.
2. Turn on the bell, and observe it ringing while air is present in the jar. Sound is heard clearly.
3. Then, use a vacuum pump to remove air from the jar.
4. Once the air has been evacuated, try to ring the bell again. It will ring but sound cannot be heard inside the jar, proving that sound needs a medium as it cannot travel in a vacuum.

Doppler effect.

The Doppler effect occurs due to the relative motion between a sound source and an observer. As the sound source approaches the observer, the sound waves are compressed, resulting in a higher frequency (or pitch) perceived by the observer. Conversely, as the source moves away, the waves are stretched, resulting in a lower frequency.

An application of the Doppler effect can be observed in radar and sonar technologies, where it is used for measuring speed. For instance, police radar guns utilize this effect to measure the speed of a moving vehicle by detecting the frequency change in the returning radar waves.