Refraction and Lenses

Bending at a Boundary

refraction qualitatively

When light crosses from one medium into another, its ray can bend toward or away from the normal.

Example

When light crosses from one medium into another, its ray can bend toward or away from the normal. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

A boundary can bend a ray

When light crosses from one transparent material into another, the ray can change direction at the boundary. The normal is the reference line for saying which way it bends.

cross a boundary⇒ray may bend\text{cross a boundary} \Rightarrow \text{ray may bend}
A ray bends at a boundaryA ray crosses a boundary and bends closer to the normal.airglassnormal

This lesson makes no angle claim

The picture shows the idea of bending toward the normal, but it does not claim a numerical angle. The exact sine law is a deeper model than this first lens book needs.

qualitative bend only\text{qualitative bend only}
A ray bends at a boundaryA ray crosses a boundary and bends closer to the normal.airglassnormal

The honest claim is direction change

This page is still useful because it separates the visible fact from the later formula. The ray changes direction at the boundary; this first model does not assign a measured bend angle.

shown: bend directionnot shown: angle value\text{shown: bend direction}\qquad \text{not shown: angle value}
A ray bends at a boundaryA ray crosses a boundary and bends closer to the normal.airglassnormal
optics This lesson is qualitative. Snell's law uses sine values, so exact angle arithmetic is out of scope here.