Science lesson plan · 6th grade (Year 7 in England) · 45 minutes
The law of reflection: calculate angles
Light, sound and waves
CCSS NGSS.MS-PS4-2England: KS3 Physics: Waves (light)
Objective and success criteria
Students will: The law of reflection: calculate angles.
- I can answer questions on today's skill on my own, without help.
- I can explain each step and say why it works.
- I can check my answer and spot a mistake.
Before and after
Needs first: Reflection of light
Leads to: Refraction: refractive index, Snell's law and critical angle
Materials: Slinky or rope, Mirrors and torches, Mini whiteboards, A diagram or short video clip of the idea, Printed student sheet (below).
Warm-up · 5 min
- Quick retrieval from earlier learning (Reflection of light). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- A ray of light hits a flat mirror at an angle of incidence of 45° (measured from the normal). What is the angle of reflection? → 45 °Prompt: The law of reflection compares the two angles.
- A ray of light hits a mirror. The angle between the ray and the mirror surface is 70°. What is the angle of reflection (measured from the normal)? → 20 °Prompt: The normal is at 90° to the mirror.
- How does a periscope let you see over a wall? (It makes its own light / It bends light with magnets / Two mirrors reflect light down to your eyes / Light goes through the wall) → Two mirrors reflect light down to your eyesPrompt: Light travels in straight lines, so it must be redirected.
Hook · 5 min
- Ask the class to make a wave with a rope or slinky and describe what moves and what doesn't.
- Share the objective: The law of reflection: calculate angles. Read the success criteria together.
I do: model it · 10 min
- Work through the example out loud, saying why you do each step, not just what you do.
- Example: A ray of light hits a flat mirror with an angle of incidence of 35°. What is the angle of reflection, in degrees?
- Step 1: angle of incidence = angle of reflection
- Step 2: So the answer is: 35 °
- Answer: 35 °
- Pause after each step and ask a student to say what comes next.
We do: guided practice · 10 min
- Do these together. Students try each step on whiteboards before you reveal it.
- Use the hints as prompts rather than giving the answer.
- A ray of light hits a flat mirror with an angle of incidence of 70°. What is the angle of reflection, in degrees? → 70 °Prompt: Both angles are measured from the normal.
- A ray of light makes an angle of 20° with the surface of a mirror. What is the angle between the incident ray and the reflected ray, in degrees? → 140 °Prompt: Angles are measured from the normal, which is at 90° to the mirror.
You do: independent practice · 10 min
- Students work on the student sheet. Circulate and check the first two answers of every student early.
- Students who finish: write a question of their own for a partner, with the answer.
The 8 questions are on the student sheet below, with answers in the key.
Exit ticket · 5 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- What is "the normal" in a ray diagram? (the mirror itself / the reflected ray / a line at 90° to the mirror where the ray hits / any line parallel to the mirror) → a line at 90° to the mirror where the ray hitsPrompt: It is usually drawn as a dashed line.
- A ray of light makes an angle of 75° with the surface of a mirror. What is the angle between the incident ray and the reflected ray, in degrees? → 30 °Prompt: Angles are measured from the normal, which is at 90° to the mirror.
Watch out for
- Everyday meanings of words getting in the way of the science meaning: define key words explicitly.
- Remembering facts without the reason: ask "why?" and "what is the evidence?"
Support and stretch
Support
- Review first: Reflection of light.
- Use concrete materials: slinky or rope.
- Give the first step of each question, or a partly worked example to finish.
- Pair with a confident partner for the guided practice.
Stretch
- Move on to: Refraction: refractive index, Snell's law and critical angle.
- Explain a common mistake in writing and how to fix it.
- Write a word problem that uses today's skill, then solve a partner's.
Homework and more practice
Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-6.
Free lesson plan from eurekami.com/lesson-plan-builder