Material Properties

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Electrical conductivity Noun

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[i-lek-tri-kuhl kon-duhk-tiv-i-tee]

Back

Electrical conductivity

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A measure of a material's ability to allow the movement of charge carriers, which forms an electric current.

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Example: This diagram shows that in a conductor, free electrons move randomly (left) until a voltage is applied, which forces them to flow in one direction (right).

Front

Charge carriers Noun

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[chahrj kar-ee-ers]

Back

Charge carriers

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Mobile particles, such as electrons or ions, whose collective movement through a material constitutes an electric current.

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Example: This diagram of a copper atom shows a single valence electron in its outer shell, which is a charge carrier because it can move freely between atoms.

Front

Valence electrons Noun

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[vey-luhns i-lek-trons]

Back

Valence electrons

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Electrons located in the outermost shell of an atom that are responsible for participating in chemical bonds.

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Example: This diagram of an oxygen atom shows electrons orbiting the nucleus in shells. The six electrons in the 'Outer shell' are its valence electrons.

Front

Insulator Noun

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[in-suh-ley-ter]

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Insulator

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A material that is a poor conductor of electricity because its valence electrons are very tightly bound.

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Example: This diagram shows a magnified electrical wire, where the outer plastic coating acts as an insulator, preventing electricity from escaping the inner copper conductor.

Front

Plasma Noun

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[plaz-muh]

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Plasma

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An ionized state of matter with high electrical conductivity due to the presence of free-moving electrons and ions.

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Example: This image shows five examples of plasma, the fourth state of matter, including natural phenomena like lightning and human-made technology like fluorescent lights.

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Ions Noun

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[ahy-ons]

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Ions

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Atoms or molecules that possess a net electrical charge from either losing or gaining one or more electrons.

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Example: This diagram shows an ionic solid (like salt) dissolving in water. The solid breaks apart into positive ions (cations) and negative ions (anions).

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Stress Noun

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[stres]

Back

Stress

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A measure of the internal forces within an object per unit of cross-sectional area, acting as a reaction to external forces.

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Example: A downward force from a weight causes a beam to bend, demonstrating how an external force creates stress within a material.

Front

Tensile stress Noun

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[ten-sahyl stres]

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Tensile stress

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The internal stress that occurs within an object when it is being pulled apart or stretched by external forces.

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Example: The diagram on the left shows tensile stress, where outward pulling forces (F) stretch a material from its original length (L₀), causing it to elongate.

Front

Compressive stress Noun

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[kuhm-pres-iv stres]

Back

Compressive stress

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The internal stress that occurs within an object when it is being pushed together or compressed by external forces.

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Example: This image shows a person applying a pushing force to an object, which causes the material of the object to be squeezed or compressed.

Front

Strain Noun

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[streyn]

Back

Strain

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A unitless measure of the fractional change in an object's size or shape that occurs in response to stress.

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Example: This diagram shows that strain is the measure of how much a material deforms. A rod with an original length (L) stretches by an amount (δ) when pulled, and strain is the ratio of this stretch to the original length.