Matter & Energy


Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.

Electric Circuits

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An electric circuit is an arrangement of electric current sources and conducting paths through which a current can continuously flow. In a simple circuit consisting of a small light bulb, a battery, and two pieces of wire, the electric current flows from the negative terminal of the battery, through one piece of connecting wire, through the bulb filament (also a type of wire), through the other piece of connecting wire, and back to the positive terminal of the battery. When the electric current flows through the filament, the filament heats up and the bulb lights.

A switch can be placed in one of the connecting wires. A flashlight is an example of such a circuit. When the switch is open, the connection is broken, electric current cannot flow through the circuit, and the bulb does not light. When the switch is closed, current flows and the bulb lights.

The bulb filament may burn out if too much electric current flows through it. To prevent this from happening, a fuse (circuit breaker) may be placed in the circuit. When too much current flows through the fuse, a wire in the fuse heats up and melts, thereby breaking the circuit and stopping the flow of current. The wire in the fuse is designed to melt before the filament would melt.

The part of an electric circuit other than the source of electric current is called the load. The load includes all appliances placed in the circuit, such as lights, radios, fans, buzzers, and toasters. It also includes the connecting wires, as well as switches, fuses, and other devices. The load forms a continuous conducting path between the terminals of the current source.

There are two basic ways in which the parts of a circuit are arranged. One arrangement is called a series circuit, and the other is called a parallel circuit.

A. Series Circuits
B. Parallel Circuits
C. Series-Parallel Circuits
D. Series and Parallel Sources