From 5c2013f939923c67d6323d7eab64607ef23c947f Mon Sep 17 00:00:00 2001 From: eggy Date: Mon, 14 Dec 2020 11:53:17 -0500 Subject: [PATCH] phys: reflection and refraction --- docs/sph3u7.md | 42 +++++++++++++++++++++++++++++++++++++++++- 1 file changed, 41 insertions(+), 1 deletion(-) diff --git a/docs/sph3u7.md b/docs/sph3u7.md index b410cb6..761ab84 100644 --- a/docs/sph3u7.md +++ b/docs/sph3u7.md @@ -638,6 +638,46 @@ When waves of the same frequency meet, if their crests or troughs overlap, a **s ## 4.4 - Wave behaviour +### Reflection + +When waves meet a flat surface and are not diffused or refracted, they are reflected at the same angle they entered relative to the **normal**. + +!!! definition + - The **incident** wave/angle refers to the wave hitting the surface. + - The **reflected** wave/angle refers to the wave moving away from the surface. + - The **normal** is an imaginary line perpendicular to the surface at the arrival point of the incident ray. + +(Source: Kognity) + +### Refraction + +When light travels between two media that have different **optical densities**, it refracts and changes its direction as well as its speed. The **frequency** of the wave does not change but its speed does, therefore the **wavelength** changes as well. + +!!! definition + **Refraction** is the change in the direction and speed of light from a change in the optical density of the medium it travels through. + +When a ray travels from a **less** optically dense to **more** optically dense medium (fast to slow), the ray bends **toward** the normal and its wavelength decreases. + +(Source: Kognity) + +### Snell's law and total internal reflection + +The **refractive index** of a medium represents the ratio of wave speeds in the media, where $v$ is the speed of light in the medium: +$$n=\frac{c}{v}$$ + +Air has an index of refraction of $1$. + +Snell's law states that the incident and refracted angles are related by the index of refraction of the media. +$$\frac{n_1}{n_2}=\frac{\sin\theta_2}{\sin\theta_1}=\frac{v_2}{v_1}$$ + +or +$$n_1\sin\theta_1=n_2\sin\theta_2$$ + +If a ray travels from a **slower** to a **faster** medium, the ray bends away from the normal. If the ray would refract so much that it does not leave the incident medium at all, **total internal reflection** (TIR) occurs and the ray follows the rules of **reflection**. The critical angle denotes the incident angle required for the refracted angle to be exactly $90°$, and any angle greater than it results in TIR. +$$\sin\theta_c = \frac{n_2}{n_1}$$ + +(Source: Kognity) + ### Diffraction !!! definition @@ -655,7 +695,7 @@ As a wavefront passes an aperture, there are fewer points beside it and the wave For observable diffraction, the wavelength must be greater than or equal to the width of the aperture. -## 4.4 - Standing waves +## 4.5 - Standing waves A standing wave does not travel, so no energy is transferred. They are caused by the interference of symmetrical travelling waves moving in opposite directions.