Doppler Effect, Waves and Noise Pollution

If the medium travels to the direction of a sound wave then a frequency of sound increases and if medium travels in opposite direction of a sound wave then the frequency of sound decreases. This note provides us an information on doppler effect waves and noise pollution.

Summary

Things to Remember

If the medium travels to the direction of a sound wave then a frequency of sound increases and if medium travels in opposite direction of a sound wave then the frequency of sound decreases.

When a star recedes from the earth, its spectral lines are displaced towards the red end which indicates an increase in wavelength and is called a red shift.

When a star approaches the earth, the spectral lines are displaced towards the violet and there is a decrease in wavelength, the velocity known as blue shifts.

The sound waves having a frequency between 20 Hz and 20, 000 Hz are known as sound waves which are an audible range of frequency.

The waves of frequency less than 20 Hz are known as infrasonic waves.

The sound of loudness greater than 45 Db is harmful to human ear which produce noise pollution.

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Subjective Questions

Q1:

State the Overcoming barriers to effective communication.

Type: Long Difficulty: Easy

Show/Hide Answer

Answer: <h4>Overcoming barriers to effective communication</h4>
Following are some of the points which should be taken into consideration for making the communication effective :
<ol>
<li>Planning before communication</li>
</ol>
The communicator must consider the goals and purpose of the receivers. The ideas to be transmitted must be well identified by collecting the facts and analyzing them before delivery.
<ol start="2">
<li>Be clear in purpose of communication</li>
</ol>
The sender must know what he or she wants to communicate, which could be either giving information or obtaining information. Clarity in purpose will help in encoding the message and choosing the proper mode of transmission.
<ol start="3">
<li>Give clear and complete message</li>
</ol>
The message to be communicated must be clear and complete so that the receiver could easily understand what the sender is trying to say. The unclear and incomplete message may result in misunderstanding.
<ol start="4">
<li>Speaking through eyes</li>
</ol>
The very 1st thing that a good speaker does is 1st looks at the audience and take a pause before conveying a message or delivering a speech. This helps to create a good impression on the audience. It is very important to maintain eye contact while communicating because if we don't maintain eye contact the other person may feel like he or she being ignored and it's quite likely that they will also try to ignore our message.
<ol start="5">
<li>Voice level</li>
</ol>
The speed with which the word are thrown must be such that audience can keep pace with them and are able to understand him. A thing that unknowingly happens with most of us is that we keep on repeating the filler words like I mean, you see, ah , etc this may certainly distract the audience.
<ol start="6">
<li>Facial expression</li>
</ol>
The face is the mirror of an individual's personality. Facial expression reveals what thought are running through a person's mind.All the emotions and various type of human behavior bring different expression on a face.
<ol start="7">
<li>Follow proper mode of transmission</li>
</ol>
The sender must be clear about the intent of the message and should choose the appropriate mode of transmission. Selection of medium depends on the subject matter, urgency of communication and situation.
<ol start="8">
<li>Deliver message in proper time</li>
</ol>
The proper timing should be decided by the sender. The message should be delivered promptly to all concerned personnel when it is required.
<ol start="9">
<li>Always be empathetic with the receivers and consider the emotion of others</li>
</ol>
To make the receiver more responsive to the communication, their needs and interests should be taken into accounts then they will be more responsive to communication.
<ol start="10">
<li>
<h4>Always ask for feedback</h4>
</li>
</ol>
Feedback should be always encouraged and respected. Only by a feedback system , we can check the receiver have understood the message as intended and their reactions to messages- their acceptance, suggestion on it.
<h4>Interpersonal communication</h4>
Interpersonal communication is the face to face exchange of information, message ,feeling , knowledge and personal beliefs between two or more persons. Interpersonal communication and relationship are designed to win the goodwill and cooperation of the people.
A nurse is in the core area to promote the relationship with a client, community, and other health personnel so an effective interpersonal relationship is most important for her daily life.
<ol>
<li>Interpersonal relationship with client</li>
</ol>
Clients are at the center of any health care services and nurses are around them to provide health service. A nurse is a core member of health team who is constantly in touch with physical, psychological, social and other problems faced by the patient in the hospital and in a community so the nurse should maintain a good interpersonal relationship in order to explore their problems and help to solve those problems.
<ol start="2">
<li>Interpersonal relationship with community</li>
</ol>
In a community, a nurses need to deal with various types of personnel like lay people ,teachers, leader, health personnel, literate people, illiterate people etc . The main role is to bring changes in their behavior. She has to deliver various health information for various people. For that IPR is a unique way. IPR is very essential for maintaining a good
public relationship. Likewise, it is also necessary to collect accurate data, identify their problems, plan health intervention, evaluate health care for the community.
<ol start="3">
<li>Interpersonal relationship with health personnel</li>
</ol>
A nurse is an important member of health team both in a hospital and in a community. She needs to maintain good IPR with other health members in order to have good teamwork. IPR enhances good cooperation, Harmony, and coordination among health members so that efficiency of their work is increased.
<h4>Techniques to improve IPR among members of health care team</h4>
<ol>
<li>Nurses should keep in mind that effective communication is the key to improving IPR.</li>
<li>Should respect all the health team members.</li>
<li>Have a positive attitude and respect other person's view as well.</li>
<li>Should be pleasant and considerate in her behavior.</li>
<li>Should be familiar with organization system and policy of an organization.</li>
<li>Should aware of her professional right.</li>
<li>Should have adequate number for efficient use knowledge and skills</li>
</ol>

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Doppler Effect, Waves and Noise Pollution

