A CAROLINA ESSENTIALS INVESTIGATION

Wave-Particle Duality of Light Phenomena

Total Time

Physical Science

Grade Level

9-12 High School

Introduction

This teacher-led demonstration illustrates wave-particle duality of light. The activities can be completed in 15 minutes with minimal setup time and can serve as an anchoring phenomenon for investigations into quantum atomic theory. Many of the experiments performed by early scientists can be replicated fairly easily with today’s technology, giving students insight into both the nature and history of science.

As evidence that light is a wave, you will demonstrate polarization of light and Young’s double-slit experiment showing light interference patterns. A take on Einstein’s photoelectric effect experiment provides evidence of the particle nature of light. As students progress through the concept of quantum atomic theory, they can repeatedly return to the evidence they gather from the demonstrations of light phenomena to construct explanations and argue the validity of past and current theories.

Phenomenon

Observations of:

Polarization of white light and laser light
Diffraction of white light
Interference patterns of laser light
Photoelectric effect

Essential Question

What are the models explaining the behavior of electromagnetic radiation, and what experimental evidence lends support to each model?

Activity Objective

Collect and interpret evidence for models of light as a wave and as a particle.

Next Generation Science Standards* (NGSS)

HS-PS4-3. Evaluate the claims, evidence, and reasoning behind the idea that electromagnetic radiation can be described either by a wave model or a particle model, and that for some situations one model is more useful than the other.

SCIENCE & ENGINEERING PRACTICES

Engaging in Argument from Evidence

DISCIPLINARY CORE IDEA

PS4.B: Electromagnetic Radiation

CROSSCUTTING CONCEPTS

Systems and System Models

Materials Needed

Diffraction of white light

Interference patterns for laser light

Photoelectric effect

Recommended Safety

Do not point the laser at anyone, and do not look directly into the laser.

Teacher Prep and Disposal

Set up each demonstration prior to class. Copy or upload the student page to a class website. All materials can be reused.

Teacher Preparation and Tips

A. Polarization of white light and laser light (wave model)

Position the flashlight and screen so students can see the light from the flashlight on the screen. Allow students to sketch or summarize their observations.
Place one of the polarizing filters in front of the flashlight and allow students to record observations.
Place the second polarizing filter in front of the first and allow students to record observations.
Rotate the second polarizing filter 90° and allow students to record observations.
Continue rotating the polarizing filter 90° until it is back in the original starting position. At each rotation, allow students to record observations.
Repeat the process with the laser light. You will need 1 polarizing filter since laser light is coherent light.

B. Diffraction of white light (wave model)

Position the flashlight and screen so students can see the light from the flashlight on the screen. Allow students to sketch or summarize their observations.
Place the diffraction grating in front of the flashlight and allow students to observe and record their observations.

C. Interference patterns for laser light (wave model)

Position the laser light and screen so students can see the light from the laser on the screen. Allow students to sketch or summarize their observations.
Place the diffraction grating in front of the laser and allow students to observe and record their observations.

D. Photoelectric effect (particle model)

1. Attach the leads to the multimeter. The black lead goes in the bottom hole on the right side of the meter and the red lead goes in the hole directly above it. (The black-lead hole is labeled COM, and the red lead hole is labeled VΩmA.)

1. Turn the multimeter to 20 V in the DCV section of the multimeter (upper left quadrant). If a reading of 0.00 V is not showing, check the battery and replace it if needed. The battery compartment is on the lower back of the multimeter.
2. Attach a lead with 2 alligator clips to the red lead. Attach a second lead with 2 alligator clips to the black lead.
3. Attach one leg of the LED bulb to the free red alligator clip. Attach the other leg of the LED to the free black alligator clip. Make certain there is contact between the alligator clips and the legs of the LED.

1. The multimeter should still be reading 0.00 V. Shine the flashlight directly onto the top of the LED bulb. If the voltage is negative, switch the leads on the legs of the bulb.
2. To demonstrate, have the students observe the LED and voltage reading with:
  - No light shining
  - White light shining close and directly above the LED
  - The UV LED shining close and directly above the LED
  - The red laser light shining close and directly above the LED

The LED will never “turn on” but there will be voltage readings.

Data and Observations

A. Polarization of white light and laser light (wave model)

For the white light—as you add the second polarizing filter and rotate it, the light will darken when the filters are at 90° of each other.
For the laser light—as you rotate the filter, the light will darken when the filter is at 90° to the plane of the light coming from the laser.

B. Diffraction of white light (wave model)

C. Interference patterns for laser light (wave model)

D. Photoelectric effect (particle model)

Students will record the voltage generated by white light, red laser light, and UV light.

Analysis and Discussion

Use your evidence to explain the model or theory of light that each phenomenon supports

See above.

Use your observations to explain the need for a theory of wave-particle duality of light.

The statement should indicate that there is evidence supporting light behaving as a wave and light behaving as a particle.

Buy the Kit

Helpful Links

*Next Generation Science Standards® is a registered trademark of Achieve. Neither Achieve nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.