The Doppler Effect - AP Physics 2

Observed wavelength. The wavelength measured by the observer after Doppler shifting.

Pitch is higher when approaching. Approaching vehicles create higher pitch, receding vehicles create lower pitch.

$\Delta \lambda = \lambda_o \frac{v}{c}$. For light, the shift is proportional to velocity divided by light speed.

Speed of sound in the medium. This constant depends on the medium's properties and temperature.

Observed frequency $f' = 377$ Hz. Source moving away from stationary observer: $f' = 400 \times \frac{340}{360} = 377$ Hz.

Blueshift. Shorter wavelengths appear bluer, indicating approach toward the observer.

Speed of the observer. Positive when observer moves toward source, negative when moving away.

Measures star velocities. Spectral line shifts reveal whether stars are approaching or receding.

Yes, for electromagnetic waves. Light waves don't need a medium, so the effect still occurs in space.

Speed of sound in the medium. This constant depends on the medium's properties and temperature.

Yes, for electromagnetic waves. Light waves don't need a medium, so the effect still occurs in space.

Frequency decreases. Receding motion stretches wavefronts, creating lower frequency.

Speed radar guns. Police use Doppler radar to measure vehicle speeds for traffic enforcement.

Observed frequency equals source frequency. No relative motion means no change in wavefront spacing or frequency.

Speed of light in vacuum. The universal constant approximately $3.0 \times 10^8$ m/s.

No effect on frequency. Equal and opposite velocities cancel out, producing no net Doppler shift.

$f' = f \frac{v + v_o}{v + v_s}$. Observer velocity is positive when moving toward source, source velocity positive when moving toward observer.

Speed of the source. Positive when source moves toward observer, negative when moving away.

Wavelength decreases. Higher frequency corresponds to shorter wavelength in electromagnetic waves.

Wavefronts moving relative to an observer. Relative motion changes the spacing between successive wavefronts.

Observed frequency $f' = 515$ Hz. Observer moving toward stationary source: $f' = 500 \times \frac{350}{340} = 515$ Hz.

Observed frequency. This is the frequency detected by the observer after the Doppler shift occurs.

Sound and light waves. The effect occurs for all wave phenomena including mechanical and electromagnetic waves.

Frequency increases. Observer motion toward source compresses received wavefronts.

Frequency decreases. Observer motion away from source stretches received wavefronts.

Detects motion of raindrops. Radar waves reflect off moving precipitation, showing velocity information.

Use observed frequency shift. Rearrange the Doppler formula to solve for unknown velocity.

Wavelength increases. Lower frequency corresponds to longer wavelength in electromagnetic waves.

Higher speed reduces effect. Higher wave speed in the denominator reduces the fractional frequency change.