**Category:** Wave Physics  
**Subtype:** Interference of Waves  

**Problem Description:** This problem involves the interference of waves on the surface of a liquid, specifically focusing on two coherent sources (A and B) that are in phase. The problem provides the frequency of the waves, the distance between the sources, and the speed of wave propagation. It asks for the number of points on an ellipse (E) that experience maximum amplitude and are in opposite phase to a specific point (M) on the perpendicular bisector of the line segment AB.

**Key Elements:**
- **Find:** The number of points on the ellipse (E) with maximum amplitude that are in opposite phase to point M.
- **Given Data:** 
  - Frequency of waves: 10 Hz
  - Distance between sources A and B: 19 cm
  - Speed of wave propagation: 20 cm/s

This problem requires understanding wave interference patterns and the geometry of the ellipse formed by the two sources.