Electromagnetic Spectrum, Light Behavior, and Human Vision: Key Concepts and Wave Interactions

Order of electromagnetic spectrum

Radio, Microwave, Infrared, Visible, Ultraviolet, X-ray, Gamma

Visible light color with highest frequency and energy

Violet

Source of ALL electromagnetic waves

Accelerating electric charges

Speed of EM waves in a vacuum

Yes, they all travel at the speed of light

Wave behavior proving particles act like waves

Double-slit interference

Effect of light entering a denser medium

It slows down and bends toward the normal

Index of refraction

A measure of how much light slows in a material

Where light travels fastest

In a vacuum (and faster in warm air than cool air)

Total internal reflection

Full reflection within a denser medium when angle exceeds critical angle

Clear part of underwater vision when looking up

A cone of about 96 degrees

Law of reflection

Angle of incidence equals angle of reflection

Cause of dispersion of light in a prism

Different wavelengths bend differently

Why the sky is blue during the day

Blue light scatters the most in the atmosphere

Why sunsets are red

Blue light scatters out after traveling a longer path in atmosphere

Destructive interference

Wave troughs and crests cancel out to lower amplitude

Resulting amplitude of 4 m and 3 m waves in destructive interference

1 m

Polarization in light

Restricting light vibrations to one plane

Best type of polarization for driving sunglasses

Vertical polarization (blocks horizontal glare)

Thin-film interference

Wave reflections cancel or reinforce different colors due to film thickness

Blackbody radiation

Light emitted by a heated object depending on temperature

E = hf

Photon energy increases with frequency (h is Planck's constant)

Continuous spectrum

Emitted by hot dense objects (like filament bulbs)

Emission spectrum

Bright lines from excited gas

Absorption spectrum

Dark lines where gas absorbs specific wavelengths from continuous light

Fluorescence

Quick light emission after absorbing UV light

Phosphorescence

Delayed light emission (afterglow)

Most energy-efficient light source

LED

LASER

Light Amplification by Stimulated Emission of Radiation

Characteristics of laser light

Coherent, in-phase, and one color (monochromatic)

Photoelectric effect

Electrons are ejected when light above a frequency hits a material

Factors affecting number of electrons in photoelectric effect

Brightness (intensity of light)

Factors affecting speed (energy) of photoelectric electrons

Frequency of light

Alpha decay

Atom emits helium nucleus → atomic number goes down by 2, mass by 4

Beta decay

Neutron turns into proton and electron → atomic number goes up by 1

Resulting element when thorium (90) emits an alpha particle

Radium (88)

Why gamma rays don't bend in magnetic fields

They have no charge

Metastable state

A long-lived excited atomic energy level

EM wave with shortest wavelength

Gamma ray

EM wave with longest wavelength

Radio wave

Determining bending of light in materials

Index of refraction (higher means more bending)

Color of visible light with highest energy per photon

Violet

Path of light between two points according to Fermat

Path of least time

Effect of light absorption on materials

They warm up (energy converts to heat)

Waves that diffract most

Long wavelengths (like AM radio)

Part of the eye that detects color

Cones

Part of the eye that detects low light

Rods