Understanding Types of Wave Fronts with Examples
A wavefront meaning is, it is the set or locus of all the points in the same phase. Here, the locus is the path travelled by a particular point emanating from the light source; however, there are millions of points like this. All these points undergoing locus form various types of wavefronts.
There are three types of wavefront, viz: plane wavefront, spherical wavefront, and cylindrical wavefront. Moving forward, we will understand these types with the wavefront Physics and Wavefront Lasik in detail.
More About Waves
In physics, periodic waves are used to describe the propagation of radiation energy of the light, sound, wind or any other kind of energy. And because this wave is a smooth periodic oscillation, it is described as a function of sinusoidal waves. In earlier times light was described as a combination of very tiny particles that do not have any mass. It was also theorised that the particles of different coloured lights were also different. All the other natural phenomena of light such as reflection, refraction, diffraction were understood based on this hypothesis and considering that light particles are elastic in nature.
In the 17th century, Christian Huygens made a groundbreaking scientific revolution. He proposed that light is actually a form of energy and moves in the form of waves. He explained it by suggesting that any point source of light radiates light waves in all directions simultaneously in three dimensions. The particles in its surrounding vibrate periodically under the influence of wave energy. In this type of propagation, the points of a particular location are present at the same phase with respect to time. The plane formed by this locus of points or particles in the same phase is known as a wavefront.
FAQs on Wave Front in Physics: Complete Guide
1. What is a wavefront in Physics?
In physics, a wavefront is defined as the locus, or set, of all points in a medium where waves from a source are in the same phase of oscillation. You can visualise it as a continuous surface that connects all the crests (or troughs) of a wave at a specific moment. For instance, the expanding ripples from a stone dropped in a pond form a series of circular wavefronts.
2. What are the main types of wavefronts based on the source shape?
The shape of a wavefront is determined by the shape of the light source. The three primary types covered in the CBSE syllabus are:
Spherical Wavefront: Generated by a point source of light, like a tiny LED or a candle flame. The wavefronts are concentric spheres that expand outwards from the source.
Cylindrical Wavefront: Produced by a linear or slit source of light. The wavefronts are coaxial cylinders that expand outwards.
Plane Wavefront: When a spherical or cylindrical wavefront is observed at a very large distance from its source, a small section of its curved surface can be considered flat. This is known as a plane wavefront. For example, the light reaching Earth from a distant star is treated as a plane wavefront.
3. How does Huygens' principle explain the propagation of a wavefront?
Huygens' principle is a fundamental concept that explains how a wavefront moves through a medium. It states that every point on a primary wavefront acts as a source of new secondary waves, known as wavelets. These wavelets spread out in the forward direction at the same speed as the original wave. The new position of the wavefront at a later time is simply the tangential surface that envelops all these secondary wavelets.
4. What is the relationship between a light ray and a wavefront?
A light ray and a wavefront are two complementary ways to describe the path of light. A light ray is an arrow indicating the direction of the wave's energy propagation. This ray is always drawn perpendicular to the wavefront at every point. For a spherical wavefront, the rays are radial lines pointing away from the centre. For a plane wavefront, the rays are a set of parallel lines, all perpendicular to the plane surfaces.
5. What is the difference between a spherical and a plane wavefront?
The key difference lies in their source and curvature. A spherical wavefront originates from a nearby point source and has a distinct curvature that decreases as it moves away from the source. In contrast, a plane wavefront is considered to have zero curvature. It originates from a source at an effectively infinite distance, which is why the wavefronts arrive as parallel planes.
6. Why is the concept of 'locus' important for understanding a wavefront?
The term 'locus' is critical because it emphasises that a wavefront is a continuous surface, not just a collection of a few points. It represents the *complete set* of all points that are vibrating in the same phase. For a point source in three dimensions, the locus of all points at an equal distance 'r' is a sphere. Since the wave travels at the same speed in all directions, all points on this sphere have the same phase, correctly forming a spherical wavefront. The idea of a locus mathematically defines the shape of the wavefront.
7. How would you draw the wavefront for light emerging from a convex lens when a point source is placed at its focus?
When a point source of light is placed at the principal focus of a convex lens, the lens refracts the diverging rays into a parallel beam. The light source produces spherical wavefronts that enter the lens. After passing through the lens, these spherical wavefronts are transformed into plane wavefronts, as the emergent rays are parallel to each other and perpendicular to the principal axis.
8. Is there a single formula to describe all wavefronts?
No, there isn't a single universal formula for a wavefront. The mathematical equation for a wavefront simply describes its geometric shape. For example:
A spherical wavefront with its origin at (0,0,0) is given by the equation x² + y² + z² = c²t², where 'c' is the wave speed and 't' is time.
A plane wavefront travelling along the x-axis is described by the simple equation x = constant.
Therefore, the specific equation or 'formula' changes depending entirely on the shape and orientation of the wavefront being described.
