Chapter 10 Current Electricity

10.1 Electricity and Electric

Current

• Electric current refers to electric

charge flowing in a circuit in a

controlled way.

• The current flows from an energy

source to a device that used

energy.

• A joule (J) is a unit for measuring

energy

• A standard light bulb uses 4000J

each minute.

• It takes 300kJ of energy to heat 1 L

of water from room temperature to

boiling

• A battery is a source of energy. It

contains two or more electric cells.

• A load is a device that converts

electrical energy to another form of

energy.

– A light bulb converts electric energy to

light and heat energy

• The pathway in a circuit is made of

metals, usually copper

Circuit Diagram Symbols

Assignment

• P. 305 #1, 2, 4-8, 10

10.2 Electric Current

• Electrons are moving in a circuit.

The current is measured in

amperes (A).

• It is measured with an ammeter.

• Ammeters are placed in series with

the lights

• Conventional current flows from the

positive terminal to the negative

terminal

• The electrons flow in the opposite

direction

• Direct current circuits have

electrons flowing in only one

direction

• Alternating current circuits have

electrons reversing direction (60 Hz

in North America)

Series Circuits

• A series circuit has current going

through the device in sequence

Parallel Circuits

• A parallel circuit splits up the

current

Assignment

• P. 309 #5, 6, 8-10

10.3 Electrical Potential

Difference

Voltage

• Energy is carried by electrons. The

type of energy is electrical potential

energy. We can only measure the

change in electrical potential energy

per coulomb. It is measured in

volts (V)

– A flashlight (2 cells) produces 3.0 volts

– Household outlets produce 120V

• A voltmeter is a device that

measures electrical potential. It can

be connected to a power source or

load. It is connected in parallel.

• Cells in parallel do not produce

more voltage, they do provide

greater charge

Cells in Series

• Total voltage equals sum of

individual cells

Cells in Combination

Assignment

• P. 314 #3-12

10.4 Resistors and Ohm’s

Law

• A resistor is a component of an

electrical circuit that resists, or

opposes, the flow of electric current

• Resistance is measured in Ohms

(Ω)

• The amount is determined by the

type of material

Ohm’s Law

• R=V/I

• I=V/R

• V=IR

• R= resistance(Ω)

• V=Voltage (V)

• I= Current (A)

Example 1

• The starter of a car is 12V. If the

motor has 75A of current, what is

the resistance?

Example 2

• A 92Ω resistor has 78mA of current,

what is the voltage?

Example 3

• A flashlight has a resistance of 10.7

Ω . The batteries provide 2.8V.

What is the current?

Assignment

• Resistors and Ohms Law

Worksheet

10.5 Resistors in Parallel and

Series Circuits

Series Circuits

• In a series circuit. Current must pass through each resistor.

• The total resistance is the sum of all the resistors

• The total voltage is the sum for each resistor’s voltage

• Current is the same for each resistor

Parallel Circuit • In a parallel circuit, some current goes down

each branch

• Adding resistors in parallel decreases total resistance

• For identical resistors, total resistance equals individual resistance divided by number of resistors

• Total voltage is equal to individual voltage for each path

• Total current equals sum of individual currents

Assignment

• P. 325 #1-2, 6-7

10.5 Resistors in Series and

Parallel

Calculations

Example 1

• Three resistors are connected in

series. The resistors measure 22

Ω, 68 Ω and 100 Ω. What is the

total resistance?

Example 2

• Three identical resistors are connected to a 120V power source

• A) What is the voltage of each resistor?

• B) An ammeter measures the current leaving the power source as 0.06A, what is the current going through the middle resistor?

• C) What is the resistance of each resistor?

Example 3

• Three identical resistors are connected in parallel to an electric cell. In the third resistor, the resistance is 63 Ω and the current is 23mA

• A) What is the voltage of the cell?

• B) What is the total resistance of the parallel group of resistors?

Assignment

• P. 322, p. 323, p. 324 Practice

Problems

• P. 325 #3-5

Review Assignment

• P. 332 #1-18