Explain Doppler effect in sound. Derive the expression for the apparent frequency of sound when the source and listener are
i) approaching each other.
ii) moving away from each other.

Explanation

### Step-by-Step Solution for the Doppler Effect in Sound

#### Introduction to the Doppler Effect
The Doppler Effect refers to the change in frequency (or wavelength) of a wave in relation to an observer moving relative to the source of the wave. In sound, this effect is observed when a sound source moves towards or away from an observer, resulting in a perceived change in the frequency of the sound.

#### Derivation of Apparent Frequency

**1. Apparent Frequency when Source and Observer are Approaching Each Other:**
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