Characteristics of Light Chapter 14 Section 1

Light Most people think of light as only being admitted from a light bulb or the sun in the form of white light. White light is the combination of multiple colors of light combined into one.

Visible Light Spectrum Red Orange Yellow Green Blue Indigo Violet

Prism A Prism can be used to separate white light into the colors of the visible light spectrum.

Particle or wave? Light can be described as a particle, as a wave, and even as a combination of the two. Wave model is best suited for introductory discussion of light.

Light Spectrum The spectrum of light is not confined to just visible light. There are many variations of light: Radio waves Microwaves Infrared (IR) Waves Visible Light Ultraviolet (UV) Light X Rays Gamma Rays

Electromagnetic Spectrum All of the different kinds of light are examples of electromagnetic waves. Electromagnetic Waves – A transverse wave consisting of oscillating electric and magnetic fields at right angles to each other.

Transverse Waves vs. Longitudinal Waves Transverse waves oscillate perpendicular to the direction of the wave propagation. Light Waves Longitudinal waves oscillate parallel to the direction of the wave propagation. Sound Waves Link: Transverse and Longitudinal Wave Animation

Electromagnetic Waves Light is composed of electric and magnetic waves. They are perpendicular to the direction they move. They are transverse waves. The electric and magnetic fields are at right angles to each other

Wave Differences Electromagnetic waves are distinguished by their difference in frequencies and wavelengths. They account for the color changes in visible light and distinguishes visible light from invisible electromagnetic radiation, such as X Rays.

Metric Prefixes

Speed of Light All forms of electromagnetic radiation travel at a single high speed in a vacuum. The speed of light in a vacuum was found to be 2.99792458x108 m/s c = 3.00x108 m/s (speed of light)

Speed of Light = frequency x wavelength Wave Speed Equation c = fλ Speed of Light = frequency x wavelength Speed of Light (c) – Units are in (m/s) Frequency (f) – Units are in (Hz) Wavelength (λ) – Units are in (m)

Example Problem What is the wavelength of infrared light with a frequency of 3.0x1012 Hz?

Example Problem Answer λ = 1.0x10-4 m

Huygens' Principle The wave nature of light can be treated as a ray. Treating the propagating wave of light as a straight line perpendicular to the wave front.

Brightness of Light The brightness of light depends on: How much light is being emitted from the source. Distance away from the source.

Brightness and Distance Apparent brightness is proportional to the actual brightness of the source divided by the square of the distance between source and observer. Lv = L/d2 Apparent Brightness = Actual Brightness ÷ distance2 Brightness – Units (cd) “candela”