Refraction and Rainbows

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Objective

SWBAT explain the similarities and differences between refraction, reflection and diffraction.

Big Idea

In this hands on lesson, students work to discover how rainbows are made, discover what happens to the way a pencil looks when half of it is placed in water. .

Engage

5 minutes

I begin this lesson by reviewing what electromagnetic waves are.  I tell students that a wave of light will travel in a straight line until it encounters an obstacle or is encountered by a force.  Then I show this video. 

 

Explore, Explain, and Elaborate

60 minutes

For this part of the lesson, I give students 2 glass beakers and 2 pencils, although any straight object will work. (I prefill the beakers since my classroom only has one sinc.  I fill one beaker with water, and leave the other empty.) Next, I instruct students to place the pencil into the empty beaker and observe it from the side.  I direct students to write some observational notes in their science notebooks about how the pencil looks.  Then, I direct students to put the other pencil in the water and look from the same angle. Students should be able to see a bend in the appearance of the pencil, especially if they focus at the water line.  I instruct students to write brief observational notes in their science notebooks about the pencil in the water. 

Listen in as this students tries to explain what is happening.  He notices a difference in how the pencil looks but struggles to come up with exactly what he wants to say. 

 


Next I show students the refraction handout  (Refraction handout Explanation) and lead a brief discussion about refraction.  I ask students to explain refraction in their own words by writing about what they observed in their notebooks. 

Next, I tell students that rainbows form when light is refracted off raindrops. If the sun is at the right angle, different drops will refract different colors.  Then I show this video about how rainbows are made to help clear up misunderstandings about refraction.  

insert student video of refraction definition here)

 

 

 

Evaluate

10 minutes

As students make observations during this lesson, I informally assess their knowledge of the information presented.  Since NGSS 4-PS4-2 states that students will develop a model to describe that light reflecting from objects and entering the eye allows objects to be seen, as I'm informally observing students, I focus on whether or not students understand reflection.