Wavefront means

Options

A. All particles in it have same phase
B. All the particles have opposite phase of vibration
C. Few particles are in same phase , rest are in opposite phase
D. None of these

Answer

### Step-by-Step Solution:

1. **Definition of Wavefront**: A wavefront is defined as the locus of all points in a medium that are vibrating in the same phase at a given instant. This means that all points on the wavefront experience the same stage of the wave cycle (e.g., crest, trough).

2. **Understanding Locus**: The term "locus" refers to a set of points that satisfy a particular condition. In the context of wavefronts, it refers to the collection of points that are at the same distance from the source of disturbance and are oscillating in unison.

3. **Types of Wavefronts**:
- **Spherical Wavefront**: When the source of disturbance is a point source (like a light bulb), the wavefronts are spherical. This is because the waves propagate outward in all directions, forming a sphere around the source.
- **Cylindrical Wavefront**: When the source of disturbance is a line source (like a laser beam), the wavefronts are cylindrical. The waves propagate along the length of the line, creating a cylindrical shape.

4. **Characteristics of Wavefronts**:
- All points on a wavefront are in the same phase of vibration. This means that if one point is at its maximum displacement (crest), all other points on that wavefront are also at their maximum displacement at that instant.
- Wavefronts can be visualized as surfaces in space where the phase of the wave is constant.

5. **Conclusion**: Based on the definitions and characteristics, we can conclude that wavefronts represent surfaces where all points are vibrating in the same phase. Therefore, the correct answer to the question "Wavefront means" is that it is the locus of all points in the field of an optical disturbance having the same phase at a given instant.