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.
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)
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”