Sound

1. The wavelength of a sound wave is 3 cm and speed of sound
is 340 ms−1. Will it be audible? [2 MARKS]
Solution
Formula : 1 Mark
Result : 1 Mark
Speed=wavelength×frequency
340=0.3×Frequency
∴Frequency =3400.3 = 1133.33 Hz.
It will be audible because frequency range of a human ear is
20 Hz to 20000 Hz.

2. How are compressions and rarefactions produced in air
near a source of sound?
Sound is a mechanical wave and needs a medium to travel.
The vibrations created travel parallel to the direction of
propagation of sound and thus create regions of high and
low pressures.
When a vibrating object moves forward, it pushes and
compresses the air in front of it creating a region of high
pressure. This region is called a compression (C). This
compression starts to move away from the vibrating
object.
When the vibrating object moves backwards, it creates a
region of low pressure called rarefaction (R).

3. Explain the difference between low pitched and high pitched sound using diagrams. [3
MARKS]
Solution
How the brain interprets the frequency of an emitted sound is called the pitch. The faster
the vibration of the source, the higher is the frequency and the higher is the pitch. Thus, a
high pitch sound corresponds to more number of compressions and rarefactions passing
a fixed point per unit time. Conversely, a low pitched sound has a lesser frequency.

4. Q.2 Mention five characteristics of sound waves
Sound waves are characterized by the following properties:
1. Wavelength : The distance between two consecutive crests of a wave is called
Wavelength.
2. Time period : The time taken by the wave to travel one wavelength is called its Time
period. Frequency is the reciprocal of time period.
3. Amplitude : The maximum distance travelled by a point of wave from its mean
position is called its Amplitude.
4. Mechanical Nature : Sound waves are called mechanical waves since they require a
medium for propagation.
5. Longitudinal Nature : Sound waves are vibrations which travel parallel to the

5. What do you mean by the frequency of a sound wave? [1 MARK]
Solution
When sound is propagated through a medium, the density of the
medium oscillates between a maximum value and a minimum value.
The change in density from the maximum value to the minimum
value, again to the maximum value, makes one complete oscillation.
The number of such oscillations per unit time is the frequency of the
sound wave.