PhysicsWavesClass 11Class 12

Doppler effect in sound & sonic boom: interactive simulation

The Doppler Effect is the apparent change in frequency or pitch of a wave perceived by an observer moving relative to the wave source.

Useful for: NEET, JEE Main

Try this

When an ambulance approaches a stationary observer, the sound wavefronts are crowded together, resulting in a shorter apparent wavelength and higher pitch. As it moves away, the wavefronts spread out, causing a lower pitch.

  1. 1

    Turn on "Sound Pitch Audio" and listen to the siren as the ambulance passes.

    What you should see

    Hear the pitch drop sharply from high-frequency (approaching) to low-frequency (receding) at the exact instant the vehicle passes the observer!

  2. 2

    Set Source Speed vs to 340 m/s (Sound Speed).

    What you should see

    Wavefronts pile up directly at the front of the source, forming a constructive interference shockwave — a Sonic Boom (Mach 1.0)!

Formulas behind it

General Doppler Equation

f′=f0(v±vov∓vs)f' = f_0 \left(\frac{v \pm v_o}{v \mp v_s}\right)

Source Approaching Stationary Observer

f′=f0(vv−vs)>f0f' = f_0 \left(\frac{v}{v - v_s}\right) > f_0

Source Receding from Stationary Observer

f′′=f0(vv+vs)<f0f'' = f_0 \left(\frac{v}{v + v_s}\right) < f_0

Mach Number

M=vsvM = \frac{v_s}{v}

Common mistakes

  • Confusing source motion with observer motion. Moving source changes the apparent WAVELENGTH; moving observer changes the relative wave speed.
  • Assuming sound velocity in air changes with source speed. Wave speed in air is CONSTANT (340 m/s), regardless of vehicle speed.
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FAQ

Does Doppler Effect apply to light waves?

Yes! When stars move away from Earth, their light shifts to longer wavelengths (Redshift). When moving towards Earth, light shifts to shorter wavelengths (Blueshift).

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