Reflection & Refraction Of Light
Key idea: G3 Physics and O-Level light hub: reflection, refraction, mirror ray diagrams, total internal reflection and optical fibres.
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The core idea
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Learning objectives
- Describe wave generation by vibrating sources, ropes and springs
- Describe ripple-tank waves using wavefronts
- Explain that waves transfer energy
- Explain that wave energy transfer does not transfer matter
- Use amplitude, frequency and wavelength to describe wave motion
- Define and use wave speed and period and interpret wave graphs
- Recall and apply wave speed = frequency × wavelength
- Compare transverse and longitudinal waves and give examples
- Explain sound production by vibration and the need for a medium
- Describe sound using compressions and rarefactions
- Relate sound loudness to amplitude and pitch to frequency
- Explain reflected-sound echoes and use them to measure distance
- Explain ultrasound use in sonar and soft-tissue scanning
- Use the normal, angle of incidence and angle of reflection
- Apply the law of reflection in constructions, measurements and calculations
- Use the normal, angle of incidence and angle of refraction
- Apply sin i divided by sin r as a constant for a fixed pair of media
- Define refractive index as vacuum light speed divided by medium light speed
- Explain the critical angle
- Explain the conditions for total internal reflection
- Apply total internal reflection to optical fibres and state advantages
- Describe how a thin converging lens acts on a light beam
- Define the focal length of a converging lens
- Construct real and virtual image ray diagrams for a thin converging lens
- Describe lens images as real or virtual, magnified or diminished, and upright or inverted
Light is a transverse electromagnetic wave. Use this hub to build the ideas in order: reflection, refraction, refractive index, total internal reflection and optical fibres. Continue to converging lenses after this sequence.
Light is a major sub-topic of the Waves Hub.
Before you begin:
Follow this order:
- What is Light?
- Reflection & Mirror Diagrams
- Refraction & Snell’s Law
- Total Internal Reflection (TIR)
Visual checkpoint: use the Light & Lens Explorer after step 4 and explain every angle from the normal.
Lessons
Reflection
What is Light?
Nature of light and its properties.
Reflection
Laws of reflection and types of reflection.
Plane Mirror Diagrams
Step-by-step ray drawing for mirrors.
Refraction & TIR
Refraction
Bending of light and refractive index calculations.
Total Internal Reflection
Conditions for TIR and optical fiber applications.
Revision
Quick Reference
| Concept | Formula / Law | Key Detail |
|---|---|---|
| Reflection | i = r | Incidence = Reflection |
| Refraction | n = (sin i)/(sin r) | Snell’s Law (Air to Medium) |
| Wave Speed | n = c/v | c = 3 × 10⁸ m s⁻¹ |
| Critical Angle | n = 1/(sin c) | For a boundary from the medium to air |
Quick facts to remember
- Normal: An imaginary line perpendicular (90°) to the surface at the point of incidence.
- Refractive Index (n): A ratio showing how much light slows down in a medium.
- Total Internal Reflection: Occurs when light travels from a denser to a less dense medium and the angle of incidence is greater than the critical angle.
- Image in Plane Mirror: Virtual, upright, same size, and laterally inverted.
- Bending: Light bends towards the normal when entering a denser medium (slowing down).
Top Exam Traps
- Angles: Always measure angles (incidence, reflection, refraction) from the NORMAL, not the surface.
- Lateral Inversion: In a mirror, the image is flipped left-to-right (Laterally Inverted), not upside down.
- Frequency: When light refracts, its speed and wavelength change, but its frequency stays constant.
- TIR Conditions: TIR can happen only when light travels from a higher refractive index to a lower refractive index, with i > c.
- Virtual Image: You cannot capture a virtual image on a screen because the light rays do not actually meet there.
Continue with the next resource in this course.
Course and syllabus information
- Course
- SEC G3 Physics
- Edition
- SEC G3 Physics 2027