Which of the following statements about wave is not correct? i. A wavefront is a line which contains all particles whose vibration are in phase. ii. The dir...

The incorrect statement about waves is iii. A wavefront is not a circle which is common to particles that are in the same state of disturbance. Rather, a wavefront is an imaginary surface that connects all points in space that are reached by a wave at the same time during its propagation. Hence, the correct answer is (e) ii and iii only. (i) A wavefront is a line that connects all particles in the medium that are vibrating in phase, meaning that their displacement from equilibrium is the same at any given moment in time. This means that they reach their maximum and minimum amplitudes at the same time. (ii) The direction of propagation of a wave is always perpendicular to the wavefront. This is because each point on the wavefront is at the same phase of vibration and so has the same displacement from equilibrium at any given moment in time. Therefore, the wavefront itself is a surface of constant phase, and the direction of propagation is the normal to this surface. (iii) As mentioned earlier, a wavefront is not a circle which is common to particles that are in the same state of disturbance. However, it can be a circle in the case of a spherical wave, which emanates from a point source and spreads out uniformly in all directions.