Waves

WAVES are everywhere. We encounter them on a daily basis. Examples of waves are:

Sound Waves Light Waves Radio Waves Water Waves Waves on a String

But what is a

WAVE ??

WAVE - a disturbance traveling through a medium or in a

vacuum from one location to another.

SOUND WAVES

What is life without sound??? Quite unimaginable, for sound is there every moment of our life. But very seldom do we take time out to ponder the characteristics and behavior of sounds and the way they are produced.

What is SOUND WAVES???

Let’s take a look…

Sound Waves – is a longitudinal wave created by vibrating solids, liquids or gases and capable of producing a sensation in our auditory system. It can travel through a medium from one location to another. It travels at a speed of 331m/s in air at sea level when the temperature is 0 degree.

Wave Properties of Sound

A sound wave traveling in one medium may be partly reflected, refracted or absorb when it strikes another medium. Sound also exhibits the properties of diffraction, interference and the Doppler effect.

1. Reflection of Waves

The waves bounce back when a train of waves encounters a barrier. They are said to be reflected.

Sound waves may be reflected from walls, mountains, the ground and other objects. The direction of reflected sounds may be accurately predicted using the basic law of reflection. The angle of incidence = the angle of reflection

Angle of Incidence – angle between the incident wave and the normal to the reflecting surface.

Angle of Reflection – angle between the reflected waves and the normal. We call the reflection of sound “echo”.› Echo is the sound used by SONAR or Sound

Navigation Ranging in detecting and locating object. SONAR devices emits sound and measure the time required for the echo to return. SONAR is used to determine the depth of water.

2. Refraction of Waves

Refraction occurs whenever sound passes from one medium into another, where it changes its velocity.

During daytime when the air need the ground is warmer than the air above, sound is refracted from the ground, while at night, the reverse happens. That is why we hear better at night than during the day.

3. Diffraction of Waves

The ability of waves to travel around the corners or obstacles in their path is what we called as diffraction. It can be easily observed because the wave width of the opening, or size of the obstacle, is nearly the same order as the wavelength of sound.

4. Interference of Waves

Constructive interference – two pulses moving in opposite direction along a stretched string are unaffected by their crossing.

Destructive interference – complete cancellation occurs when identical pulses with opposite displacement by the edges of the barrier.

5. Doppler Effect

The Doppler effect is the apparent change in the frequency of sound due to the motion of source of sound and/or the observer.

Characteristic of Sound Waves

Sound may be described by four perceptual characteristics:

Pitch – refers to the highness or lowness of a sound. It depends upon the frequency of the sounding object. Higher frequency sounds produce high pitch while lower frequency sounds produce low pitch.

Loudness – is a physiological sensation that varies from one person to another. It depends on the sense of hearing, the distance from the source and the material through which the sound travels.

Intensity – depends on the amplitude of pressure variations within the sound waves. The unit for this is decibel(dB), named after Alexander Graham Bell.

Quality – property of a tone that distinguishes it from another tone of the same pitch and intensity produced by a different instrument. It enables you to identify the source of sound because tones differ from one another.

The Human Ear

The ear is our organ of hearing. It is divided into three parts: outer, middle and inner.

Parts of the Ear The outer ear is shaped like a funnel and is

called the pinna or auricle. It is that part of our ear that we have at the side of our head.

The middle ear is an air-filled space containing the eardrum or tympanic membrane, the Eustachian tube and the bridge of auricles. The eardrum separates the outer ear from the middle ear.

The inner ear contains a coiled fluid-filled tube called the cochlea.

Human perception of Sound

The pinna collects the sound waves and transmits them to the auditory canal. The auditory canal acts like a closed-tube amplifier producing a resonant frequency with a wave length equal to four times its length. The sound waves push on the eardrum. The pressure variation resulting from the compression and rare fractions in sound waves causes the eardrum to vibrate. These vibrations are transmitted to the liquid in the inner ear. These vibrations are then received by the nerves and converted to electrical nerve impulses, the ones sent to the brain. In the brain, these nerve impulses are analyzed and interpreted .