PhysicsPhysicsElectric CircuitsElectric Circuits

– V = I x RV = I x R– Power (Watts) = IPower (Watts) = I22 x R = I x V x R = I x V– Series and parallel circuitsSeries and parallel circuits

Today’s AgendaToday’s Agenda

• Unit OverviewUnit Overview

• Begin Static ElectricityBegin Static Electricity– Electric chargesElectric charges– Electric forcesElectric forces– FieldsFields

PhysicsPhysicsElectric and Magnetic Electric and Magnetic

PhenomenaPhenomena

California State California State StandardsStandardsPhysics: Electric and Magnetic PhenomenaPhysics: Electric and Magnetic Phenomena

5. Electric and magnetic phenomena are 5. Electric and magnetic phenomena are related and have many practical related and have many practical applications. As a basis for applications. As a basis for understanding this concept:understanding this concept:a. a. Students know Students know how to predict the voltage or how to predict the voltage or

current in simple direct current (DC) electric current in simple direct current (DC) electric circuits constructed from batteries, wires, circuits constructed from batteries, wires, resistors, and capacitors.resistors, and capacitors.

b. b. Students know Students know how to solve problems how to solve problems involving Ohm’s law.involving Ohm’s law.

California State California State StandardsStandardsc. c. Students know Students know any resistive element in a DC any resistive element in a DC

circuit dissipates energy, which heats the circuit dissipates energy, which heats the resistor. Students can calculate the power (rate resistor. Students can calculate the power (rate of energy dissipation) in any resistive circuit of energy dissipation) in any resistive circuit element by using the formula element by using the formula Power = Power = IR IR (potential difference) ×(potential difference) ×I I (current) = (current) = II22RR..

d. d. Students know Students know the properties of transistors and the properties of transistors and the role of transistors in electric circuits.the role of transistors in electric circuits.

e. e. Students know Students know charged particles are sources of charged particles are sources of electric fields and are subject to the forces of the electric fields and are subject to the forces of the electric fields from other chargeselectric fields from other charges..

California State California State StandardsStandards

f. f. Students know Students know magnetic materials and electric magnetic materials and electric currents (moving electric charges) are sources currents (moving electric charges) are sources of magnetic fields and are subject to forces of magnetic fields and are subject to forces arising from the magnetic fields of other arising from the magnetic fields of other sourcessources..

g. g. Students know Students know how to determine the direction how to determine the direction of a magnetic field produced by a current of a magnetic field produced by a current flowing in a straight wire or in a coilflowing in a straight wire or in a coil..

h. h. Students know Students know changing magnetic fields changing magnetic fields produce electric fields, thereby inducing produce electric fields, thereby inducing currents in nearby conductors.currents in nearby conductors.

i. i. Students know Students know plasmas, the fourth state of plasmas, the fourth state of matter, contain ions or free electrons or both matter, contain ions or free electrons or both and conduct electricity.and conduct electricity.

California State California State StandardsStandards

j.* j.* Students know Students know electric and magnetic fields electric and magnetic fields contain energy and act as vector force fields.contain energy and act as vector force fields.

k.* k.* Students know Students know the force on a charged the force on a charged particle in an electric field is particle in an electric field is qE, qE, where where E E is the is the electric field at the position of the particle and electric field at the position of the particle and q q is the charge of the particle.is the charge of the particle.

l.* l.* Students know Students know how to calculate the electric how to calculate the electric field resulting from a point charge.field resulting from a point charge.

m.* m.* Students know Students know static electric fields have as static electric fields have as their source some arrangement of electric their source some arrangement of electric charges.charges.

California State California State StandardsStandards

n.* n.* Students know Students know the magnitude of the force on the magnitude of the force on a moving particle (with charge a moving particle (with charge qq) in a magnetic ) in a magnetic field is field is qvB qvB sin(sin(aa), where ), where a a is the angle is the angle between between v v and and B B ((v v and and B B are the magnitudes are the magnitudes of vectors of vectors v v and and B, B, respectively), and students respectively), and students use the right-hand rule to find the direction of use the right-hand rule to find the direction of this force.this force.

o.* o.* Students know Students know how to apply the concepts of how to apply the concepts of electrical and gravitational potential energy to electrical and gravitational potential energy to solve problems involving conservation of solve problems involving conservation of energy.energy.

Electric CircuitsElectric Circuits

LightLightBulbBulb

Some Electrical SymbolsSome Electrical Symbols

BatteryBattery

LampLamp

SwitchSwitch(open)(open)

WireWire

++ CapacitoCapacitorroror

ResistorResistor

DiodeDiode

+

SchematicsSchematics

Switches Break The Switches Break The CircuitCircuit

Series CircuitSeries Circuit

Parallel CircuitParallel Circuit

Amps Kill!Amps Kill!Current Current ininamperesamperes

EffectEffect

0.0010.001

0.0050.005

0.0100.010

0.0150.015

0.0700.070

Can be feltCan be felt

PainfulPainful

Involuntary muscle Involuntary muscle contractions (spasms)contractions (spasms)

Loss of muscle controlLoss of muscle control

If through the heart, serious If through the heart, serious disruption; probably fatal if disruption; probably fatal if current lasts for more than one current lasts for more than one secondsecondSource: Conceptual Physics, page 537

Ohm’s LawOhm’s Law

• V = IRV = IR I = V/RI = V/R R = V/IR = V/I

• Voltage = Current x ResistanceVoltage = Current x Resistance

• Current = Voltage/ResistanceCurrent = Voltage/Resistance

• Resistance = Voltage/CurrentResistance = Voltage/Current

• V = Voltage (Volts) VV = Voltage (Volts) V

• I = Current (Amperes, amps) AI = Current (Amperes, amps) A

• R = Resistance (Ohms) R = Resistance (Ohms) ΩΩ

Resistance in a Series Resistance in a Series CircuitCircuit

• R R (total)(total) = R = R11 + R + R22 + R + R33 + … + …

++

R1

R2R3

Resistance in a Parallel Circuit Resistance in a Parallel Circuit (1)(1)

• R R (total)(total) = (R = (R11 x R x R22) / (R) / (R11 + R + R22))

• 1/R 1/R (total)(total) = 1/R = 1/R11 + 1/R + 1/R22

++

R1R2

Resistance in a Parallel Circuit Resistance in a Parallel Circuit (2)(2)

• 1/R 1/R (total)(total) = 1/R = 1/R11 + 1/R + 1/R22

• R R (total)(total) = (R = (R11 x R x R22) / (R) / (R11 + R + R22))++

R1

R2

PowerPower

•Power (Watts) = IPower (Watts) = I22 x R = I x V x R = I x V

•Power = Current x VoltagePower = Current x Voltage

AC-to-DC Converter AC-to-DC Converter (Rectifier)(Rectifier)

AC-to-DC Converter AC-to-DC Converter (Rectifier)(Rectifier)

AC-to-DC Converter AC-to-DC Converter (Rectifier)(Rectifier)