“BENDING” LIGHT

PRESENTATION OUTLINE Demo: Pencil Bends in Water, straw bends in water Demo: Straw Disappears in Oil, beaker disappears in oil Review: Speed of a wave depends only on medium (examples) Marching Students Example Five students come in at an angle, their direction as a whole changes Five students come in at a perpendicular angle, their direction does not change Explanation: Waves bends due to speed changes in materials and entrance angle Whiteboard predictions: beam of light and prism Practice Julius Sumner Miller Tomorrow: Seismic Waves Videos: Speed of sound video

THE BENDING OF LIGHT Observe what happens to how you “see” the object in water—which depends on the light that reaches your eyes.

THE SPEED OF A WAVE DEPENDS ON… The speed of a wave depends only on the medium through which the wave moves. Our discussion of the way waves bend and move through materials will focus on light waves. In a medium such as a vacuum or air, light waves typically move faster. In a medium such as water, glass, or other solid materials, light moves slower.

BENDING ANALOGY: MARCHING STUDENTS

REFRACTION CAUSED BY A CHANGE IN SPEED Refraction is the bending of the path of a wave as it passes from one medium (or material) into another medium. Refraction is caused by a change in the speed of the wave upon crossing the boundary between the two materials.

WHITEBOARD PRACTICE

Glass Air Illustrate the direction the light ray will be refracted. Remember, a light ray is a wave!

Glass Air

Glass Air “Normal” to the Boundary (Perpendicular)

Glass Air What if we tried the reverse? Now the light wave is going from glass to air… What happens?

Glass Air What if we tried the reverse? Now the light wave is going from glass to air… What happens? “Normal” to the Boundary (Perpendicular)

THE DIRECTION OF BENDING The direction of a light ray as it approaches the boundary is called the incident ray. The direction of a light ray after it crosses the boundary is called the refracted ray. A perpendicular line is drawn to the boundary at the point where the incident ray strikes the boundary— this is called the “normal” line, meaning “perpendicular” line. If a light ray goes from a faster medium to a slower medium, it will bend towards the normal. If a light ray goes from a slower medium to a faster medium, it will bend away from the normal. Physics Classroom: Refraction and Reflection om.com/Physics- Interactives/Refraction- and-Lenses/Refraction om.com/Physics- Interactives/Refraction- and-Lenses/Refraction

WHITEBOARD PREDICTIONS DRAW THE SITUATION AND PREDICT WHAT WILL HAPPEN TO THE LIGHT RAY.

PRACTICE The purpose of the practice is to apply the rules and natural principles discussed in class.

JULIUS SUMNER MILLER