When a musician moves his fingers up and down the strings of a guitar, the frequency of the note changes - Leaving Cert Physics - Question 7 - 2019

The amplitude of a wave affects its loudness. A higher amplitude corresponds to a louder sound, while a lower amplitude results in a quieter sound.

To find the wavelength ( ( \lambda ) ) of the note, we can use the formula:

$v = f \cdot \lambda$

where:

• (v) is the speed of sound (340 m/s)
• (f) is the frequency (110 Hz)

Rearranging for ( \lambda ): $\lambda = \frac{v}{f} = \frac{340 \, \text{m/s}}{110 \, \text{Hz}} \approx 3.09 \, \text{m}$

Apparatus:

• A bell jar or a sound source like an electric bell
• A vacuum pump

Procedure:

1. Place the electric bell inside the bell jar.
2. Seal the jar and start the vacuum pump to remove the air.
3. Observe the sound produced by the bell as the air is pumped out.

Observation/Conclusion: As air is removed, the sound becomes quieter until it is no longer heard, demonstrating that sound cannot travel through a vacuum.

You can demonstrate the Doppler effect using a sound source, like a tuning fork or a moving vehicle: 1. Place a sound source at one end of a long, open area. 2. Move the sound source towards a stationary observer while producing sound. 3. As the source approaches, the pitch will seem higher; as it moves away, the pitch will seem lower. This change in frequency is the Doppler effect.

Longitudinal waves are waves where the particle displacement is parallel to the direction of wave propagation (e.g., sound waves). In contrast, transverse waves have particle displacement that is perpendicular to the direction of wave propagation (e.g., light waves).

A labelled diagram should show:

• Longitudinal wave: Compressions and rarefactions.
• Transverse wave: Crests and troughs.

Sound waves do not undergo polarisation. This is because polarisation requires a transverse wave; sound waves are longitudinal and consist of compressions and rarefactions, not orientations of vibrations that can be filtered.