Test: Characteristics Of Sound Waves - Class 9 MCQ

We know that, T = 1 / f
Where, f is the frequency, T is time period
Also, Speed  =  Distance / Time taken
Speed of wave is it's velocity v, and Distance of wave is it's wavelength lemda. 
Substituting these into the equation. 
=>  v = lemda / T
=>    v  = lemda  f 
As,  T =  1/ f
Therefore,  v = f lemda

Wavelength = speed of air (v) / frequency (ν)

Wavelength = 320/ 450= 0.711 m

Number of holes h = 16
Revolutions per minute = 960

Revolutions per second =960/60 =16

frequency = no. of holes x revolutions per sec

= 16 x16 =256 Hz

The  hertz (symbol Hz) is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon.

This unit is named after a German physicist Heinrich Hertz.

The speed of sound decreases as we go from solid to gaseous state because the density of particles decreases from solid to gaseous.

 

In 0.4 sec=16 rotations,

so in, 1 sec = 16/0.4

=160/4

=40 rotations

The pitch of sound depends on the frequency of vibration. The higher the frequency the more shrill is the sound and vice versa.

High pitch sound is a sound which has a high frequency. usually shrill sounds have a high pitch. for ex. a whistle has high pitch.

low pitch sounds are sounds which have low frequency rate. for ex. horse voice.

loud sounds have a high amplitude. for ex. a mega phone gives sound of high amplitude.

soft sounds are sounds which have low amplitude. for ex. a birds chirping has low amplitude.

Compression is the region of high pressure and rarefaction is the region of low pressure. Higher the pressure in a region, higher is the number of particles per unit volume and hence higher is the density of the medium. So, a sound wave propagates through a medium as the variation in its pressure or density.

 

Pitch of sound is how brain interprets the frequency of the emitted sound. In harmonica, vibration of particles is more at the source, and hence more frequency. Therefore, it has higher pitch. Thus, harmonica sound appears different than sound of flute

Given:
Frequency of the whistle = 2600 Hz
Distance from the engine to the person = 550 m
To find the number of waves heard by the person in one minute, we need to convert the frequency from Hz to waves per minute.
Step 1: Convert frequency to waves per second:
- The frequency of the whistle is given in Hz, which represents the number of waves produced per second.
- Therefore, the number of waves per second can be calculated as follows:
Waves per second = Frequency (Hz) = 2600 Hz
Step 2: Convert waves per second to waves per minute:
- Since we need to find the number of waves heard in one minute, we need to convert waves per second to waves per minute.
- There are 60 seconds in a minute, so the conversion can be done by multiplying waves per second by 60:
Waves per minute = Waves per second x 60 = 2600 Hz x 60 = 156000 waves/minute
Therefore, the person standing at a distance of 550 m from the engine will listen to 156 x 10^3 waves within one minute.
Hence, the answer is option A: 156 x 10^3.

When the temperature increases then the kinetic energy of the particles also increases as a result they move more faster and so the energy is more fastly transferred through the molecules of the medium.

A compression is a region in a longitudinal wave where the particles are closest together. A rarefaction is a region in a longitudinal wave where the particles are furthest apart.

Counting Vibrations of a Tuning Fork
The number of vibrations of a tuning fork per second can provide information about the frequency of the wave. Here's a detailed explanation:
Frequency of a Wave:
- The frequency of a wave refers to the number of complete vibrations or cycles that occur in one second.
- It is typically measured in Hertz (Hz) or cycles per second.
- The frequency determines the pitch of a sound wave, with higher frequencies corresponding to higher pitches and lower frequencies corresponding to lower pitches.
Counting Vibrations:
- A tuning fork is a device that produces a specific pitch or frequency when struck.
- By counting the number of vibrations the tuning fork makes in one second, we can determine the frequency of the wave it produces.
- This can be done using various methods, such as using a stopwatch or a device specifically designed to measure frequency.
Importance of Frequency:
- The frequency of a sound wave is one of its fundamental characteristics.
- It helps us differentiate between different sounds and determine their pitch.
- By measuring the frequency of a tuning fork, we can compare it to the expected frequency and determine if it is in tune or not.
In conclusion, by counting the number of vibrations of a tuning fork per second, we can find the frequency of the wave it produces. This information is important for understanding the pitch of the sound and for tuning musical instruments.

Oscillation  = time / time period 
⇒ 84 second / 1.4 second 
⇒ 60

When waves travel from one medium to another the frequency never changes. As waves travel into the denser medium, they slow down & wavelength decreases. Part of the wave travels faster for longer causing the wave to turn. The wave is slower but the wavelength is shorter means frequency remains the same.

The only sound which consists of a single frequency is the pure SINE TONE such as produced by a sine wave OSCILLATOR or approximated by a tuning fork. All other sounds are complex, consisting of a number of frequencies of greater or lesser intensity. The frequency content of a sound is its SPECTRUM.