Electromagnetic Waves and Geometrical Optics

Vocabulary practice covering electromagnetic wave properties, the EM spectrum (including uses and dangers), the speed of light, and the basics of light reflection and ray diagrams.

Optics

The study of how light interacts with materials.

Geometrical Optics

A branch of optics that uses light rays to model mirrors, lenses, telescopes, microscopes, and prisms, focusing on the shapes of materials and the angles at which light rays hit them.

Electromagnetic (EM) Wave

A wave consisting of oscillating electric and magnetic fields that radiate outward from a source at the speed of light and can travel through empty space.

Wave

A phenomenon that transfers energy from one place to another without transferring matter.

Mechanical Waves

Types of waves that use matter to transfer energy and cannot travel in the almost empty space between the Earth and the Sun.

Transverse Wave

A wave where the direction of oscillation is perpendicular to the direction of propagation.

Longitudinal Wave

A wave where the direction of oscillation is parallel to the direction of propagation.

Frequency (EM wave)

The number of times the electric and magnetic parts of the wave vibrate each second.

Wavelength (EM wave)

The distance between the crests or troughs of the vibrating electric or magnetic parts.

Radiant Energy

The energy carried by electromagnetic waves, specifically those reaching Earth from the Sun.

EM Spectrum

The complete range of electromagnetic wave frequencies and wavelengths, ranging from radio waves to gamma rays.

Radio Waves

Electromagnetic waves with the lowest frequencies ($500\,\text{kHz}$ to about $1000\,\text{MHz}$) and wavelengths from around $1\,m$ to thousands of meters; used mainly for communications.

Microwaves

Extremely high frequency radio waves that cause water and fat molecules to vibrate; used for cooking, mobile phones, traffic speed cameras, and radar.

Cataracts

A clouding of the cornea in the eyes that can be caused by prolonged exposure to microwaves.

Infrared Waves

Waves just below visible red light in the EM spectrum, given off by hot objects and felt as warmth on the skin.

Visible Light

The tiny part of the electromagnetic spectrum that human eyes can detect, ranging from about $4 \times 10^{14}\,\text{Hz}$ to $7 \times 10^{14}\,\text{Hz}$ ($700\,\text{nm}$ to $400\,\text{nm}$).

Ultraviolet (UV) Rays

Waves with wavelengths ranging from about $4 \times 10^{-7}\,m$ ($400\,\text{nm}$) to $6 \times 10^{-10}\,m$ ($0.6\,\text{nm}$); they can cause sunburn, skin cancer, and damage to the retina.

X-rays

Very high frequency waves carrying significant energy, used in medicine and industry to see inside objects; they are produced by firing a beam of electrons at a target.

Gamma Rays

Extremely high frequency waves with a large amount of energy given off by stars and radioactive substances; they are used in radiotherapy to kill cancer cells.

Speed of Light ($c$)

The constant velocity at which all EM waves move in a vacuum, approximately $3.00 \times 10^8\,m/s$.

Ray

An arrow-headed straight line that represents the direction of propagation of light.

Beam

A collection of light rays.

Ray Diagram

A drawing that shows the path of light rays to indicate the direction the light travels.

Incident Ray

The incoming light ray that strikes a surface.

Reflected Ray

The light ray that moves away from a surface after striking it.

Normal

An imaginary line perpendicular to the surface at the point where a light ray strikes.

Angle of Incidence ($\theta_i$)

The angle measured between the incident ray and the surface normal.

Angle of Reflection ($\theta_r$)

The angle measured between the reflected ray and the surface normal.

Law of Reflection

A law stating that the angle of incidence equals the angle of reflection ($\theta_i = \theta_r$) and that the incident ray, reflected ray, and normal all lie in the same plane.

Specular Reflection

Reflection of light from a smooth shiny surface where all reflected light moves in the same direction.

Diffuse Reflection

Reflection that occurs when a surface is rough, causing reflected light to be sent out in a variety of directions.