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.
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)
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.