Science 9: Unit D – Topic 1 Notes Electric Charges and Electrostatics

Charged Matter All substances in the universe contain atoms which contain protons (positively charged particles) and electrons (negatively charged particles). Most substances/objects contain an equal number of positive and negative charges and therefore have no net charge (they are neutral).

Positive and Negative Charges Objects become charged only if they gain or lose electrons, usually through contact with a charged object or free electrons. If a substance, through contact, or induction loses electrons it will become positively charged. If it gains electrons, it will become negatively charged. Note that only electrons move, not protons.

Laws of Charges Created by Benjamin Franklin. Describes how charged objects behave together: I. Unlike charges attract. II. Like charges repel. III. Charged objects attract neutral objects.

Conductors, Insulators, and Semiconductors Insulators are materials that do not allow the free movement of electrons. Examples include cotton, glass, and plastic. Conductors are materials, usually metals, that hold their electrons loosely and therefore can become charged easily. Semiconductors are materials that fall somewhere between conductors and insulators. Metalloids usually form semiconductors. Semiconductors are used in computer chips.

Superconductors Offer no resistance to the movement of electrons. You can run a charge through a superconductor forever without adding in any energy. Usually made from an alloy (mixture) of metals and ceramics. To work, superconductors must be operated at extremely cold temperatures (1K-100 K)

Neutralizing Unbalanced Charges Any charged object will try to become neutral by discharging the extra electrons. When you experience a shock you are experiencing an electric discharge. Grounding – Discharging an object by connecting it to the ground which can provide or absorb any extra electrons. Electric surges can be especially dangerous for electronic equipment (eg. computers).

A car grounded with a Ground Strap