Electromagnetic Waves

Electromagnetic Wave Properties Electromagnetic waves do not need a medium to propagate. They can travel in a vacuum. The speed of all electromagnetic radiation in a vacuum is a constant. c = 3 X 108 m/s.

Electromagnetic Spectrum Draw out the spectrum noting trends in frequency, wavelength, wave speed and energy. There is a easy mnemonic to help you remember the order of EM radiation…. Red Martians Invade Venus Using X-ray Guns Radio, Microwave, Infrared, Visible, Ultraviolet, X-ray, Gamma Wavelength…Starts Long and gets shorter towards Gamma Frequency……Starts Low and gets higher towards Gamma Speed is the same for all EM waves Energy…Starts low and gets higher towards Gamma

Visible Light Colors Addition vs. Subtraction of Color The perceived color of an object is due to two processes, addition and subtraction of colors. The addition of color is the projection of various intensities of the primary colors of light to produce the desired color. The subtraction of color is the absorption of specific colors by pigments. The colors that remain produce the desired color. The reflection of white light off a colored object is an example of color subtraction.

Visible Light Primary and Secondary Colors Light-Additive Primary Colors: Red Green Blue Secondary Colors: Cyan Yellow Magenta Pigments-Subtractive Primary Colors: Cyan Yellow Magenta Secondary Colors: Red Green Blue

Visible Light Color Examples Stare blankly at a colored object for a minute.

Visible Light

Visible Light Color Examples Stare blankly at a colored object for a minute.

Visible Light

Reflection Definition of Reflection The turning back of a wave. Law of Reflection Angle of Incidence = Angle of Reflection. i = r  or ‘theta’ is a symbol used to denote a variable angle. (It is like ‘x’ in algebra.)

Refraction Definition of Refraction Definition of Index of Refraction The bending of a wave disturbance as it passes at an angle from one medium to another due to a change in speed. Definition of Index of Refraction The ratio of speed of light in a vacuum to its speed in a given transparent medium.   

Index of Refraction of Common Items Vacuum 1.00 Air 1.0002926 (we round to 1.0) Water 1.33 Common Glass 1.5 Diamond 2.42

Refraction Bending Rules The ray bends towards the normal, ni < nr. Light traveling from a less dense to more dense medium slows down. The ray bends towards the normal, ni < nr. Light traveling from a more dense to less dense medium speeds up. The ray bends away from the normal, nr < ni.   

ni sini = nr sinr Snell’s Law n = index of refraction  = angle i = incident ray r = refracted ray

Example #1 What is the index of refraction of a medium in which the speed of light is 1.85 X 108 m/s?

Example #2 A fisherman shines a flashlight at a fish swimming underwater. If the refracted ray makes an angle of 35.0 with normal, what is the angle of incidence? 

Total Internal Reflection Definition of Total Internal Reflection The complete reflection of light at the boundary of two transparent media. The effect occurs when the angle of incidence exceeds the critical angle for a light ray going from a more dense medium to a less dense medium. Definition of Critical Angle The minimum angle of incidence for which total internal reflection occurs. This occurs when the angle of refraction becomes 900.

Lenses Convex Lens Converging Lens Focal Point Focal Length Real Image Location at which rays parallel to the principal axis converge to or appear to diverge from for a convex or concave lens respectively. Focal Length Distance from the focal point to the center of the lens. Real Image An image formed when rays of light actually intersect at a single point.

Lenses Concave Lens Diverging Lens Focal Point Focal Length Location at which rays parallel to the principal axis converge to or appear to diverge from for a convex or concave lens respectively. Focal Length Distance from the focal point to the center of the lens. Virtual Image An image formed by light rays that only appear to intersect

Ray Diagram Rules for Lenses

Ray Diagram Lens Trends Case Converging or Convex Lens Diverging or Concave Lens Size Orientation Image do > 2f do = 2f 2f > do > f do = f do < f

Converging or Convex Lens Diverging of Concave Lens Ray Diagram Lens Trends Converging or Convex Lens Diverging of Concave Lens Focal Length Object Distance Image Distance Real Image Virtual Image Object Height Image Height

Lens Equation do= object distance di = image distance f = focal length

Example #4 Example #4 If an object is placed 15 cm in front of a converging lens with a focal length of 10 cm, how far from the lens should the card be placed in order to find a clear image?

Interference Interference Diffraction Polarization Doppler Effect Pattern of constructive and destructive interference. Diffraction The spreading of waves into a region behind an obstacle. Polarization The alignment of electromagnetic waves. Doppler Effect A frequency shift that is the result of relative motion between the source of sound waves and an observer.