Effect of Medium

If the medium travels to the direction of sound wave then frequency of sound increases and if medium travels in opposite direction of sound wave then frequency of sound decreases. Apparent change in frequency, if direction of medium and sound wave is same, given by

\begin{align*} F’ &=\left [ \frac {(v + v_m) – u_0}{(v + v_m) –u_s} \right ] \times f \\ \end{align*}

Apparent change in frequency, if direction of medium and sound wave is opposite to each other. Then,

\begin{align*} F’ &=\left [ \frac {(v - v_m) – u_0}{(v - v_m) –u_s} \right ] \times f \\ \text {where,} \: v_m &= \text { velocity of medium} \\ v &= \text {velocity of sound} \\ u_o &= \text {velocity of observer} \\ u_s &= \text {velocity of source} \\ f’ &= \text {change in frequency} \\ \end{align*}

Limitation of Doppler Effect

The Doppler’s principle can only be applied in the cases where the relative velocity between the source and observer is less than the velocity of sound.
This principle is not applicable if the source moves towards the observer with supersonic velocity.

Doppler’s Principle in Light

When a star recedes from the earth, its spectral lines are displaced towards the red end which indicates an increase in wavelength and is called a red shift. When a star approaches the earth, the spectral lines are displaced towards the violet and there is a decrease in wavelength, the velocity known as blue shifts. If λ is the wavelength of light emitted by the tar in the stationary position, λ’ be the wavelength when it is in motion, u_s is the velocity of approach of the star and c is the velocity of light, then

\begin{align*} \lambda ‘ &= \left ( \frac {c – u_s}{c} \right ) \lambda = \left ( 1 - \frac {u _s}{c} \right ) \lambda = \lambda - \frac {u_s}{c} \lambda \\ \text {or,} \: \frac {u_s}{c} \lambda &= \lambda - \lambda ‘ \\ \text {or,} \: u_s &= \frac {c(\lambda - \lambda ‘)}{\lambda } \\ \end{align*}

When λ and the shift (λ – λ’) are known, the velocity of star can be calculated. The measurement of red shift of light from galaxies suggests that the universe is expanding.

Application of Doppler Effect

Velocity of approaching or receding stars can be determined by using Doppler’s principle using the formula,
$$ u_s = \frac {c(\lambda - \lambda ‘ )} {\lambda } $$
Red Shift: it has been observed that some distant nebulae are moving away with a velocity greater than 20 × 10³ km/s and the spectral lines appear to shift towards the red end of the spectrum by 200 A^o. This gives the idea that universe is expanding.
In radar: microwaves emitted from a radar transmitter are sent out towards the target and after reflection from the target, these waves are picked up by the receiving the station of radar. If the aeroplane is approaching the observing station, there will be an increase in frequency or decrease in frequency or decrease in the wavelength of microwaves. But is the aeroplane is moving away from the observing station, there will be a decrease in frequency or increase in wavelength.
In SONAR (Sound Navigation and Ranging): Doppler’s principle is used in SONAR for the detection of submarine or group of fishes under water in the sea. The SONAR makes use of ultrasounds of frequencies more than 20 kHz and the reflected signals can be used for calculating the speed approaching or receding of submarines under water.

Range of Hearing

Normal human ears can hear only those waves whose frequency lies between 20 Hz and 20,000 Hz. The sound waves having a frequency between 20 Hz and 20, 000 Hz are known as sound waves which are an audible range of frequency. The waves having a frequency less than 20 Hz and greater than 20, 000 Hz cannot be heard by human ear.

Infrasonic and Ultrasonic Waves

Infrasonic Wave

The waves of frequency less than 20 Hz are known as infrasonic waves. These waves are not audible to a human ear. For example vibration of earth’s surface and a sound of animals like elephants, rhinoceros and whales etc.

Ultrasonic Wave

The waves of frequency greater than 20, 000 Hz are known as ultrasonic waves or ultrasound. It is not audible for the human ear. Example: sound produced by jet planes, bomb blasting etc. In the case of bat, wings of bat produce ultrasound which is transmitted towards the prey. It receives quickly and which position is the prey, so, the bat can easily catch the prey.

Uses of Ultrasound

For welding plastics
To diagnosis of human disease of human disease (Eg: cancer in stomach)
To check the development of unborn baby
To kill bacteria in the liquid
To find faults and cracks in metals
To determine the depth of a sea

Noise Pollution

The sound of loudness greater than 45 Db is harmful to human ear which produce noise pollution. According to WHO, the loudness of city must be balanced up to 45 Db.

Effects of Noise Pollution

It causes permanent deafness.
It causes a loss in heavy power.
It causes a headache, blood pressure etc.
It resists doing work properly.
It causes disease like neurosis, insomnia, and hypertension, behavioral and emotional stress.
It interferes with a speech of people.

Control of Noise Pollution

Generating awareness about the cause of pollution.
Designing and fabricating silencing devices in aircraft engines or any other machines.
Room walls should be covered with sound absorbers.
Workers exposed to noise should be given bear plugs.
It can be controlled by banning the air horn.
It can be controlled by running loudspeaker, radio and another music system at low volumes.

References

Manu Kumar Khatry, Manoj Kumar Thapa, Bhesha Raj Adhikari, Arjun Kumar Gautam, Parashu Ram Poudel. Principle of Physics. Kathmandu: Ayam publication PVT LTD, 2010.

S.K. Gautam, J.M. Pradhan. A text Book of Physics. Kathmandu: Surya Publication, 2003.

Lesson

Acoustic Phenomena

Subject

Physics

Grade

Grade 12

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