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Science lesson plan · 7th grade (Year 8 in England) · 45 minutes

Colour, prisms and refraction

Light, sound and waves

CCSS NGSS.MS-PS4-2England: KS3 Physics: Waves (light waves)England: KS4 Combined Science: Light and electromagnetic waves

Objective and success criteria

Students will: Colour, prisms and refraction.

  • 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: The electromagnetic spectrum; 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.
  1. A ray of light hits a flat mirror at an angle of incidence of 70° (measured from the normal). What is the angle of reflection? → 70 °Prompt: The law of reflection compares the two angles.
  2. A ray of light hits a mirror. The angle between the ray and the mirror surface is 50°. What is the angle of reflection (measured from the normal)? → 40 °Prompt: The normal is at 90° to the mirror.
  3. What is the "normal" in a ray diagram? (a line at 90° to the surface where the ray hits / the mirror itself / the reflected ray / any ordinary line) → a line at 90° to the surface where the ray hitsPrompt: Angles are measured from it.

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: Colour, prisms and refraction. 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: Why does a red apple look red in white light?
  • Step 1: Coloured objects reflect their own colour and absorb the rest.
  • Step 2: So the answer is: It reflects red light and absorbs the other colours
  • Answer: It reflects red light and absorbs the other colours
  • 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.
  1. What does a prism do to white light? (splits it into a spectrum of colours / makes it brighter / stops it completely / turns it black) → splits it into a spectrum of coloursPrompt: Think of a rainbow.
  2. Colour and light: which statement is NOT true? (Light travels at the same speed in glass as in air. / Light slows down when it enters glass or water. / White light is a mixture of colours. / Black objects absorb most of the light that falls on them.) → Light travels at the same speed in glass as in air.Prompt: Does a filter add colour or take colours away?

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 6 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.
  1. Colour and light: which statement is NOT true? (A red filter lets red light through and absorbs other colours. / White light is a mixture of colours. / White objects absorb all colours. / Light slows down when it enters glass or water.) → White objects absorb all colours.Prompt: Does a filter add colour or take colours away?
  2. Why does a red apple look red in white light? (It makes red light / It reflects all colours / It absorbs red light / It reflects red light and absorbs the other colours) → It reflects red light and absorbs the other coloursPrompt: We see the colours that bounce off an object.

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: The electromagnetic spectrum; 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-7.

Free lesson plan from eurekami.com/lesson-plan-builder

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Colour, prisms and refraction

Name

Date

Score/ 6

  1. Question 1

    What colour does a white T-shirt look under only red light?

    • A. green
    • B. red
    • C. blue
    • D. white

  2. Question 2

    Colour and light: which statement is NOT true?

    • A. A red filter lets red light through and absorbs other colours.
    • B. Black objects absorb most of the light that falls on them.
    • C. A red filter turns white light red by adding red.
    • D. White light is a mixture of colours.

  3. Question 3

    What does a prism do to white light?

    • A. stops it completely
    • B. makes it brighter
    • C. splits it into a spectrum of colours
    • D. turns it black

  4. Question 4

    Why does a red apple look red in white light?

    • A. It reflects red light and absorbs the other colours
    • B. It absorbs red light
    • C. It reflects all colours
    • D. It makes red light

  5. Question 5

    What colour does a green leaf look under only red light?

    • A. white
    • B. red
    • C. black (very dark)
    • D. green

  6. Question 6

    A pencil in a glass of water looks bent. Why?

    • A. The water bends the pencil
    • B. Light refracts (changes direction) as it passes from water to air
    • C. The glass is curved
    • D. Light reflects off the water

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Answer key: Colour, prisms and refraction

  1. 1. B. red

  2. 2. C. A red filter turns white light red by adding red.

  3. 3. C. splits it into a spectrum of colours

  4. 4. A. It reflects red light and absorbs the other colours

  5. 5. C. black (very dark)

  6. 6. B. Light refracts (changes direction) as it passes from water to air