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Electric Current Electric Current • The rate at which electrical charges flow through a wire or conductor is called electric current. Electrical current = charge passing through a given area / time I = Δq/Δt SI Unit = C/s = Amperes (A) Electric Current Sample Problem The current in a light bulb is 0.835 A. How long does it take for a total charge of 1.67 C to pass a point in the wire? I = Δq/Δt Δq = 1.67 C I = 0.835 A Δt = Δq/I = 1.67 C / 0.835 A = 2.00 s Electric Current • Charges flow from high voltage to low voltage. – A voltage difference is the push that causes charges to move. – Voltage difference is measured in volts (V). – For charges to flow, the wire must always be connected in a closed path, or circuit. Electric Current Electric field travels at the speed of light, but the charges do not!!! Drift Velocity: The net velocity of a charge moving in an e- field. Types of Current • 2 Types: 1. Direct current (DC) - Electrical charges move only in one direction. - Batteries always generates a direct current (why?……fixed voltage difference). Direct Current Types of Currents (cont.) 2. Alternating current (AC) - Electrical charges are constantly changing directions. - Commonly used in homes and businesses throughout the world. Why? More efficient for long-distance electrical charge transmission. Alternating Current Sources of electrical current • A dry cell battery produces a voltage difference – zinc container – carbon suspension rod – causing current to flow between them. • Example: AA battery Dry Cell Battery Sources of electrical current (Cont.) • A wet cell battery contains two connected plates made of different metals in a conducting solution. –Example: Car battery Sources of electrical current (Cont.) Generators - Convert mechanical energy to electrical energy. - Can produce both direct and alternating current. Sources of electrical current (Cont.) • Wall sockets have a voltage difference across the two holes of an electrical outlet. – generator at a power plant provides this voltage difference.