IB Physics: Wavefronts and Rays in Wave Models | IB物理：波动模型中的波前与光线

📚 IB Physics: Wavefronts and Rays in Wave Models | IB物理：波动模型中的波前与光线

In wave mechanics, two geometrical tools are extremely useful: wavefronts and rays. They allow us to describe the direction, speed and bending of waves without solving the detailed motion of every particle.

在波动力学中，两个几何工具极为有用：波前与光线。它们使我们能够描述波的方向、速度和弯折，而不必求解每个粒子的细致运动。

This article follows the IB Physics syllabus for Topic 4, especially the characteristics of wavefronts in plane, spherical and refracted waves. You will learn how to draw and interpret wave diagrams, and where the ray model fails.

本文依照IB物理教学大纲Topic 4的要求，重点讨论平面波、球面波和折射波中波前的特征。你将学会绘制和解读波动图，并理解光线模型在何时失效。

1. What Is a Wavefront? | 什么是波前？

A wavefront is an imaginary line or surface connecting points that oscillate in phase. At any instant, every point on a wavefront has the same displacement and is moving in the same direction with the same speed.

波前是一条假想的线或面，连接所有同相振动的点。在任一瞬时，波前上的每个点都具有相同的位移，并且以相同速度朝同一方向运动。

For water waves seen from above, a line connecting the crests is a wavefront; a line connecting the troughs is also a wavefront. In many diagrams, solid lines show crests and dashed lines show troughs.

从上方观察水面波时，连接各波峰的是波前；连接各波谷的也是波前。在许多图中，实线表示波峰，虚线表示波谷。

The perpendicular separation between two adjacent wavefronts is one wavelength (λ). If the wave is travelling in a constant medium, the wavefront spacing remains uniform.

相邻两条波前之间的垂直距离为一个波长（λ）。当波在均匀介质中传播时，波前间距保持均匀。

2. Rays: Direction of Energy Flow | 光线：能量传播的方向

A ray is a line drawn perpendicular to the wavefront, pointing in the direction in which the wave carries energy. In a uniform medium, rays are straight lines.

光线是一条垂直于波前、指向波传播能量方向的直线。在均匀介质中，光线为直线。

Rays are not physical objects; they are geometric constructions. If the wavefront is flat, the rays are parallel. If the wavefront is curved, the rays spread out or converge.

光线并不是真实物体，而是一种几何构造。如果波前是平面，光线相互平行；如果波前是曲面，光线则发散或会聚。

In ray diagrams for lenses and mirrors, arrows are used to show the direction of travel. These arrows are the same rays used in the wave model.

在透镜和面镜的光线图中，箭头表示传播方向。这些箭头正是波动模型中所使用的光线。

3. Plane Waves and Parallel Rays | 平面波与平行光线

A plane wave has flat, parallel wavefronts. At a large distance from a small source, spherical wavefronts are so slightly curved that they can be approximated as plane wavefronts.

平面波具有平坦且相互平行的波前。当距小波源很远时，球面波前弯曲极微弱，可近似看作平面波前。

Because the wavefronts are flat, all rays are parallel to one another. This represents a wave travelling in a single direction without spreading.

由于波前平坦，所有光线都彼此平行。这表示波沿单一方向传播而不发生扩展。

In a diagram, a plane wave is shown as a set of equally spaced parallel lines, with a few perpendicular arrows to indicate the rays.

在图中，平面波用一组等间距的平行线表示，并画几条垂直箭头代表光线。

4. Spherical Waves and Diverging Rays | 球面波与发散光线

A point source in a three-dimensional medium emits spherical wavefronts. If the wave is confined to two dimensions, for example ripples on water, the wavefronts are circular.

三维介质中的点波源会发出球面波前。如果波被限制在二维空间，例如水面波纹，则波前呈圆形。

For spherical waves, rays radiate outward from the source, perpendicular to each spherical surface. This is why a small light bulb

Published by TutorHao | IB Physics Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）