How does the Doppler effect cause a siren's pitch to increase as it approaches you? A. Sound waves are spread out, decreasing wavelength and increasing frequency. B. Sound waves are pushed closer together,decreasing wavelength and increasing frequency. C. Sound waves are pushed closer together,increasing wavelength and decreasing frequency. D. Sound waves are spread out, increasing wavelength and decreasing frequency.

## Step 1: Understanding the Doppler Effect<br />### The Doppler effect describes the change in frequency or wavelength of a wave in relation to an observer moving relative to the wave source.<br />## Step 2: Compression of Sound Waves<br />### As the siren approaches, the sound waves are compressed, meaning the wavelength decreases.<br />## Step 3: Relationship Between Wavelength and Frequency<br />### A decrease in wavelength results in an increase in frequency, since frequency and wavelength are inversely related.<br />## Step 4: Perception of Pitch<br />### The increase in frequency is perceived by the observer as an increase in pitch.