MYP Physics: Light, Reflection & Refraction FAQ

Light, reflection and refraction get assessed mainly through Criterion A (Knowing and Understanding) and Criterion C (Processing and Evaluating) — usually a lab investigating the law of reflection or Snell's law, plus exam questions on ray diagrams. Criterion D often appears too, if you're asked to evaluate a real-world optical device.

Reflection is light bouncing off a surface at the same angle it hit it — angle of incidence equals angle of reflection, always measured from the normal. Refraction is light bending as it passes into a different medium, because its speed changes. Same light, two completely different behaviours, and exam questions love mixing them up.

The law of reflection states the angle of incidence equals the angle of reflection, both measured from the normal (the line perpendicular to the surface at the point of contact). It applies to plane and curved mirrors alike and is the basis for every ray diagram you'll draw in this topic.

Refractive index (n) is calculated using Snell's Law: $n_1\sin {\theta }_1=n_2\sin {\theta }_2$, where θ₁ and θ₂ are angles from the normal in each medium. For a single medium against air, $n=\frac{c}{v}$, comparing the speed of light in a vacuum to its speed in that material.

Total internal reflection happens when light travelling from a denser to a less dense medium hits the boundary at an angle greater than the critical angle — instead of refracting out, it reflects entirely back inside. The critical angle is found using $\sin {\theta }_c=\frac{n_2}{n_1}$, where n₁ is the denser medium.

Lenses form images by refracting light rays as they pass through curved glass or plastic. A convex (converging) lens bends parallel rays inward to a focal point, producing real or magnified images depending on object distance. A concave (diverging) lens spreads rays outward, always producing a smaller, upright virtual image.

The biggest one: measuring angles from the surface instead of the normal on every reflection and refraction question. Second: forgetting light bends towards the normal entering a denser medium and away from it entering a less dense one. Third: mixing up real and virtual images when describing lens or mirror behaviour.

Top marks in MYP Sciences come from precise scientific language, accurate labelled diagrams, and genuine evaluation — not just correct answers. For this topic, that means quoting the law of reflection or Snell's Law by name, showing full working in calculations, and linking your findings back to a real optical application when asked to evaluate.

Expect a hands-on lab measuring angles of incidence and refraction as light passes through a glass or perspex block, then calculating refractive index from your data. Some schools instead use a ripple tank to show wave refraction, or a laser and mirror set-up for reflection — either way, you'll be assessed on accurate measurement and graphing.

MYP reflection and refraction feeds directly into the DP Physics wave phenomena topic, where you'll meet the same Snell's Law but add diffraction, polarisation and more rigorous treatment of lens and mirror equations. Getting comfortable with ray diagrams and refractive index now saves real time later.

Yes — light and optics concepts can appear in the on-screen MYP eAssessment for Sciences, typically as multiple-choice or short-response items testing ray diagrams, calculations and application questions. Most schools also set their own internal assessments on this unit well before the eAssessment period, usually in MYP 4 or early MYP 5.

You need three: the law of reflection (angle of incidence = angle of reflection), Snell's Law ($n_1\sin {\theta }_1=n_2\sin {\theta }_2$), and the critical angle formula ($\sin {\theta }_c=n_2/n_1$). Most MYP schools provide these on a formula sheet, but check with your teacher — some expect you to know them without prompts.

Light, reflection and refraction is usually one unit among several in the MYP Sciences course, contributing to whichever criteria (A-D) your child's school assesses within that unit — not a fixed percentage of the year grade. Because MYP grades are criteria-based rather than topic-weighted, a weak result here can be balanced by stronger work in other units across the year.

MYP treats light, reflection and refraction as a conceptual and lab-based introduction — ray diagrams, Snell's Law, critical angle — assessed through the four MYP criteria. DP Physics (in the Wave Phenomena topic) goes further with diffraction gratings, polarisation and more demanding mathematical treatment, assessed through Paper 1, 2 and 3 exam papers instead.

The most effective revision combines redrawing ray diagrams from memory, practising Snell's Law calculations with different medium pairs, and reviewing past lab write-ups against the actual assessment criteria your teacher used. On revisionprep.com, the MYP Physics Revision Notes and Topical Worksheets cover this unit with practice questions mapped to Criteria A-D.