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

© Houghton Mifflin Harcourt Publishing Company

Section 3 Current and ResistanceChapter 17

Current and Charge Movement

• Electric current is the rate at which electric charges pass through a given area.

charge passing through a given area

electric current = time interval

QI

t


Click below to watch the Visual Concept.

Visual Concept

Chapter 17Section 3 Current and Resistance

Conventional Current



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.



Visual Concept


Drift Velocity



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

potential difference

resistancecurrent

VR

I



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.



Visual Concept


Factors that Affect Resistance



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.


Section 4 Electric PowerChapter 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.



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.



Energy Transfer

• Electric power is the rate of conversion of electrical energy.

• Electric power

P = I∆V

Electric power = current potential difference



Visual Concept

Chapter 17 Section 4 Electric Power

Energy Transfer



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.

22 ( )V

P I V I RR


Section 1 Schematic Diagrams and CircuitsChapter 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.



Visual Concept

Chapter 18

Schematic Diagram and Common Symbols

Section 1 Schematic Diagrams and Circuits


Section 2 Resistors in Series or in ParallelChapter 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.

Req = R1 + R2 + R3…


Chapter 18Section 2 Resistors in Series or in Parallel

Resistors in Series



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.

eq

VI

R


Chapter 18

Sample Problem

Resistors in SeriesA 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


Chapter 18

Sample Problem, continued

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:



Visual Concept

Chapter 18

Comparing Resistors in Series and in Parallel




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

1

Req

1

R1

1

R2

1

R3

...



Resistors in Parallel


Chapter 18

Sample Problem

Resistors in ParallelA 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.



Chapter 18

Sample Problem, continued

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:



Resistors in Series or in Parallel


Section 3 Complex Resistor CombinationsChapter 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.



Visual Concept

Chapter 18

Analysis of Complex Circuits

Section 3 Complex Resistor Combinations


Section 3 Complex Resistor CombinationsChapter 18

Sample Problem

Equivalent ResistanceDetermine the equivalent resistance of the complex circuit shown below.

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

Documents

Transcript of © Houghton Mifflin Harcourt Publishing Company Section 3 Current and Resistance Chapter 17 Current...