Rayat Shikshan Sansthas Radhabai Kale Mahila Mahavidyalaya Ahmednagar

Rayat Shikshan Sanstha’s Radhabai Kale Mahila Mahavidyalaya, Ahmednagar Doppler Effect Represented By Prof. Kurkute P. V. DEPARTMENT OF PHYSICS

Doppler Effect

• Defination: The change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source.

Uses of Doppler effect Astronomy Doppler effect is used to measure the speed at which stars and galaxies are approaching or receding from us, in a mechanism named red shift or blue shift. Redshift happens when light seen coming from an object that is moving away is proportionally increased in wavelength, or shifted to the red end of the spectrum. Medical imaging In medicine, the Doppler Effect can be used to measure the direction and speed of blood flow in arteries and veins. Radar The Doppler effect is used to measure the velocity detected objects where a radar beam is fired at a moving target. For example, the police use radar to detect a speeding vehicle. Radio waves are fired using a radar gun at the moving vehicle. The velocity is calculated using the difference between the emitted frequency and the reflected frequency. In a similar way, Doppler radar is used by weather stations to calculate factors like wind speed and intensity.

Calculating the Frequency Change The formula for determining the frequency during this event is as follows: Math Equation ƒ = observed frequency c = speed of sound Vs = velocity of source (negative if it’s moving toward the observer) ƒ 0 = emitted frequency of source

Problem Suppose you are standing on the corner of 5 th Avenue and 34 th Street waiting for the light to change so you can cross the street. An approaching southbound ambulance is heading your way traveling at 35 miles per hour. If we know that the frequency of the ambulance siren is 700 Hz, we can calculate the frequency of what you hear: c, the speed of sound, is 340. 29 m/s Vs, the velocity of the source, is 35 mi/h, or 15. 6464 m/s ƒ 0, the frequency of the ambulance siren, is 700 Hz Therefore, ƒ ≈ 734 Hz