IP Physics Notes (Upper Secondary, Year 3-4): 7) Light

Study guide30 Sep 2025, 00:00 ZUpdated 30 Nov 2025

Master reflection and refraction laws, critical angle behaviour, and thin-lens constructions for IP optics questions.

Download PDF Join our Telegram study group

Q: What does IP Physics Notes (Upper Secondary, Year 3-4): 7) Light cover?
A: Master reflection and refraction laws, critical angle behaviour, and thin-lens constructions for IP optics questions.

Quick recap -- Light travels in straight lines until a boundary bends or reflects it. Track incident and refracted angles carefully and use lens rules to predict image position, size, and orientation.

The core idea is simple: Draw the normal first, then track how light reflects or bends.

Use it as a working check: Reflection keeps equal angles. Refraction bends because speed changes. Total internal reflection needs a higher-to-lower refractive index path and an angle above the critical angle.

Then go one layer deeper: Use the mirror, optical fibre, and lens rules to practise ray diagrams that show image position, size, orientation, and whether the image is real or virtual.

Keep your practice loop tight via our IP Physics tuition hub-it links each topic here to quizzes, diagnostics, and WA-style problem sets.

New to the Integrated Programme? Start with What is IP? | Browse all free IP notes.

These notes align with SEAB GCE O-Level Physics (6091) content used in IP programmes (exams from 2026).

Status: SEAB O-Level Physics 6091 syllabus (exams from 2026) checked 2025-11-30 - scope unchanged; remains the reference for these notes.

Reflection Basics

Reflection: bouncing of light from a surface.
Law 1: incident ray, reflected ray, and normal all lie in the same plane.
Law 2: angle of incidence equals angle of reflection, $i = r$ .
Smooth surfaces give specular reflection; rough surfaces scatter light, producing diffuse reflection.

Reviewed by

Chee Wei Jie·Academic Advisor (Physics)

Step	What to draw	Why it works
1	Mark the image the same perpendicular distance behind the mirror as the object is in front.	A plane mirror image is virtual and appears behind the mirror.
2	Draw a dashed straight line from the image to the eye.	This is the apparent path that the eye traces backwards.
3	Mark where that dashed line meets the mirror.	That point is where the real reflected ray must leave the mirror.
4	Join the object to that point on the mirror, then join that point to the eye.	The real light path now satisfies equal angles at the mirror.

Boundary clue	Speed change	Bend direction	What to check next
Lower refractive index to higher refractive index	Light slows down.	Towards the normal.	Refracted angle is smaller than incident angle.
Higher refractive index to lower refractive index	Light speeds up.	Away from the normal.	Refracted angle is larger than incident angle.
Higher to lower refractive index, with large incidence angle	Refraction may fail.	Ray reflects internally.	Compare the incidence angle with the critical angle.
Rectangular glass block with parallel faces	Slows on entry, speeds on exit.	Towards normal on entry, away on exit.	Emergent ray should be parallel to the incident ray, with lateral shift.

Object position	Image nature
Beyond $2f$	Real, inverted, diminished between $f$ and $2f$
At $2f$	Real, inverted, same size at $2f$
Between $f$ and $2f$	Real, inverted, magnified beyond $2f$
At $f$	Image at infinity
Inside $f$	Virtual, upright, magnified on same side

Calculation result	Diagram meaning	Final description to check
$v > 0$ for a converging lens	Rays actually meet on the far side of the lens.	Real image, usually inverted.
$v < 0$ for a converging lens	Rays diverge after the lens; their backward extensions meet on the object side.	Virtual image, upright, on the same side as the object.
$\lvert v \rvert > u$	Image distance is larger than object distance.	Magnified image.
$\lvert v \rvert < u$	Image distance is smaller than object distance.	Diminished image.

IP Physics Notes (Upper Secondary, Year 3-4): 7) Light

Reflection Basics

Plane Mirror Images

Plane mirror ray-path checkpoint

Refraction & Refractive Index

Refraction decision checkpoint

Apparent Depth & Lateral Shift

Total Internal Reflection (TIR)

Worked Example: Optical Fibre Core

Thin Lenses

Ray Construction Rules (Converging Lens)

Image Cases for Converging Lenses

Lens answer consistency checkpoint

Worked Example: Lens Imaging

Diverging Lens Notes

Practice Quiz

Key Takeaways

Related Posts