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The Doppler Effect

The “Doppler Effect” refers to the phenomenon that when there is relative motion between a wave source and an observer, the observer receives the frequency deviating from that of the wave source. This experiment uses supersonic wave to demonstrate the Doppler Effect. Apply supersonic wave of 40 kHz and use a rotational disk with spiral lines to simulate the moving wave source and the observer. A frequency counter detects the change in received frequency. The Doppler Effect is now widely used for observing the motion of celestial bodies and satellites in support of the theory. It is also employed broadly in radar, sonar, or biomedical testing applications such as measurement of blood flow rate.


Power Supply
To supply DC power to the motor. Rotational speed can be controlled by altering the current.
Infrared Detector &  8747 TimerWith the infrared detector the rotating speed can be precisely determined by timing a large number (100 revolutions) of spin and then calculate the frequency shift.

Rotating Disk
Consisted of two spirals (radius proportional to spinning angles). The impinged ultrasonic wave reflect by the curved surface.

Ultrasonic Emitter, Receiver
Connect the ultrasonic emitter to the functiongenerator. Adjust the frequency and amplitude of the ultrasonic wave by altering the waveform of function generator. Connect the receiver to the frequency counter to measure the received frequency.

To measure the amplitude of the signal.

To increase the amplitude of the signals.

Frequency Counter
Used for measuring frequency of the received signal.

Function Generator
Used to generate electrical waveforms. This experiment uses 40 kHz ultrasonic wave.


The Doppler Effect


Department of Physics (Digital Archive Project of NTU General Physics Laboratory)
National Taiwan University