Lesson+12

Grade Level: 12

Unit: Physics

Assignment type: Lab exercises

Lesson objectives (include 2 or 3): Student will understand Student will be able to
 * How light behaves according to the wave principle.
 * How refraction of light can change the direction of a light wave and separate different wavelengths of light.
 * How reflection of light results in real and virtual images.
 * Test the principles of reflection, refraction, diffraction and interference in the laboratory.

Time required to complete this lesson: 2 to 3 lab sessions

Title of lesson: Properties of light lab

Resources/materials needed: Lamps, various mirrors (flat, concave, convex), ripple tanks, slitted barriers for the ripple tanks, prisms.

Description of lesson (if you were to describe to a parent what was happening in the classroom for this lesson, what would you say in a few paragraphs). This series of lab exercises helps the student to understand various properties of light. A couple of these principles can be demonstrated with ripple tanks filled with water. When vibrated, the water in the ripple tank forms waves that behave very similarly to light waves. When the waves encounter a slitted barrier in the ripple tank, waves concentrate as they exit the slit, resulting in more energetic waves over smaller areas beyond the slit. This phenomenon is called **diffraction**. When multiple adjacent slits are present in the barrier, the waves exiting these can sometimes cancel each other out when waves diverging from adjacent slits collide. This phenomenon is called **interference**. When encountering matter that it can penetrate, light waves bend. This phenomenon is called **refraction**. Refraction results in the formation of images of objects in which the apparent location of the image is different from the location of the actual object. The angle of refraction differs according to the wavelength of visible light, and this can be demonstrated best with a prism, which spreads the wavelengths into a visible spectrum of colored light (rainbows form by the same principle as sunlight shines through raindrops). When light cannot penetrate an object, it is **reflected** to some degree and otherwise absorbed. The colors of objects are representative of the wavelengths of light that are reflected (white objects reflect almost all light while black objects absorb almost all light). Mirrors reflect light waves in a uniform direction so they can reflect an image back to our eyes with very little distortion. Light waves that reflect from a mirror converge upon a point in space called the **focal point** where an especially sharp image is formed. An image formed at the focal point is a **real image**; an image formed at a point other than the focal point is a **virtual image**. The shape of a mirror influences the location of the focal point.

Assignment (homework or in-class: this is how the learner will practice the learning that has just occurred): Lab exercises that demonstrate the above principles.

Technology used: No technology other than the Resources/Materials listed above are required, however, videos or Power Point slides can be used to clarify the principles listed above.

The technology used in this lesson changes the teaching / learning in this way: Facilitates the description of concepts associated with the properties of light.