Big Ideas
Electricity

An electrical charge is an electrical property of matter that creates a force between objects. There are two types of charges, positive and negative. Positive charges are associated with protons and negative charges are associated with electrons. If there is an equal balance between protons and electrons (positive and negative charges) then the object will have no net charge. When an objects balance of protons and electrons is offset, the object becomes charged. The magnitude of the imbalance is directly related to the magnitude of the overall charge. If an object has more electrons than protons it will have a overall negative charge.

Opposite charges attract each other and like charges repel each other. Charged particles do this because of electrical force. Electrical force is the attraction or repulsion between two objects due to their charge. The force between two charged particles is dependent on the strength of their charges and the distance between the two charges. Its force is directly proportional to their charges and is inversely proportional to the square of the distance between the two objects.

Some materials are good conductors, that is they can transfer charges easily and some materials are good insulators, that is they do not transfer charges.

Electric potential energy is the potential energy of a charged object due to its position in an electrical field. (i.e. the closer two like charges are together the greater the electrical potential energy). The difference in electric potential energy between two positions is called a potential difference. This is measured in volts (Joule/coulomb). When charges move from a position of high electric potential energy to a position of lower electric potential energy, the rate that electric charges move through the conductor is called current. When the conductor slows down the speed of energy transfer (current), we call it a resistor. The relationship between voltage current and resistance can be expressed like this: R=V/I where R is the resistance, V is the voltage and I is the current.

Electrical circuits provide a path for movement of electrical charges between two positions of differing electric potential energy. When appliances (resistor) are placed in series in an electrical circuit, electrons have a single path to follow. Because of this, all devices (resistors) that are in the series circuit will receive the same amount of current. Devices can also be set up in parallel. In this situation, there are more than one paths for electrons two follow. Because of this, the sum of the current through all of the devices equals the total current.

 Experiences Patterns Explanations Sparks shooting off "Old Sparky" (a Van de Graaff generator)     Balloons Rubber Glass Wool       Batteries Light bulbs conducting wires Getting shocked by a door handle after walking across carpet Getting shocked by "Old Sparky"   A balloon sticks to things after you rub it with a piece of wool. Glass repels rubber     Light bulb can only light when circuits are complete Lights are brighter in series Lights are not as bright in parallel Electrons are traveling to a place of lower electrical potential energy       Opposite charges attract       Electrons need a complete path to complete a circuit. Electrons go from higher electrical potential energy to an area of lower potential energy. Series circuits give only one path for electrons to follow Parallel circuits give more than one path for electrons to follow
 Objectives Can you indicate which pairs of charges will repel and which will attract? Can you describe the relationship between resistance, current, and voltage? Can you make a circuit with resistors on parallel and in series?