Sound

10.1 Production of sound by vibrations The tuning fork vibrates and you hear a sound. Sounds are made when an object vibrates. Sounds is a form of energy that produces sense of hearing.

10.2 Transmission of sound in terms of compressions & rarefactions Longitudinal Wave wave particles vibrate back and forth along the path that the wave travels. Compression Wave

Compressions The close together part of the wave Rarefactions The spread-out parts of a wave

The Loudspeaker The Loudspeaker The compressions and rarefactions move away from the speaker as sound waves

10.3Human range of audible frequencies

How sound reaches to us ? 1. Sound waves are collected by the outer ear (or pinna). 6.The auditory nerve takes the signals to the brain. 4. The small bones (ossicles) amplify the vibrations. 2. The waves travel along the ear canal. 3. The waves reach the eardrum and make it vibrate. 5. The cochlea turns these into electrical signals. 9

Range of Hearing Human beings can hear sound frequencies between 20 Hz and 20 KHz. Sound whose frequency is less than 20 Hz is called infrasonic sound. Animals like dogs, elephants, rhinoceros, whales etc. produce and hear infrasonic sound. Sound whose frequency is more than 20000 Hz is called ultrasonic sound. Animals like dolphins, bats, rats porpoises etc. produce and hear ultrasonic sound. Bats use reflection of ultrasonic sound waves to detect an obstacle or its prey.

Comparing hearing ranges Which animals hear the lowest and the highest frequencies? 100,000 10,000 1,000 100 10 1 frequency (Hz) Frequency low (Hz) high (Hz) Human 20 20 000 Dog 40 45 000 Bat 1000 150 000 Elephant 1 20 000 Mouse 1000 100 000 Cat 100 60 000 Dolphin 70 150 000 human dog bat elephant mouse dolphin

10.4 Sound need medium to travel The bell-jar experiment vacuum pump on

10.6 Order of magnitude of speed of sound in different medium The speed at which it travels though a material will therefore depend on how close together the molecules are, and so upon the density of a material - the more tightly packed the molecules, the more quickly vibrations can be transferred from molecule to molecule, i.e. the faster the sound can travel though the material.

Speed of sound in different materials The speed of sound is approximately: 340m/s in air - gas molecules are relatively far apart, and the transfer of vibrations (sound) is relatively slow 1400m/s in water - liquid molecules are much closer together, and transfer of vibrations is much more rapid 6000m/s in steel - solid molecules are even closer together, and transfer of vibrations is even more rapid

Sound in different materials Sound needs a substance through which to travel because it travels by making particles vibrate. Which state of matter does sound travel fastest through? Sound waves travel fastest through solids. The particles in a solid are closer together than in a gas, and more tightly bound than in a liquid. This means vibrations are more easily passed from particle to particle, and so sound travels faster. 15

Sound waves in different materials

10.7 Technical terminology of Sound Amplitude- maximum distance the particles in a wave vibrate from their rest positions. Frequency number of waves produced in a given time

Sound Wave

The louder the sound, the greater the amplitude. What is the difference between the sound wave of a quiet sound and a loud sound? quiet sound loud sound The loud sound has taller waves. The louder the sound, the greater the amplitude.

What is the difference between the sound wave of a low pitch sound and a high pitch sound? The high pitch sound has a shorter wavelength, so more waves are visible. It has higher frequency waves.

Frequency  Pitch Amplitude  Loudness Loudness The loudness of a sound increases with the amplitude of the sound wave. loud quiet

The pitch increases with frequency. low pitch high pitch .

Match the description to the oscilloscope pattern: B C D 1. Low-pitched sound, very loud D 2. Loud, high-pitched sound C 3. Medium sound with medium pitch B 4. Quiet, high-pitched sound A

Echo If we shout or clap near a reflecting surface like tall building or a mountain, we hear the same sound again. This sound which we hear is called echo. It is caused due to the reflection of sound. To hear an echo clearly, the time interval between the original sound and the echo must be at least 0.1 s. Since the speed of sound in air is 344 m/s, the distance travelled by sound in 0.I s = 344 m/s x 0.1 s = 34.4 m So to hear an echo clearly, the minimum distance of the reflecting surface should be half this distance, that is 17.2 m. Reverberation Echoes may be heard more than once due to repeated or multiple reflections of sound from several reflecting surfaces. This causes persistence of sound called reverberation. In big halls or auditoriums to reduce reverberation, the roofs and walls are covered by sound absorbing materials like compressed fiber boards, rough plaster or draperies.

Quizenia

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