CHAPTER 8: Ohm’s law describes the Relationship of

current, voltage, and resistance.

UNIT 3: Electricity

ENERGY (E) – the ability to do workENERGY (E) – the ability to do work

There are many forms of Energy

kinetic, mechanical,

chemical, solar...

RECALL:

KINETIC ENERGYKINETIC ENERGY POTENTIAL ENERGYPOTENTIAL ENERGY

Energy of motion stored Energyex: spring, elastic

band

Types of Energy

When + and – charges are pulled apart there are attractive forces wanting to put them back together, this is a form of potential energy as it has the ability to do work!

Electric Potential Energy and Voltage

Section 8.1 page 250

Stored electrical energy such as that stored in a battery

Electric Potential Energy

Electrochemical Cell (Battery)

Converts:Chemical Energy

Electrical Energy+ and – charges are

separated into terminals located at either end of the cell, when connected – charges (electrons) travel towards the + (positive) terminal as the – charges repel one another

Batteries have electric potential Energy because the stored e-’s have the ability to do work, i.e. run your CD player!

An Electrochemical Cell Requires:

different electrodes (usually metals also Carbon)

And an electrolyte (electrolytic solution)

Change in potential energy per coulomb of charge

Measured in volts (V) by a voltmeter

Electric Potential Difference (Voltage)

Analogy!

Stairs = the voltage

Backpack = amount of charge separated

More work has been done in B, therefore it has a greater Potential Energy!

Electric CircuitElectric Circuit

A complete pathway that allows electrons to flow

Transforms electrical energy into other forms of Energy

Interactive website

Section 8.2 Electric Current page 260

Electric Circuit Analogy

Parts of an Electric Circuit

Conductor – wire through which current flows

Load – converts electrical E into other forms of E

Switch – turn circuit on or off

Source – source of electrical E

Interactive Website on Switches

Circuit Diagram Symbols

Interactive Website on Circuit Diagrams

SampleCircuit Diagra

m

THE CONTINUOUS FLOW OF CHARGE (ELECTRONS) IN A

COMPLETE CIRCUIT

Current Electricity

•the amount of charge passing a given point in a conductor per second

•measured in amperes (A) by an ammeter or (mA) by a galvanometer

Electric Current

Electrical Resistance:Electrical Resistance:Slows down the

flow of electrons and transforms electrical E into other forms of E

Electrical E

Light

Heat

Sound

Motion

etc

Resistance & Ohm’s Law Section 8.3 page 270

• Measured in ohms (Ω)

•Equal to the ratio of the voltage to the current

R = V/I

RESISTANCE

Current Dependent on Potential (voltage)Current Dependent on Potential (voltage)

Current Dependent on ResistanceCurrent Dependent on Resistance

Resistance and Current Analogy:

Factors Affecting

the Amount

of Resistance

in a wire

include:

1. Length

2. Diameter (thickness)

3. Type of wire

4. Temperature

Resistance in a Light BulbLong, Thin Tungsten

wire

Short, Thick copper wire

The Mathematical Relationship comparing

voltage (V), current (I) and resistance (R)

V = IR

Interactive website Simulation

Ohm’s Law

Ohm’s Law – The VIR Tree

V

I R

Various Forms of Ohm’s Law

V=IR

I = V R

R = V I

Where:

V = voltage measured in volts (V)

I = current measured in amperes (A)

R = resistance measured in ohms (Ω)

STEP 1: Read and reread the question. Step up variables with known information.

V = ?I= 0.5AR= 2Ω

Use a question mark for the unknown value you are trying to find. Be sure to include units (V,A,Ω)

Sample Problem: What voltage is used to run a flashlight with

a 2 Ω resistor at a current of 0.5 A?

STEP 3: Convert units if necessary, measurements must be in V for voltage, A for current and Ω for

resistance. Fill in the information given in the question (including

units).

STEP 2: Determine the form of ohm’s law needed to solve for the unknown in the

question.

V = IR

V =IRV = (0.5A)(2.0Ω)

V= 1.0 V

The flashlight would require a voltage of 1.0 V.

STEP 4: Multiple or divide to calculate the unknown as per the formula chosen

in step 3.Be sure to include units in your answer,

round digits if necessary.

Used to control CURRENT or potential difference

(VOLTAGE) in a circuit

Resistor

RESISTANCE AND OHM’S LAWPAGE 278-9

Core lab Activity: