1. 19-1: Electric Current Objectives: Describe the basic properties of electric current. Solve problems relating current, charge, and time. Differentiate between direct current and alternating current.

2. Electric Current, Resistance, and Semiconductors All electric circuits have one thing in common—they depend on the flow of electric charge. When electric charge flows from one place to another, we say it forms an electric current. The more charge that flows, and the faster it flows, the greater the electric current. In general, electric charge is carried through a circuit by electrons.

3. Electric Current, Resistance, and Semiconductors Suppose an amount of charge ΔQ flows past a given point in a wire in the time Δt. The electric current, I, in the wire is simply defined as the amount of charge divided by the amount of time. The following equation is used to determine the current flowing in a wire.

4. Electric Current, Resistance, and Semiconductors The unit of current is the ampere (A), or amp for short. It is named for the French physicist André-Marie Ampère (1775–1836). A current of 1 amp is defined as the flow of 1 coulomb of charge in 1 second: 1 A = 1 C/s A 1-amp current is fairly strong. Many electronic devices, like cell phones and digital music players, operate on currents that are a fraction of an amp.

5. 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? Given: ∆Q = 1.67 C, I = 0.835 A Unknown: ∆t = ?

6. Sources and Types of Current When you drop a ball, it falls to the ground, moving from a place of higher gravitational potential energy to one of lower gravitational potential energy. Charges have similar behavior. For example, free electrons in a conductor move randomly when all points in the conductor are at the same potential. – When a potential difference is applied across the conductor, they will move slowly from a higher electric potential to a lower electric potential. – Thus, a difference in potential maintains current in a circuit.

7. Electric Current, Resistance, and Semiconductors When charge flows through a closed path and returns to its starting point, we say that the closed path is an electric circuit. Both batteries and generators maintain a potential difference across their terminals by converting other forms of energy into electrical energy. – Batteries convert chemical energy to electrical energy – Generators convert mechanical energy to electrical energy As charge carriers collide with the atoms of a device, such as a light bulb or a heater, their electrical energy is converted into kinetic energy.

8. Types of Current In a type of circuit known as a direct-current circuit, or DC circuit, the current always flows in the same direction. Circuits that run on batteries are typically DC circuits. Circuits with currents that periodically reverse their direction are referred to as alternating- current circuits, or AC circuits. The electricity provided by a wall plug in your house is AC.

9. Direct Current (DC) Consider a light bulb connected to a battery. Because the positive terminal of the battery has a higher electric potential than the negative terminal has, charge carriers always move in one direction. Because the potential difference between the terminals of a battery is fixed, batteries always generate a direct current.

10. Alternating Current (AC) In alternating current, the terminals of the source of potential difference are constantly changing sign. Hence, there is no net motion of the charge carriers in alternating current; they simply vibrate back and forth. Alternating current is made to change direction rapidly. In the United States, alternating current oscillates 60 times every second. Thus, its frequency is 60 Hz.

12. AC vs. DC Unlike batteries, generators can produce either direct or alternating current, depending on their design. Alternating current has advantages that make it more practical for use in transferring electrical energy (Resistance). For this reason, the current supplied to your home by power companies is alternating current rather than direct current.

13. Assignment 19-1 Worksheet