Chapter 8Ohm’s law describes the relationship of

current, voltage, and resistance

TerminologyBattery: is a combination of electrochemical cells

connected togetherElectrochemical cells (or just cells): converts

chemical energy into electrical energy stored in charges. There is a separation of charges.

Energy: the ability to do workKinetic Energy: energy that a moving object has

because of its motionPotential energy: the energy stored in an objectElectric potential energy: the electrical energy stored

in a battery is called this because the electrons have stored energy and the ability to do work after they leave the battery

Electric Potential Difference (Voltage): The amount of electric potential energy per one coulomb of chargeThe unit for measuring potential difference is

the volt(V)

Voltmeter: is a device that measures the amount of potential difference (voltage) between two locations of charge separation.

Comparing Potential Energy and Potential DifferenceWhen you climb a set of stairs your body has

done work. The work done is called potential energyThe more mass moved up the stairs the more

potential energy.

Think of potential difference in a battery as being like the height of the stairs. The amount of charge separated in a battery is like the mass moved up the stairs.

Measuring potential differenceActivity 8-1B , page 255

Electric CircuitElectric Circuit: a complete pathway that

allows electrons to flow.Electrical Charge: described as building up

at the negative terminal of the cell/battery which then flows from this terminal as negative charges repel one another.

Battery has two terminals (ends) called electrodes. Usually two different metals

Electrolyte: the electrodes are placed in this which can conduct electricity.

A reaction occurs between the electrodes and the electrolytes, leaving electrons on one electrode and taking electrons from another.

One electrode is negative and the other is left positive.

The opposite charge on each electrode means that there is a potential difference (voltage) between the two electrodes.

Parts of an electric circuitElectrical load: any device that changes

electrical energy into other forms of energy. Ex: light bulb

Control/Switch: a device that can turn the circuit on or off by closing or opening the circuit

Source: the source of electrical energyConductor: the wire through which electric

current flows.The energy is provided at the source and

then “used” by the different parts of the circuit (a potential or voltage drop occurs)

Energy around a circuit

Current Electricity: the continuous flow of charge in a complete circuit.Electrons are pushed or repelled from the

negative end of the battery along a circuit and end up on the positive terminal of the battery

Electric Current: the amount of charge passing a point in a conductor every second

Ampere (A): the SI unit used to measure current. The rate of flow of electric charge.

Ammeter: device used to measure current

Voltage vs. CurrentAnalogy: Two identical busses, identical

routes leave a school (the battery). One has more students than the other. The speed of the busses can be the same (current) but when they reach the park the bus with more students will have more energy (voltage)

Static vs. Current ElectricityCannot use static electricity to run an

electrical device

Static electricity is a charge that remains stationary

Current electricity is the continuous flow of charge

Circuit Symbols

ammeter resistor

Create circuit diagramsWebsite:

www.andythelwell.com/blobz/guide.htmlActivity 8-3C: Circuit Diagrams with

Resistors

Resistance: the property of any material that slows down the flow of electrons and converts electrical energy into other forms of energy.Ex: In high resistance wire in light bulbs, the energy

is converted to heat and lightElectrical Resistance: the ratio of the voltage to

the current.Ohm(Ω): the SI unit for electrical resistance

Analogy: running on a sandy beach versus running in knee high water. Easier to run on beach just as it is easier for electricity to flow through some materials than others

TaskActivity 8-3A page 271 (factors affecting

resistance)

Factors affecting Resistance in a wireFactors that affect Resistance1. Type of Wire‑ Copper offers less resistance

than nichrome2. Thickness of the Wire‑ The thinner the

wire, the greater the resistance3. Length of the Wire‑ The longer the wire,

the greater the resistance (coiled tungsten wire)

4. Temperature‑ The greater the temperature, the greater the resistance

Relationship between voltage, current and resistanceOhm’s Law: I = V

RV = voltage, I = current, R = resistance

The more resistance in a circuit the less current flowing

The more voltage in a circuit, the more current For example: more batteries or volts the greater

the current

Ohm’s Law calculationsPage 273, practice problems. