{"id":297,"date":"2026-06-22T00:24:32","date_gmt":"2026-06-22T00:24:32","guid":{"rendered":"https:\/\/physicsfundamentalsinfo.com\/blog\/?p=297"},"modified":"2026-06-22T00:25:46","modified_gmt":"2026-06-22T00:25:46","slug":"reflection-and-refraction","status":"publish","type":"post","link":"https:\/\/physicsfundamentalsinfo.com\/blog\/waves\/reflection-and-refraction\/","title":{"rendered":"Reflection and Refraction of Light"},"content":{"rendered":"\n
Definition<\/div>

\n\nReflection and refraction are the two ways light changes direction at a boundary between materials: reflection is when light bounces back off a surface, while refraction is when light bends as it passes through into a new medium because its speed changes. The bending follows Snell’s law, n\u2081 sin \u03b8\u2081 = n\u2082 sin \u03b8\u2082.\n\n<\/p><\/div>\n

Drop a straw into a glass of water and it looks snapped in half. Glance in a shop window at night and your own face stares back. Two everyday illusions, two different physics \u2014 and between them they explain mirrors, lenses, rainbows, cameras, your spectacles and the fibre\u2011optic cable carrying this page to your screen.<\/p>\n

Both effects happen at the same place: the boundary where one material meets another. What the light does there \u2014 bounce or bend \u2014 comes down to one question. Does it stay where it is, or does it cross over?<\/p>\n

What Are Reflection and Refraction?<\/h2>\n

Start with the boundary. Light is travelling along happily, and it meets a surface \u2014 the face of a mirror, the top of a pond, the curve of a lens. Two things can happen, and usually both do at once.<\/p>\n

Reflection<\/strong> is the part of the light that bounces back. It never leaves the first medium; the surface simply turns it around. A mirror reflects almost all of it, which is why you see a sharp image. Refraction<\/strong> is the part that crosses into the new medium \u2014 and as it crosses, it bends, because its speed changes.<\/p>\n

So reflection is a bounce and refraction is a bend. The crucial distinction is whether the light stays put or passes through.<\/p>\n

\n\n\n<\/path><\/marker>\n<\/path><\/marker>\n<\/path><\/marker>\n<\/defs>\n<\/rect>\n<\/line>\n<\/line>\n<\/line>\n<\/line>\n<\/line>\n<\/path>\n<\/path>\n<\/path>\n<\/circle>\n\u03b8\u2081<\/text>\n\u03b8\u2081<\/text>\n\u03b8\u2082<\/text>\nNormal<\/text>\nIncident ray<\/text>\nReflected ray<\/text>\nRefracted ray<\/text>\nn\u2081 (air)<\/text>\nn\u2082 (glass), denser<\/text>\nn\u2082 > n\u2081<\/text>\n<\/svg>\n<\/div>\n

A single ray hitting a boundary splits into a reflected ray (\u03b8\u2081 = angle of reflection) and a refracted ray (\u03b8\u2082), which bends toward the normal when it enters the denser medium.<\/p>\n

Reflection vs Refraction at a Glance<\/h3>\n

Because these two are so often confused, here is the side\u2011by\u2011side. Notice that the deciding factor running down the table is always the same: does the light stay in one medium, or cross into another?<\/p>\n

\n\n\n\n\n\n\n\n\n\n\n\n
Property<\/th>\nReflection<\/th>\nRefraction<\/th>\n<\/tr>\n<\/thead>\n
What happens<\/strong><\/td>\nLight bounces back off the surface<\/td>\nLight passes into a new medium and changes direction<\/td>\n<\/tr>\n
Medium<\/strong><\/td>\nStays in the same medium<\/td>\nCrosses into a different medium<\/td>\n<\/tr>\n
Cause<\/strong><\/td>\nThe surface turns the wave around<\/td>\nThe light’s speed changes between the two media<\/td>\n<\/tr>\n
Key law<\/strong><\/td>\nAngle of incidence = angle of reflection (\u03b8\u1d62 = \u03b8\u1d63)<\/td>\nSnell’s law: n\u2081 sin \u03b8\u2081 = n\u2082 sin \u03b8\u2082<\/td>\n<\/tr>\n
Speed of light<\/strong><\/td>\nNo change<\/td>\nChanges (slower in the denser medium)<\/td>\n<\/tr>\n
Wavelength<\/strong><\/td>\nUnchanged<\/td>\nChanges (the frequency stays the same)<\/td>\n<\/tr>\n
Everyday example<\/strong><\/td>\nYour image in a mirror<\/td>\nA straw looking bent in water<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

The Laws of Reflection and Refraction<\/h2>\n

Two short rules govern everything above. Both are written in terms of angles measured from the normal<\/strong> \u2014 the imaginary line drawn at right angles to the surface where the ray strikes it.<\/p>\n

The Law of Reflection<\/h3>\n

The reflected ray leaves at the same angle it arrived. Simple, and exactly true for any smooth surface.<\/p>\n

\u03b8\u1d62 = \u03b8\u1d63<\/div>\n