© Houghton Mifflin Harcourt Publishing Company Section 3 Current and Resistance Chapter 17 Current and Charge Movement Electric current is the rate at which electric charges pass through a given area.

© Houghton Mifflin Harcourt Publishing Company Click below to watch the Visual Concept. Visual Concept Chapter 17 Section 3 Current and Resistance Conventional Current

© Houghton Mifflin Harcourt Publishing Company Section 3 Current and Resistance Chapter 17 Drift Velocity Drift velocity is 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.

© Houghton Mifflin Harcourt Publishing Company Click below to watch the Visual Concept. Visual Concept Chapter 17 Section 3 Current and Resistance Drift Velocity

© Houghton Mifflin Harcourt Publishing Company Section 3 Current and Resistance Chapter 17 Resistance to Current Resistance is 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

© Houghton Mifflin Harcourt Publishing Company 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 called ohmic materials. Ohm’s low does not hold for all materials. Such materials are called non-ohmic. Resistance depends on length, cross-sectional area, temperature, and material.

© Houghton Mifflin Harcourt Publishing Company Click below to watch the Visual Concept. Visual Concept Chapter 17 Section 3 Current and Resistance Factors that Affect Resistance

© Houghton Mifflin Harcourt Publishing Company 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. Potentiometers have variable resistance.

© Houghton Mifflin Harcourt Publishing Company Section 4 Electric Power Chapter 17 Objectives Differentiate between direct current and alternating current. Relate electric power to the rate at which electrical energy is converted to other forms of energy. Calculate electric power and the cost of running electrical appliances.

© Houghton Mifflin Harcourt Publishing Company Section 4 Electric Power Chapter 17 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. –In alternating current, the direction of charge movement continually alternates.

© Houghton Mifflin Harcourt Publishing Company Section 4 Electric Power Chapter 17 Energy Transfer Electric power is the rate of conversion of electrical energy. Electric power P = I∆V Electric power = current  potential difference

© Houghton Mifflin Harcourt Publishing Company Click below to watch the Visual Concept. Visual Concept Chapter 17 Section 4 Electric Power Energy Transfer

© Houghton Mifflin Harcourt Publishing Company Section 4 Electric Power Chapter 17 Energy Transfer, continued Power dissipated by a resistor Electric companies measure energy consumed in kilowatt-hours. Electrical energy is transferred at high potential differences to minimize energy loss.

© Houghton Mifflin Harcourt Publishing Company 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.

© Houghton Mifflin Harcourt Publishing Company Click below to watch the Visual Concept. Visual Concept Chapter 18 Schematic Diagram and Common Symbols Section 1 Schematic Diagrams and Circuits

© Houghton Mifflin Harcourt Publishing Company Section 2 Resistors in Series or in Parallel Chapter 18 Resistors in Series A series circuit describes two or more components of a circuit that provide a single path for current. Resistors in series carry the same current. The equivalent resistance can be used to find the current in a circuit. The equivalent resistance in a series circuit is the sum of the circuit’s resistances. R eq = R 1 + R 2 + R 3 …

© Houghton Mifflin Harcourt Publishing Company Chapter 18 Section 2 Resistors in Series or in Parallel Resistors in Series

© Houghton Mifflin Harcourt Publishing Company 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.

© Houghton Mifflin Harcourt Publishing Company 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. Section 2 Resistors in Series or in Parallel

© Houghton Mifflin Harcourt Publishing Company Chapter 18 Sample Problem, continued Resistors in Series 1. Define Given: ∆V = 9.0 V R 1 = 2.0 Ω R 2 = 4.0 Ω R 3 = 5.0 Ω R 4 = 7.0 Ω Section 2 Resistors in Series or in Parallel Unknown: R eq = ? I = ? Diagram:

© Houghton Mifflin Harcourt Publishing Company Click below to watch the Visual Concept. Visual Concept Chapter 18 Comparing Resistors in Series and in Parallel Section 2 Resistors in Series or in Parallel

© Houghton Mifflin Harcourt Publishing Company 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

© Houghton Mifflin Harcourt Publishing Company Chapter 18 Section 2 Resistors in Series or in Parallel Resistors in Parallel

© Houghton Mifflin Harcourt Publishing Company 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. Section 2 Resistors in Series or in Parallel

© Houghton Mifflin Harcourt Publishing Company Chapter 18 Sample Problem, continued Resistors in Parallel 1. Define Given: ∆V = 9.0 V R 1 = 2.0 Ω R 2 = 4.0 Ω R 3 = 5.0 Ω R 4 = 7.0 Ω Section 2 Resistors in Series or in Parallel Unknown: R eq = ? I = ? Diagram:

© Houghton Mifflin Harcourt Publishing Company Chapter 18 Section 2 Resistors in Series or in Parallel Resistors in Series or in Parallel

© Houghton Mifflin Harcourt Publishing Company 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.

© Houghton Mifflin Harcourt Publishing Company Click below to watch the Visual Concept. Visual Concept Chapter 18 Analysis of Complex Circuits Section 3 Complex Resistor Combinations

© Houghton Mifflin Harcourt Publishing Company Section 3 Complex Resistor Combinations Chapter 18 Sample Problem Equivalent Resistance Determine the equivalent resistance of the complex circuit shown below.