Current and Charge Movement

1. Section 3 Current and Resistance Chapter 17 Current and Charge Movement • Electric currentis the rate at which electric charges pass through a given area.

2. Section 3 Current and Resistance Chapter 17 Conventional Current Click below to watch the Visual Concept. Visual Concept

3. Section 3 Current and Resistance Chapter 17 Drift Velocity • Drift velocityis the the net velocity of a charge carrier moving in an electric field. • Drift speeds are relatively small because of the many collisions that occur when an electron moves through a conductor.

4. Section 3 Current and Resistance Chapter 17 Drift Velocity Click below to watch the Visual Concept. Visual Concept

5. Section 3 Current and Resistance Chapter 17 Resistance to Current • Resistanceis the opposition presented to electric current by a material or device. • The SI units for resistance is the ohm (Ω) and is equal to one volt per ampere. • Resistance

6. Section 3 Current and Resistance Chapter 17 Resistance to Current, continued • For many materials resistance is constant over a range of potential differences. These materials obey Ohm’s Law and are calledohmic materials. • Ohm’s low does not hold for all materials. Such materials are callednon-ohmic. • Resistance depends on length, cross-sectional area, temperature, and material.

7. Section 3 Current and Resistance Chapter 17 Factors that Affect Resistance Click below to watch the Visual Concept. Visual Concept

8. Section 3 Current and Resistance Chapter 17 Resistance to Current, continued • Resistors can be used to control the amount of current in a conductor. • Salt water and perspiration lower the body's resistance. • Potentiometershave variable resistance.

9. Chapter 17 Section 4 Electric Power Objectives • Differentiatebetween direct current and alternating current. • Relateelectric power to the rate at which electrical energy is converted to other forms of energy. • Calculateelectric power and the cost of running electrical appliances.

10. Chapter 17 Section 4 Electric Power Sources and Types of Current • Batteries and generators supply energy to charge carriers. • Current can be direct or alternating. • In direct current, charges move in a single direction. • Inalternating current, the direction of charge movement continually alternates.

11. Chapter 17 Section 4 Electric Power Energy Transfer • Electric power is the rate of conversion of electrical energy. • Electric power P = I∆V Electric power = current  potential difference

12. Chapter 17 Section 4 Electric Power Energy Transfer Click below to watch the Visual Concept. Visual Concept

13. Chapter 17 Section 4 Electric Power Energy Transfer, continued • Power dissipated by a resistor • Electric companies measure energy consumed inkilowatt-hours. • Electrical energy is transferred at high potential differences to minimize energy loss.

14. Section 1 Schematic Diagrams and Circuits Chapter 18 Schematic Diagrams • A schematic diagram is a representation of a circuit that uses lines to represent wires and different symbols to represent components. • Some symbols used in schematic diagrams are shown at right.

15. Section 1 Schematic Diagrams and Circuits Chapter 18 Schematic Diagram and Common Symbols Click below to watch the Visual Concept. Visual Concept

16. Section 2 Resistors in Series or in Parallel Chapter 18 Resistors in Series • Aseriescircuit describes two or more components of a circuit that provide a single path for current. • Resistors in series carry the same current. • Theequivalent resistancecan be used to find the current in a circuit. • The equivalent resistance in a series circuit is thesum of the circuit’s resistances. Req = R1 + R2 + R3…

17. Section 2 Resistors in Series or in Parallel Chapter 18 Resistors in Series

18. Section 2 Resistors in Series or in Parallel Chapter 18 Resistors in Series, continued • Two or more resistors in the actual circuit have the same effect on the current as one equivalent resistor. • The total current in a series circuit equals the potential difference divided by the equivalent resistance.

19. Section 2 Resistors in Series or in Parallel Chapter 18 Sample Problem Resistors in Series A 9.0 V battery is connected to four light bulbs, as shown at right. Find the equivalent resistance for the circuit and the current in the circuit.

20. Resistors in Series 1. Define Given: ∆V = 9.0 V R1 = 2.0 Ω R2 = 4.0 Ω R3 = 5.0 Ω R4 = 7.0 Ω Unknown: Req = ? I = ? Diagram: Section 2 Resistors in Series or in Parallel Chapter 18 Sample Problem, continued

21. Section 2 Resistors in Series or in Parallel Chapter 18 Comparing Resistors in Series and in Parallel Click below to watch the Visual Concept. Visual Concept

22. Section 2 Resistors in Series or in Parallel Chapter 18 Resistors in Parallel, continued • Resistors in parallel have the same potential differences across them. • The sum of currents in parallel resistors equals the total current. • The equivalent resistance of resistors in parallel can be calculated using a reciprocal relationship

23. Section 2 Resistors in Series or in Parallel Chapter 18 Resistors in Parallel

24. Section 2 Resistors in Series or in Parallel Chapter 18 Sample Problem Resistors in Parallel A 9.0 V battery is connected to four resistors, as shown at right. Find the equivalent resistance for the circuit and the total current in the circuit.

25. Resistors in Parallel 1. Define Given: ∆V = 9.0 V R1 = 2.0 Ω R2 = 4.0 Ω R3 = 5.0 Ω R4 = 7.0 Ω Unknown: Req = ? I = ? Diagram: Section 2 Resistors in Series or in Parallel Chapter 18 Sample Problem, continued

26. Section 2 Resistors in Series or in Parallel Chapter 18 Resistors in Series or in Parallel

27. Section 3 Complex Resistor Combinations Chapter 18 Resistors Combined Both in Parallel and in Series • Many complex circuits can be understood by isolating segments that are in series or in parallel and simplifying them to their equivalent resistances. • Work backward to find the current in and potential difference across a part of a circuit.

28. Section 3 Complex Resistor Combinations Chapter 18 Analysis of Complex Circuits Click below to watch the Visual Concept. Visual Concept

29. Section 3 Complex Resistor Combinations Chapter 18 Sample Problem Equivalent Resistance Determine the equivalent resistance of the complex circuit shown below.