Question

Define intensity of sound.

Short answer

Sound intensity is the power per unit area carried by a sound wave, measured in watts per square meter (W/m²).

Step-by-step solution

Understanding Sound Intensity

Sound intensity is a measure of the power carried by sound waves per unit area in a direction perpendicular to that area. It quantifies how much sound energy passes through a certain area in a given amount of time.

Formula for Sound Intensity

The intensity of sound (I) is mathematically expressed by the formula: \[ I = \frac{P}{A} \] where I is the sound intensity, P is the power of the sound wave, and A is the area through which the sound power is passing.

Units of Sound Intensity

The unit of sound intensity in the International System of Units (SI) is watts per square meter (W/m²).

Key concepts

Sound Power

Sound power is the total energy that a sound source emits per second. It's an intrinsic property of the source, meaning it doesn't vary regardless of the environment. Sound power is measured in watts (W), which indicates how much energy is being produced per unit time. For example, when you speak, your vocal cords generate sound power which is then converted into sound waves traveling through the air.
The main difference between sound power and sound intensity is that sound power is the total output of the source, while sound intensity depends on how much of that power passes through a unit area at a certain distance from the source.
In formula form, it's the 'P' in the sound intensity formula \( I = \frac{P}{A} \). This helps us understand how energy is distributed through an area and ultimately perceived as sound.

Watts per Square Meter

Watts per square meter (W/m²) is the unit used to measure sound intensity. It shows how much sound power is passing through a given area. Imagine shining a flashlight on a wall; if you widen or narrow the beam, the brightness on the wall changes because the same amount of light spreads over a larger or smaller area. Similarly, sound intensity decreases as you move away from the source because the same amount of sound power spreads over a larger area.
Understanding W/m² is key to interpreting how loud a sound will be at various distances from its source. A higher value means louder sound. This is crucial in many practical applications, such as ensuring safe sound levels in workplaces or designing audio equipment.
In our formula, \( I = \frac{P}{A} \), the 'I' represents sound intensity measured in W/m².

Sound Waves

Sound waves are vibrations that travel through a medium like air, water, or solid materials. They are created when an object vibrates, causing the surrounding medium to compress and decompress in a wave-like pattern. These waves carry sound energy from one place to another.
Sound waves have several important characteristics:

• Frequency: Determines the pitch of the sound (measured in hertz, Hz).
• Amplitude: Relates to the volume or loudness.
• Wavelength: The distance between successive compressions or rarefactions.

Understanding sound waves is essential for grasping how sound intensity works. The waves' energy corresponds to sound power, and how this energy spreads through a given area (watts per square meter) determines the sound intensity.
Grasping these basics helps you understand why a whisper sounds different from a shout and why sound fades as you move further away from the source.