When the observer is at rest and the source moves with a supersonic speed, the resultant wave motion is a conical wave known as……………………wave.

Explanation

### Step-by-Step Solution:

1. **Understanding the Scenario**: The question states that the observer is at rest while the source of the wave is moving with a supersonic speed. This means that the source is traveling faster than the speed of sound.

2. **Identifying the Wave Type**: When a source moves faster than the speed of sound, it creates a unique wave pattern. This phenomenon is different from the usual Doppler effect where the source moves at subsonic speeds.

3. **Wave Compression and Expansion**: As the source moves, it compresses the waves in front of it and expands the waves behind it. This results in a conical shape of the wavefronts due to the high speed of the source.

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