AP Physics 2 - Light

Electromagnetic Waves

• James Clerk Maxwell

  • Showed how the electric and magnetic fields could be viewed as a single electromagnetic field with properties

    • Time-Varying magnetic field produces a Time-Varying electric field

    • Vice versa

• An accelerating charge produces an electromagnetic wave

  • Electric and magnetic fields are perpendicular to each other and to the direction of propagation of the wave

• All EM waves are transverse

  • Electric Field and Magnetic Field are perpendicular to each other and the direction of energy flow

• Travel in straight line

Wave Types

• Largest to smallest wavelength

• Smallest to largest frequency

  • Radio

  • Micro

  • Infrared

  • Visible Spectrum

    • White Light

      • Separates into colors

      • Isaac Newton

      • ROYGBIV

  • Ultraviolet

  • X-Ray

  • Gamma

Light Detection

• The Human Eye

  • Detect changes in size, brightness, color

Sources of Light

• Luminous Bodies

  • Light emitted by the object

  • Sun, stars, sparks, fireflies

  • Rate at which light is given off is called luminous flux

    • P

    • Units: lumen (lm)

• Illuminated Bodies

  • Light reflected by the object

  • Moon, Mirror, etc

  • Illuminance is the amount of light that strikes a surface

    • E

    • Units: Lm/m², lux (lx)

Transmission of Light

• Transparent

• Translucent

• Opaque

Color

• Newton

  • White light

  • Visible spectrum

• Formation of white light

  • Additive Process

    • Primary

      • Red, Green, Blue

    • Secondary

      • Cyan, Yellow, Magenta

    • Complementary

• Pigment

  • Primary

    • Yellow, Cyan, Magenta

    • Absorb one primary and reflect two secondary of light

  • Secondary

    • Green, Red Blue

    • Absorb two primary and reflect one secondary of light

Light Behavior

• Reflection

  • Law of Reflection

    • Angle of incidence is equal to the angle of reflection

  • Incident ray, reflected ray, and normal all must be in the same plane

• Regular Reflection

  • All individual rays have same angle of reflection

• Diffuse Reflection

  • All individual rays have different angles of reflection

  • Rough surface

• Refraction of Waves

  • change in the direction of waves at the boundary between two different media

  • bending

  • Law of refraction

    • n₁sinθ₁ = n₂sinθ₂

    • n = index of refraction

      • optical density

      • n = C / V_medium