# How Frequency Determines the Pitch of Sound Waves

Sound is a form of energy that travels through a medium as a wave. A sound wave consists of alternating regions of high and low pressure, called compressions and rarefactions. When a sound wave reaches our ears, it causes our eardrums to vibrate, which is then converted into electrical signals by the auditory nerve and sent to the brain. The brain interprets these signals as sound.

One of the characteristics of sound waves that affects how we perceive sound is frequency. Frequency is the number of cycles or oscillations of a wave per unit time. It is measured in hertz (Hz), which is equivalent to one cycle per second. The frequency of a sound wave determines its pitch, which is how high or low a sound seems to us.

## High Frequency, High Pitch

Sound waves with high frequency have a high pitch and sound waves with low frequency have a low pitch. For example, a whistle has a high frequency and a high pitch, while a drum has a low frequency and a low pitch. The human ear can hear sounds with frequencies ranging from about 20 Hz to 20,000 Hz, depending on the age and health of the person. Sounds with frequencies below 20 Hz are called infrasound and sounds with frequencies above 20,000 Hz are called ultrasound. These sounds are not audible to humans, but some animals can hear them.

The frequency of a sound wave depends on the source of the sound and the medium it travels through. For example, when you pluck a guitar string, it vibrates at a certain frequency, which depends on the length, tension, and mass of the string. The vibrating string produces sound waves that travel through the air and reach our ears. The air molecules also vibrate at the same frequency as the string, transferring the energy of the sound wave.

## How to Change the Frequency of Sound Waves

There are several ways to change the frequency of sound waves produced by a source or perceived by an observer. Some of these methods are:

• Changing the speed of the source or the observer: This causes an effect known as Doppler effect, which is the apparent change in frequency due to relative motion between the source and the observer. For example, when an ambulance with a siren approaches you, you hear a higher pitch than when it moves away from you. This is because as the ambulance comes closer, the sound waves reach your ears more frequently than when it moves away.
• Changing the temperature or pressure of the medium: This affects the speed of sound in the medium, which in turn affects the wavelength and frequency of sound waves. For example, sound travels faster in warm air than in cold air, which means that sound waves have shorter wavelengths and higher frequencies in warm air than in cold air.
• Changing the shape or size of the source: This affects the natural frequency or resonance of the source, which is the frequency at which it vibrates most easily. For example, when you blow into a bottle, it produces a sound with a certain pitch that depends on how much air is inside the bottle. If you fill or empty some air from the bottle, you change its resonance and its pitch.

## Why Frequency Matters

Frequency is an important property of sound waves because it affects how we perceive and identify different sounds. For example, we can distinguish between different musical instruments or different voices based on their frequencies. We can also use frequency to communicate information or emotions through speech or music. Frequency can also be used for scientific or technological purposes, such as measuring distances or detecting objects using sonar or radar.

According to Testbook.com, pitch is determined by the frequency of the sound wave. Sound waves with high frequency have a high pitch and sound waves with low frequency have a low pitch. In human beings, women have a high pitch whereas men have a low pitch.