Characteristics of Light: Light travels in a straight line

Susanne Lee, Lakeview School, Cottonwood, Minnesota
Based on an original activity from Carson Dellosa, Fundamentals of Light, p.7
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In this lab experience, the students will be asked questions about characteristics of light and sound and whether these energy sources travel in straight lines. The teacher briefly demonstrates light and sound travel. Students will discover that light travels in a straight line. Within small groups, students explore how to prove that light travels in a straight line using 3 cards, with a hole punched in each one, and a flashlight.

Learning Goals

Learning Goals:
1. Students will use prior knowledge.
2. Students will use critical thinking.
3. Students will investigate, test, observe, and draw conclusions.

Key Concept:
Students will investigate and discover that light travels in a straight line and cannot bend around an object.

Vocabulary Words:
1. Shadow
2. Straight
3. Characteristic
4. Demonstrate

Context for Use

Grade Level: 3-6
Class size: 20-25
Institution: General Elementary Classroom
Type of Lesson: Lab and demonstration
Time: 45 minutes
Equipment: 3 cards and a flashlight per group
It would be beneficial for students to have completed a sound unit prior to this lesson. Students will then be able to compare and contrast light and sound characteristics.
Adaptations: Must use a room that can be darkened.

Description and Teaching Materials

Materials: a flashlight, three cards with a hole punched in each one, clay or tacky, and a straw (optional-see Teaching Notes) per small group
Anticipatory Set: Students will be introduced to the lesson by the teacher asking questions about light and sound.
Questions: Does light travel in a straight line? Can light bend around an object? Can sound bend around an object?

Instruction and Modeling: Teacher demonstrates sound movement by holding a hand out in front of his/her mouth and speaking to the class. Ask: Does the hand stop the sound from traveling to you? How does the sound reach your ears?
Next, the teacher demonstrates the light movement by holding a hand in front of a flashlight beam. Ask: Did my hand stop the light? Can the light bend around my hand and shine onto the wall? Do you think that light travels in a straight line? When the class has concluded that light travels in a straight line move onto the lab portion of the lesson.

Students are then divided into small groups and are asked to investigate a way to prove that light travels in a straight line using three note cards and a flashlight.
After students find a way to prove that light travels in a straight line the students are all brought together as a large group. Each group will demonstrate for the class what they have discovered.

Conclusion: When the three holes on the cards are lined up the light travels through the holes. If the middle card is moved to one side so that the holes are not lined up the light cannot "bend" around the middle card.

Teaching Notes and Tips

Teaching Notes:
Prepare the cards ahead of time.
Students may need to use a straw to line up the three holes on the cards.
Clay or tacky work to hold the cards upright.
Light travels straight until it passes through a different material such as glass and water.
This activity is more inquiry based than how I typically use it. I have used it mostly as a demonstration in the past.


As each group shares at the conclusion of the lesson, the teacher will assess if the students are achieving the learning goals (Can the student demonstrate that light travels straight?).


3.II.C.2-Characteristics of Light

References and Resources