Diffraction Monochromatic light Polychromatic light the spreading of a wave around the edge of a barrier or through an opening Monochromatic light consists of only one color (wavelength). Polychromatic light consists of more than one color (wavelength).

“Each point on a wavefront acts as a new source of disturbance.” Huygen’s Principle is used to explain diffraction. “Each point on a wavefront acts as a new source of disturbance.”

Click here to read about Christiaan Huygens. Click here and here to view simulations of Huygen’s Principle. Huygen’s Principle can be used to explain reflection and refraction, as shown here.

x d l = L Young’s Double Slit Interference x d x L l is the wavelength of light d is the distance between slits x is the distance from the central bright band to the first order bright line L is the distance from slits to screen

Click here and here to view simulations of double slit interference. Notice changes in the interference pattern as each variable changes.

Click here, here, here, and here to view single slit interference simulations. Notice how the pattern changes as each variable is manipulated.

Single Slit Interference Characteristics central bright band pattern spreads out as wavelength increases pattern spreads out as distance to screen increases pattern spreads out as distance between slits decreases Similar results occur with a narrow single slit. Single Slit Interference Characteristics central bright band narrower slit produces wider central band larger wavelength gives wider pattern

Diffraction Gratings series of many slits etched on film Diffraction gratings (or replica gratings) will separate light into its component colors through diffraction and interference. They are often used to identify the component colors of polychromatic light.

Click here to view a simulation of a diffraction grating. Notice the changes in the diffraction pattern as the variables are manipulated.

Thin Film Interference The color spectrum seen in a soap bubble, or any thin film, results from the interference of the reflections of light from the front and back surfaces of the film. The colors seen depend on the thickness of the film. The light most strongly reflected has a wavelength such that the film thickness is an odd multiple of l/4. Other wavelengths will suffer partial or total destructive interference.