Doppler Effect Firman

Doppler Effect

By Firman Biologi

Learning Outcomes

After this topic you should be able to :

1. Understand the doppler effect

2. Calculate and solve problems with formula of the doppler effect

3. ​Applications of the doppler effect in daily life

Some text here about the topic of discussion

Why it is important?

Please take look at the link video

​https://youtu.be/2FQ9VYExJfc

Some text here about the topic of discussion

The Acoustic Doppler Current Profiler is a SONAR-like device, which is used to measure the velocity of water over a wide range of depths using the Doppler effect of sound waves scattered back from the particles in the water column.

​Some text here about the topic of discussion.

The ADCP contains a piezoelectric transducer, which transmits or receives sound signals. ADCP works by transmitting a sound "ping" at a constant frequency (above the range of human senses) into the water. As sound waves move, they bounce off particles suspended in the moving water and are reflected back to the instrument.

​Some text here about the topic of discussion.

Due to the Doppler effect, the sound waves reflected back from the particles moving away from the ADCP have a slightly lowered frequency as they return. Particles moving towards the instrument send back higher frequency waves.

​Some text here about the topic of discussion.

ADCP uses this shift to calculate how fast the particles and surrounding water are moving. It works in the frequency range of 38KHz to several MHz. The device, called SONAR, which is used for profiling air currents, works on the same basic principle.

​Some text here about the topic of discussion.

What is the doppler effect?

What will happen if you hear the siren of an ambulance approaching to you?

the ppicth of the siren is high ; the picth is lower

What will happen when the siren of an ambulance away from you?

What is the doppler effect?

The change of FREQUENCY of sound waves due the relative motion between the source and observer

The part of waves

Remember it

Multiple Choice

Which wave has high frequency?

• A

• B

Multiple Choice

An ambulance is driving towards you as you stand on the sidewalk. What happens to the pitch of the siren as it comes towards you?

• It decreases

• It increases

Multiple Choice

What best describes the doppler effect?

• A change in frequency of a sound waves due to the relative motion between the source and an observer

• An apparent change in the amplitude of a sound wave due to the relative motion between the source and an observer.

• An apparent change in the waveleght of a sound wave due to the relative motion between the source and an observer.

• A change of sound pitch

The police car moves FORWARD, sound waves get closer togheter in front of the police car, so the FREQUENCY and picth of sound heard by man are HIGHER.

The sound waves spread out behind the police car, hence the FREQUENCY and picth of sound heard by woman are LOWER.

The Simple Formula of Doppler Effect

Variables for the Doppler Effect equation for sound

f = frequency perceived

f_o = original frequency given off by the source

v = velocity of sound

v_o = velocity of the observer (+ if going towards the source and - if going away from the source)

v_s = velocity of the source (- if going towards the source and + if going away from the source)

The Simple Formula of Doppler Effect

If the two object are getting closer, the perceived frequency should be higher.

• When using the equation, if the observer is going towards the source, v_o is positive and the perceived frequency increases.

• When using the equation, if the source is going towards the observer, v_s is negative and the perceived frequency increases.

The Simple Formula of Doppler Effect

If the two object are getting closer, the perceived frequency should be higher.

• When using the equation, if the observer is going towards the source, v_o is positive and the perceived frequency increases.

• When using the equation, if the source is going towards the observer, v_s is negative and the perceived frequency increases.

The Simple Formula of Doppler Effect

For example if the observer and source were both going towards each other, the top numerator would become (v + v_o) and the bottom denominator would become (v – v_s).  If either the observer or source were not moving, you add 0 or just leave that v_o or v_s out of the equation.

Question

The speed of sound is 340 m/s one day and the source whose actual frequency is 700 Hz is moving 20 m/s away from the observer who is not moving.  What is the perceived frequency of the sound by the observer?

Given : ​f_o = 700 Hz ; v = 340 m/s ; v_o = 0 ; v_s = 20 m/s ; f = ?

Equation : f = f_o ((v (+/-) v_o)/ (v (-/+) v_s)) source moving away and the observer not moving makes the equation:

f = f_o ((v / (v + v_s))

Work:

f =700 ((340 / (340 + 20))

f = 661 Hz

​

Subject | Subject

Some text here about the topic of discussion

Multiple Choice

A police car drives towards a jogger at 28 m/s as she runs in the direction of the police car at 2 m/s. What would the 700 Hz siren sound like to the jogger? (The speed of sound today is 343 m/s)

• 767 Hz

• 777 Hz

• 787 Hz

• 797 Hz

Applications of The Doppler Effect in Daily Life

Use in Flow Measurement

Instruments have been developed such as the acoustic Doppler velocimeter (ADV) and the laser Doppler velocimeter (LDV) they are used to calculate the velocities in fluid flow. The ADV emits ultrasonic acoustics and the LDV emits a light beam, to help calculate the Doppler shift in the wavelength of reflection from particles in motion with the flow.​

Some text here about the topic of discussion

Doctors can use an echocardiogram, with certain limitations, to produce a precise assessment of the velocity of cardiac tissues and blood and determine in which direction blood flows at any given point with the Doppler effect’s help. One of the drawbacks is not being able to assess the cardiac function and valve areas. Calculating the velocity of blood flow in the veins and arteries using the Doppler effect is an accurate tool to determine vascular issues such as stenosis

Use in Medicals

​

With the help of sonars, the military uses the Doppler effect to be able to determine the speed of their submarines. The son buoy generates stable frequencies that will experience a Doppler effect when they come in contact with any object in motion or the submarine. The velocity in which the object in motion is reseeding or approaching from the target object is recorded.

Use in Military​