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A disturbance that transfers energy from place to place.


The ability to do work or cause change.


The material through which a wave travels.


A repeated back-and-forth or up-and-down motion.


The highest point of a wave.


The lowest point of a wave.


The maximum distance the particles of a medium move away from their rest positions as a wave passes through the medium.


The distance between two corresponding parts of a wave.


The number of complete waves that pass a given point in a certain amount of time.


The unit measurement for frequency.

Electromagnetic waves

Waves that transfer electrical and magnetic energy.

Electromagnetic radiation

The energy transferred through space by electromagnetic waves.

Electromagnetic spectrum

The complete range of electromagnetic waves placed in order of increasing frequency.

Visible light

Electromagnetic waves that are visible to the human eye.


That which transmits most light without scattering it.


That which scatters light as it passes through.


Reflecting or absorbing all of the light that it strikes.

Primary colors

Three colors that can be used to make any other color.

Secondary colors

Any color produced by combining equal amounts of any two primary colors.

Complementary colors

Any two colors that combine to form white light or black pigment.


A colored chemical compound that absorbs light and can be used to color other materials.


The bouncing back of an object or wave when it hits a surface through which it cannot pass.

Law of Reflection

The rule that an angle of reflection equals the angle of incidence.

Plane mirror

A flat mirror that produces an upright, virtual image the same size as an object.


A copy of an object formed by reflected or refracted rays of light.

Virtual image

An upright image formed where rays of light appear to meet or come from.

Concave mirror

A mirror with a surface that is curved inward, like the inside of a spoon.

Optical axis

An imaginary line that divides a mirror in half.

Focal point

The point at which light rays parallel to the optical axis meet, or appear to meet, after being reflected (or refracted) by a mirror (or a lens).

Real image

An upside-down image formed where rays of light actually meet.

Convex mirror

A mirror with a surface that is curves outward.


The bending of waves as they enter a new medium at an angle.


A curved piece of glass or other transparent material that is used to refract light; the flexible structure that focuses light that has entered the eye.

Convex lens

A lens that is thicker in the middle than at the edges.

Concave lens

A lens that is thinner in the middle than at the edges.


The clear tissue that covers the front of the eye.


An opening in the center of the eye through which light enters.


The circular structure the surrounds the pupil, a ring of muscle tissue, that expands and contracts to change the size of the pupil opening


The layer of light sensitive sensory cells at the back of the eye on which an image is focused.


Receptor cells in the eye that work best in dim light and enable you to see black, white, and gray.


Receptor cells in the eye that work best in the bright light and enable you to see color.


A type of vision that sees nearby things clearly, but objects at a distance are blurred.


Able to see distant objects better than objects at close range.


An optical instrument that uses lenses to focus light, and film (or light sensitive optics) to record an image of an object


An optical instrument forms enlarged images of distance objects.

Refracting Telescope

A telescope that uses two convex lenses to form images


A lens that gathers light from an object and forms a real image.


A lens that magnifies the image formed bu the objective.

Reflecting telescope

A telescope that uses a concave mirror to gather light from distant objects.


An instrument that makes small objects look larger.

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