Free Waves And Sound Question and Answers — Questions and Answers

Question 1: The sound box on an acoustic guitar amplifies the volume of the sounds the strings produce. This results from the quality known as

Resonance (Correct answer)
Reflection
Amplification
Refraction

Correct answer: Resonance

Resonance is the phenomenon where an object's natural frequency is amplified by external vibrations, leading to a significant increase in sound amplitude. In an acoustic guitar, the vibrating strings cause the soundboard and the air within the sound box to resonate, effectively amplifying the sound and giving the instrument its characteristic volume and tone.

Question 2: An air column that is closed at one end has first and second resonant lengths of 15.5 cm and 45.5 cm, respectively. The ideal value for the wave's wavelength is

91 cm
60 cm (Correct answer)
62 cm
31 cm

Correct answer: 60 cm

For an air column closed at one end, the resonant lengths occur at odd multiples of a quarter wavelength (L = nλ/4, where n=1, 3, 5...). The first resonant length (n=1) is λ/4, and the second (n=3) is 3λ/4. The difference between these two resonant lengths is (3λ/4) - (λ/4) = λ/2. Given the lengths are 15.5 cm and 45.5 cm, λ/2 = 45.5 cm - 15.5 cm = 30 cm. Therefore, the full wavelength (λ) is 2 * 30 cm = 60 cm.

Question 3: When you pluck a guitar string, it creates waves that are

Longitudinal waves
Electromagnetic waves
Acoustic waves
Transverse waves (Correct answer)

Correct answer: Transverse waves

When a guitar string is plucked, the string itself vibrates up and down, or side to side, perpendicular to the direction the wave energy travels along the string. This type of wave, where the particles of the medium oscillate perpendicular to the direction of wave propagation, is defined as a transverse wave. While the sound waves produced in the air are longitudinal, the waves on the string are transverse.

Question 4: How many nodes should be present in the third overtone of standing waves created on a string with both ends fastened?

Two
Four
Five (Correct answer)
Six

Correct answer: Five

For standing waves on a string with both ends fastened, the number of nodes is always one more than the harmonic number. The fundamental frequency is the first harmonic, the first overtone is the second harmonic, and so on. Therefore, the third overtone corresponds to the fourth harmonic. For the fourth harmonic, there will be 4 + 1 = 5 nodes present on the string.

Question 5: In 25 seconds, a pendulum makes 75 swings. What time period is it?

3.0 Hz
3.0 s
0.33 Hz
0.33 s (Correct answer)

Correct answer: 0.33 s

The time period (T) of a pendulum is the time it takes to complete one full oscillation or swing. It is calculated by dividing the total time elapsed by the total number of swings. In this case, the pendulum makes 75 swings in 25 seconds, so T = 25 seconds / 75 swings = 0.333... seconds. Rounded to two decimal places, the time period is 0.33 s.

Question 6: What note's pitch is four octaves below 880 Hz at what frequency?

110 Hz
55 Hz (Correct answer)
880 Hz
220 Hz

Correct answer: 55 Hz

An octave represents a doubling or halving of frequency. To find a note four octaves below 880 Hz, you need to divide the frequency by 2 for each octave. This means dividing by 2 four times, which is equivalent to dividing by 2^4 or 16. Therefore, the frequency is 880 Hz / 16 = 55 Hz.

Question 7: Which of the following could result from completely harmful interference?

Node (Correct answer)
Antinode
Supercrest
Supernode

Correct answer: Node

Completely harmful interference, also known as destructive interference, occurs when two waves combine perfectly out of phase, causing their amplitudes to cancel each other out. A node is a specific point in a standing wave where the displacement or amplitude of the wave is always zero due to this complete destructive interference. It represents a point of no vibration.

Free Waves And Sound Question and Answers

The sound box on an acoustic guitar amplifies the volume of the sounds the strings produce.
This results from the quality known as