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 / Vmedium

Critical Angles

  • Going from larger n value to smaller n value

  • Is an incident angle that produces refracted angle of 90°

  • Full Internal Reflection

    • Any angle greater than critical angle

    • No refracted ray

Mirrors

  • sheet of glass with reflective material on the back

  • Types of mirrors

    • Plane (Flat)

    • Concave (bends inward)

      • Converging mirror

      • All light rays converge at small range of points in front of mirror

    • Convex (bends outward)

      • Diverging mirror

      • No light rays overlap

  • Object

    • Where the light is coming from

    • Luminous or illuminated body

    • Every point on object produces light in every direction

    • Object Distance

      • Center of object to center of mirror

    • Object Height

  • Image

    • What is perceived

    • Where actual/extended reflected rays intersect

    • Image Distance

      • Image to mirror

    • Image Height

    • Virtual

      • Rays intersecting behind the mirror

    • Real

      • Rays intersecting in front of the mirror

  • Center of Curvature

  • Focal Point

    • Focal Length

      • Distance from focal point to mirror

      • Half the radius of curvature

  • Principle Axis (Optical Axis)

    • The normal of the mirror drawn through the center of curvature and the focal point