Principles of the Physical World: Senior Cycle Physics · 5th Year

Active learning ideas

Light Spreading Out and Mixing

Active learning lets students see light’s wave behavior directly through hands-on experiments. When they manipulate pinholes, slits, and colored lights, the abstract concepts of diffraction and additive color become concrete and memorable.

• NCCA Curriculum Specifications
• NCCA: Primary Curriculum - Science - Energy and Forces

• 20–40 min
• Pairs → Whole Class
• 4 activities

Activity 01

• Experiential Learning
• 35 min · Pairs

Pairs: Pinhole Diffraction Setup

Pairs tape aluminum foil over a cardboard tube and puncture tiny holes of varying sizes. Shine a laser pointer through each hole onto a wall in a dark room. Measure and sketch the spreading pattern diameters, noting how smaller holes increase spread. Record slit width versus pattern size in a data table.

What happens to light when it shines through a tiny hole?

Facilitation Tip

During Pinhole Diffraction Setup, remind students to keep the laser and screen distances consistent so they can compare results across trials.

What to look for

Provide students with a diagram showing a single light source shining through two different sized pinholes onto a screen. Ask them to: 1. Sketch the pattern observed for each pinhole. 2. Explain why the patterns differ based on the pinhole size.

• Apply
• Analyze
• Evaluate
• Self-Awareness
• Self-Management
• Social Awareness

Activity 02

• Experiential Learning
• 40 min · Small Groups

Small Groups: LED Color Mixing Board

Provide red, green, and blue LED flashlights. Groups shine overlapping beams on a white poster board and predict colors like red plus blue for magenta. Photograph results and label primary, secondary combinations. Discuss why mixtures differ from paint.

What happens when you shine a red light and a blue light together?

Facilitation Tip

For LED Color Mixing Board, have students test each color alone first before combining pairs to build a clear understanding of additive mixing.

What to look for

In small groups, have students use colored LED torches (red and blue) to create magenta light. Ask them to record their observations and then answer: 'What happens to the light waves when red and blue light overlap?'

• Apply
• Analyze
• Evaluate
• Self-Awareness
• Self-Management
• Social Awareness

Activity 03

• Experiential Learning
• 25 min · Whole Class

Whole Class: Hair as Diffraction Grating

Dim lights and project a laser beam through a single classmate's hair held taut across the path. Observe twin bright spots flanking the main beam on a screen. Measure spot separation and repeat with different hair thicknesses. Class shares predictions on bending.

Can light bend around corners?

Facilitation Tip

When using Hair as Diffraction Grating, encourage students to hold the hair taut to create even spacing for clearer fringe patterns.

What to look for

Pose the question: 'Can light bend around corners?' Facilitate a class discussion where students use the concept of diffraction to explain why shadows have fuzzy edges and how this relates to light spreading out.

• Apply
• Analyze
• Evaluate
• Self-Awareness
• Self-Management
• Social Awareness

Activity 04

• Experiential Learning
• 20 min · Individual

Individual: Razor Edge Shadow Check

Each student uses a flashlight and straight razor blade to cast a shadow on paper. Examine the edge for fuzziness and sketch. Compare to geometric shadow prediction. Note diffraction evidence at the boundary.

What happens to light when it shines through a tiny hole?

Facilitation Tip

In Razor Edge Shadow Check, ask students to slowly move the razor closer to the screen to observe the gradual transition from sharp to fuzzy edges.

What to look for

Provide students with a diagram showing a single light source shining through two different sized pinholes onto a screen. Ask them to: 1. Sketch the pattern observed for each pinhole. 2. Explain why the patterns differ based on the pinhole size.

• Apply
• Analyze
• Evaluate
• Self-Awareness
• Self-Management
• Social Awareness

A few notes on teaching this unit

Teach this topic by letting students explore before formal explanation. Start with observations, then introduce terms like diffraction and interference only after they’ve seen the phenomena. Avoid lectures on wave theory upfront—let the experiments drive the concepts. Research shows that students retain wave behavior better when they measure and compare results rather than just observe demonstrations.

Students will describe how light spreads around edges and through small openings, explain why different pinhole sizes create different patterns, and predict color outcomes when mixing lights. They should connect these observations to wave interference and wavelength relationships.

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Watch Out for These Misconceptions

• During Pinhole Diffraction Setup, watch for students who assume larger pinholes always produce brighter patterns without considering spreading.

  Ask students to measure both the brightness and the spread of the pattern for each pinhole size, then compare the area of illumination to challenge their assumption.

• During LED Color Mixing Board, watch for students who think mixing all colors of light creates black like paint does.

  Have students test the combination of red, green, and blue lights first, then ask them to explain why their result differs from mixing paints before guiding them to the concept of additive color.

• During Hair as Diffraction Grating, watch for students who believe light passes straight through thin materials without bending.

  Have students measure the distance between fringes for different hair thicknesses and ask them to compare it to the wavelength of the laser light to show the relationship between gap size and bending.

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Methods used in this brief

• Experiential Learning