Refraction and Optical Illusions

Overview

In this fourth lesson of Light: Paths, Bends and Bounces, students apply their understanding that light travels in straight paths to investigate refraction. They observe how light appears to bend when it passes between materials, distinguish refraction from reflection, and communicate an evidence-based model of an optical effect.

Learning intentions

Students will:

• describe refraction as a change in the path of light when it passes between materials
• distinguish between reflection and refraction
• use observations and a ray model to explain an optical effect
• pose a question, make a prediction and collect evidence in a fair investigation
• improve a scientific explanation using peer feedback.

Success criteria

• I can describe refraction as a change in the path of light between materials.
• I can distinguish reflection from refraction.
• I can use a labelled ray model to explain an optical effect.
• I can improve my explanation using feedback that is clear, accurate and evidence-based.

Curriculum links

• Light — sources, straight-line travel, shadows, reflection and refraction.
• Science inquiry — posing investigable questions, making reasoned predictions, and identifying relationships.
• Science inquiry — planning and conducting safe, repeatable investigations with changed, measured and controlled variables.
• Science inquiry — using labelled models, tables and diagrams to represent patterns and findings, and communicating explanations for a specific audience.

Lesson structure (60 minutes)

1. 0–10 min · Hook and prediction. Teacher displays an optical illusion, then demonstrates placing a coin in an empty cup and slowly adding water until the coin becomes visible; open the hook and prediction slides and ask, “Did the light really travel around the object?” Students independently record a prediction and reason on the prediction-observation-explanation sheet, then share ideas with a partner before class discussion. Do not confirm the explanation yet.

2. 10–18 min · Build the concept. Teacher models a ray diagram showing light travelling from an object, changing direction at the air–water boundary, reflecting from a surface into the eye, and explains that refraction is not reflection; use the refraction teaching slides to compare a straight path, a reflected path and a refracted path. Students annotate a simple diagram and use the sentence frame: “I think this is ___ because light ___.”

3. 18–32 min · Investigate apparent bending. Teacher places pencils or spoons in water and provides cups, containers and torches, reminding students never to shine a torch into anyone’s eyes; pairs observe from different angles and complete the first investigation on the investigation recording sheet. Students record what appears to change, sketch the apparent path, and compare it with a straight-line model. They answer: “What changed at the boundary between materials?”

4. 32–40 min · Refractive-image challenge. Teacher demonstrates a disappearing coin or refractive image and prompts pairs to test one change, such as viewing angle, water level or object position; return to the challenge and question slides. Students make a brief prediction, conduct repeated observations, and add evidence to their prediction-observation-explanation table. Teacher conferences with groups, checking whether students are ready to explain rather than simply describe what they see.

5. 40–52 min · Design a light trick. Teacher explains that pairs will design a safe optical illusion using water, a mirror, a lens or another transparent material. Each pair chooses a question, plans a simple repeatable method, and creates a labelled ray sketch and explanation on the optical-illusion design page. Students test and revise their design, identifying the light source, materials, boundary, apparent path and whether reflection or refraction is involved. Encourage an oral recording or teacher scribing where writing is a barrier.

6. 52–60 min · Demonstrate and reflect. Teacher invites selected pairs to demonstrate their light trick and uses the sharing and peer-feedback slides to display the feedback criteria: “clear, accurate, evidence-based”. Students give one specific strength and one improvement suggestion, then revise one sentence or label on their model. Collect the worksheets and ask students to complete: “The light appeared to bend because …” and “Reflection differs from refraction because …”

Resources

• the complete refraction lesson deck
• the prediction-observation-explanation and design worksheet
• Coins, cups and water
• Pencils or spoons
• Clear containers and small torches
• Mirrors, plastic lenses and transparent materials
• Paper, pencils, rulers and coloured pencils
• Safety glasses, towels and trays for spills

Assessment

• Listen to predictions and discussion for misconceptions, especially the idea that light curves around an object.
• Check investigation tables, labelled ray models and explanations for correct use of boundary, reflection, refraction, ray and material.
• Use the design conference and peer feedback to identify readiness for the final task: students should support an explanation with an observation or repeated result.

Differentiation

• Support with live modelling, sequential photo instructions, vocabulary mats, labelled example diagrams, sentence starters and flexible pairs. Provide pre-cut materials and a drawing template for students who need reduced fine-motor or organisational demands.
• Offer large, high-contrast diagrams, short captions, audio directions and alternatives to copying definitions for dyslexic learners. Allow oral, video or teacher-scribed explanations.
• Use mixed-readiness grouping, while assigning roles such as equipment manager, observer, recorder and explainer so every student participates.
• Extension: investigate how changing the angle or material affects the apparent bend. Students propose a controlled test, identify the changed, measured and controlled variables, repeat trials, and explain the pattern using a ray model.