Lesson Plan

State the speed of light in a vacuum and describe how the speed of light changes in a physical medium

Describe the behavior of electromagnetic radiation — refraction at a boundary, thin-film interference, and polarization

Solve quantitative problems using c = fλ

Solve quantitative problems using illuminance = P/(4πr²) and explain the inverse-square dependence on distance

15.2

"In a vacuum, all electromagnetic radiation travels at the same incredible speed of 3.00 × 10⁸ m/s, which is equal to 671 million miles per hour. This is one of the fundamental physical constants. It is referred to as the speed of light and is given the symbol c." "When light travels through a physical medium, its speed is always less than the speed of light... When light changes speeds at a boundary between media, it also changes direction. The greater the difference in speeds, the more the path of light bends." "Because ray 2 travels a greater distance, the two rays become out of phase... This causes interference, which reinforces the intensity of the wavelengths of light that create the bands of color." "Light with an electric field that vibrates in only one direction is called polarized." "A useful equation involving c is $c = f \lambda$ where f is frequency in Hz, and $\lambda$ is wavelength in meters." "The number of lumens per square meter is called illuminance, and is given in units of lux (lx)... $\text{illuminance} = \frac{P}{4 \pi r^2}$."