[Application] : Application of Waves

What comes into your mind when you hear the word wave???

Sea Waves ??

Waves formed in water when you drop a piece of stone in still water

Most of you would have thought of the above and have the physical interpretation of waves as either of the above two. Can you think any other form of wave? Can you think applications of waves in any other field?

Well you would be surprised to know that waves have a widespread applications in our daily life. The light we see is a wave, the sound we hear is a wave, every musical instruments works by waves . In fact waves have applications in almost every field of everyday life – from wireless communications to detecting overspeeding vehicles, from the music of guitar to laser – almost every aspect of our everyday life in some way involves wave.

So what is a wave??

Wave is a transfer of energy from one place to another by oscillation of particles about their mean position. Only energy gets transferred- particles remain on their same position.

Is the definition too technical??

Okay lets see an excerpt from book “What is a wave” by Einstein and Infeld:

“A bit of gossip starting in Washington reaches New York [by word of mouth]

very quickly, even though not a single individual who takes part in spreading it

travels between these two cities. There are two quite different motions involved,

that of the rumor, Washington to New York, and that of the persons

who spread the rumor. The wind, passing over a field of grain, sets up a wave

which spreads out across the whole field. Here again we must distinguish between

the motion of the wave and the motion of the separate plants, which undergo

only small oscillations… The particles constituting the medium perform

only small vibrations, but the whole motion is that of a progressive wave. The

essentially new thing here is that for the first time we consider the motion of

something which is not matter, but energy propagated through matter” .

So it is something like people standing in row and transferring bricks at a building site: they remain stationary they just transfer the bricks.

Depending on the method of propagation waves can be classified into two parts – mechanical waves and electromagnetic waves. The basic difference between the two waves is that mechanical waves requires a medium to travel while electromagnetic doesn’t  Light is a electromagnetic wave while sound is mechanical. That’s why you  can’t hear sound on moon ( if you go there with your friend). Before  seeing some applications of waves which we encounter in our life let us see some common terminology of the waves.

Wavelength: Wavelength is distance between the the two adjacent crest (top ) or trough(bottom).

Frequency: It is the number of waves emitted in a second.

Doppler effect

Have you ever noticed change in sound of a car while approaching you and while receding. Ever thought of why this happens. Ever wondered how do astronomers found out that the universe is expanding? This is due to change in the frequency of sound when either the source or the observer is in motion while sound travels. Consider a situation in which you are moving towards a wave. It will take a little less time for a wavelength to reach you in comparison to if you were standing. Hence the frequency of the sound wave increases. Doppler effect has a very wide applications. It is used in radars, astronomy, medical, communications, military and various other purposes. Lets see some of these briefly.

• Radars (Speed Gun): With this, the velocity of an object can be calculated. This is commonly used by traffic police to detect overspeeding vehicles and in aviation sector to calculate the velocity of planes. A radar beam is projected at the vehicle and the reflected wave is detected and with measuring the time interval between successive waves and its frequency,its velocity is calculated. So next time if you are caught by traffic police on overspeeding just remind that its waves which let you caught.

• Astronomy: Doppler effect has immense importance in astronomy. With doppler effect you can find the (radial) velocity of the galaxies and can find out the binary stars!!! How? Astronomers calculate the change in frequency of light coming from a particular galaxy or star and measure the difference in frequency in comparison to the frequency if the particular object was stationary. (This they predict by spectral lines of radiation emitted elements of the core of star- they are not continuous but discrete and any change in frequency from incoming light should reflect that that particular star or galaxy is in motion. Technically it is termed as redshift and  blueshift (blue has higher frequency so an object approaching us will show blue shift (increase in frequency) and vice versa. On similar principles the temperature of a plasma can be measured by the red or blue shift
• Healthcare: Doppler effect has extensive applications in healthcare like echocardiogram which measures the blood flow velocity and show any anomaly or internal bleeding.

(Un)application:  Sonic boom and Shock waves:

Shock waves are created when an object travels faster than sound (supersonic speed). These are common by jet planes and are quite damaging breaking window panes of buildings, etc. As the plane emitting sound is moving faster than the speed of sound, the whole energy gets concentrated and when it strikes the ground it has devastating effects on buildings and trees. This can be more understood by the picture below.

An image of sonic boom created by a plane

Apart from doppler effect  waves have many other extensive applications also like the whole music is based on waves, light is also considered as waves, telecommunications is based on waves. Perhaps we’ll some more applications in future articles.