Section 2: Electric Current This section discusses electrical pressure Charges flow from high voltage areas to low voltage areas Voltage—like an electrical pressure that pushes charge

(Section 2 cont’d) Just as water or air must have a pressure difference to flow, voltage difference must be present for electric charges to flow Voltage difference—the push that causes charges to move and is measured in volts (V) (fig. 11 pg. 202)

Closed Circuits The flow of charges through a wire or any conductor is called electric current The electric current in a circuit is measured in amperes (A) Circuit—a closed, conducting path for the flow of electrons

(Section 2 cont’d.) Current is almost always the flow of electrons In order to keep current moving continuously through a circuit a power source (voltage source) is needed One common source--battery

Dry-Cell Batteries Individual batteries used in flashlights, etc.—dry cell batteries Made of a zinc container that surrounds a moist chemical paste w/a solid carbon rod suspended in the middle Provides a voltage difference between +/- terminals

(Dry-cell batteries cont’d) When the two terminals of a dry cell battery are connected in a circuit, a reaction occurs. The voltage difference between these 2 terminals causes current to flow through a closed circuit

Wet-cell batteries Wet-cell battery—contains two connected plates made of different metals or metallic compounds in a conducting solution Ex: car batteries (lead plates in sulfuric acid) The chemical reaction in ea/cell provides a voltage difference

More on Batteries In addition to batteries a voltage difference is provided at electrical outlets Household devices are designed for 120 V (standard) Some wall sockets supply 240 V Ex: electric ranges, clothes dryers, etc.

Resistance Resistance—the tendency for a material to oppose the flow of electrons, changing electrical energy into thermal energy and light All materials have some resistance Resistance is measured in ohms *type of material & wire size effect resistance

Controlling the flow of electricity So far: Voltage difference causes charges to flow An electrical resistance restricts the movement of charges ex: water flowing in a pipe

Ohm’s Law: Current = Voltage difference / resistance OR I(A) = V (V) / R (ohms) V = I R Ohm’s Law Diagram—pg. 207