When a musician moves his fingers up and down the strings of a guitar, the frequency of the note changes. When the strings are at their longest, the note heard has a low frequency. The characteristics of a musical note are pitch, loudness and quality. (i) Which of these characteristics can be quantified as a frequency? (ii) Name the property of a wave that affects its loudness. (iii) When the musician plays the A string on his guitar, the frequency of the note is 110 Hz. The speed of sound in air is 340 m s⁻¹. What is the wavelength of the note? (iv) Describe an experiment to show that sound cannot travel through a vacuum. (v) The frequency of a sound wave appears to change when it moves past a stationary observer. This phenomenon is called the Doppler effect. (vi) Describe how to demonstrate the Doppler effect in a laboratory. (vii) Sound can be described as a longitudinal wave, whereas light is a transverse wave. Distinguish between a longitudinal wave and a transverse wave. A labelled diagram may help your answer. Waves can undergo reflection, refraction, diffraction, interference and polarisation. While light waves can undergo all of these five phenomena, sound waves can only undergo four of them. (vii) Which one of these phenomena do sound waves not undergo? Explain why.

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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

Question 7

When a musician moves his fingers up and down the strings of a guitar, the frequency of the note changes. When the strings are at their longest, the note heard has a... show full transcript

Worked Solution & Example Answer: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

Step 1

Which of these characteristics can be quantified as a frequency?

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Answer

The characteristic that can be quantified as a frequency is pitch. Pitch is directly related to the frequency of sound waves; higher frequencies correspond to higher pitches.

Step 2

Name the property of a wave that affects its loudness.

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Answer

The property of a wave that affects its loudness is amplitude. Higher amplitude waves correspond to louder sounds.

Step 3

When the musician plays the A string on his guitar, the frequency of the note is 110 Hz. The speed of sound in air is 340 m s⁻¹. What is the wavelength of the note?

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Answer

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

ext{Speed} = ext{Frequency} imes ext{Wavelength}

Rearranging gives us:

\lambda = \frac{\text{Speed}}{\text{Frequency}} = \frac{340 \, \text{m/s}}{110 \, \text{Hz}} \approx 3.09 \, ext{m}

Step 4

Describe an experiment to show that sound cannot travel through a vacuum.

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Answer

One experiment to demonstrate that sound cannot travel through a vacuum involves using a bell in a bell jar.

Apparatus: A bell, a vacuum pump, and a bell jar.

Procedure:

Place a sound-producing bell inside the bell jar.
Use a vacuum pump to remove the air from the jar.
As the air is pumped out, observe the bell while it rings.

Observation: As the air is evacuated, the sound becomes less audible and eventually cannot be heard, thus demonstrating that sound requires a medium (air) to travel.

Step 5

Describe how to demonstrate the Doppler effect in a laboratory.

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Answer

To demonstrate the Doppler effect, one effective method is to use a moving sound source.

Apparatus: A sound source (like a siren) and a track to move it along.

Procedure:

Position the sound source on a track and ensure it can move towards and away from a stationary observer.
As the sound source approaches the observer, note that the frequency of the sound appears higher; as it moves away, the frequency appears lower.

Conclusion: This change in perceived frequency as the source moves is the Doppler effect.

Step 6

Distinguish between a longitudinal wave and a transverse wave. A labelled diagram may help your answer.

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Answer

Longitudinal waves are waves in which the particles of the medium move parallel to the direction of the wave propagation, such as sound waves. Transverse waves have particles that move perpendicular to the direction of wave propagation, such as light waves.

A labelled diagram should illustrate the oscillations of particles for both types of waves, indicating the direction of wave travel for both longitudinal and transverse modes.

Step 7

Which one of these phenomena do sound waves not undergo? Explain why.

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Answer

Sound waves do not undergo polarisation. This phenomenon is characteristic of transverse waves, where oscillations can occur in only a single plane. Since sound is a longitudinal wave, its particles only move back and forth in the same direction as the wave, thus preventing it from being polarised.

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

Worked Solution & Example Answer: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

Which of these characteristics can be quantified as a frequency?

Name the property of a wave that affects its loudness.

When the musician plays the A string on his guitar, the frequency of the note is 110 Hz. The speed of sound in air is 340 m s⁻¹. What is the wavelength of the note?

Describe an experiment to show that sound cannot travel through a vacuum.

Describe how to demonstrate the Doppler effect in a laboratory.

Distinguish between a longitudinal wave and a transverse wave. A labelled diagram may help your answer.

Which one of these phenomena do sound waves not undergo? Explain why.

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