The full archive.
Page 9 of 13 — articles on the physics of light, sorted newest first.
Converging vs Diverging Mirror: Is Concave Always Converging?
A converging mirror (concave) bends light inward to a focal point. A diverging mirror (convex) spreads light outward. Converging mirrors can form real images; diverging mirrors always form virtual ones. Here is why a concave mirror is always converging, a convex mirror is always diverging, and how to remember which is which.
Convex Mirror: Complete Guide to 5 Uses & Examples
A convex mirror is a curved mirror where the reflecting surface bulges outward like a dome. It diverges parallel light rays so they appear to come from a focal point behind the mirror. Because it always produces an upright, diminished image with a wider field of view, it is the standard for vehicle rearview mirrors, security mirrors, and traffic safety mirrors. Here is how convex mirrors work, their ray diagrams, image formation, mirror formula, and everyday uses.
How Does a Mirror Work? The Physics of Reflection in Mirrors
A mirror works by reflecting light at the same angle it arrives, following the law of reflection. A thin metal coating (silver or aluminium) behind a glass sheet absorbs and re-emits photons almost perfectly, creating a clear image. Here is how mirrors are made, how each type forms images, and why your reflection is flipped front-to-back, not left-to-right.
Plane Mirror: 5 Surprising Properties of Plane Mirror Images
A plane mirror is a flat reflective surface that forms a virtual, upright image the same size as the object. The image appears as far behind the mirror as the object is in front, and it is laterally inverted — left and right swap places. Unlike curved mirrors, plane mirrors never magnify, shrink, or distort the image. Here are the 5 properties of plane mirror images, how to draw their ray diagrams, and where they are used every day.
Real vs Virtual Image: 7 Clear Differences (Complete Guide)
A real image forms when light rays actually converge at a point — you can project it on a screen. A virtual image forms where light rays only appear to diverge from a point — you cannot capture it on a screen. Real images are inverted; virtual images are upright. Concave mirrors and converging lenses can produce both types; plane mirrors, convex mirrors, and diverging lenses produce only virtual images. Here are the 7 key differences between real and virtual images, with examples from every common optical device.
Critical Angle Formula & How to Calculate It (Worked Examples)
The critical angle formula θc = sin⁻¹(n₂/n₁) gives the angle of incidence at which light switches from refraction to total internal reflection. Here is how to derive it from Snell's law, use it step by step, and apply it with 6 worked examples for different materials.
Critical Angle & Reflection: The Relationship Explained
The critical angle of reflection is the threshold angle of incidence in a denser medium where light goes from partial reflection (some transmits, some reflects) to total internal reflection (100% reflects). Below θc you get a mix of refraction and reflection. At exactly θc the refracted ray grazes the boundary and reflection is minimal. Beyond θc all light reflects. Here is how this relationship works and why it matters.
Critical Angle: Simple Definition, Formula & 4 Worked Examples
The critical angle is the angle of incidence in a denser medium at which the refracted ray in the rarer medium runs exactly along the boundary at 90 degrees. Any angle larger than this produces total internal reflection. Here is the formula, how to calculate it, and 4 worked examples for water, glass, diamond, and ice.
FTIR Explained — Frustrated Total Internal Reflection Guide
Frustrated total internal reflection (FTIR) is what happens when light that should reflect entirely instead tunnels across a tiny gap into a third medium. It spoils perfect TIR — and it is the physics behind fingerprint scanners, optical sensors, and a beautiful party trick with a glass of water.
TIRF Microscopy Explained: Total Internal Reflection Fluorescence Guide
Total internal reflection fluorescence (TIRF) microscopy is an optical technique that uses the evanescent wave generated by total internal reflection to selectively excite fluorophores within 100-200 nanometres of the coverslip surface. This produces images with extremely low background and high signal-to-noise ratio, ideal for studying cell membrane dynamics, endocytosis, exocytosis, and single-molecule events.
Total Internal Reflection Explained: Definition, Conditions & Real-World Examples
Total internal reflection (TIR) happens when light travelling through a denser medium hits the boundary with a rarer medium at an angle greater than the critical angle, and the light reflects entirely back into the denser medium. Here are the 3 conditions for TIR, the critical angle formula, and 5 real-world examples.
Concave Lens for Myopia: Complete Nearsighted Correction Guide
A concave lens corrects myopia by diverging light before it enters the eye, shifting the focal point back onto the retina. Myopia (nearsightedness) affects about 30% of people in the UK and US, and concave lenses are the standard treatment. Here is how they work, how to read your prescription, and what alternatives exist.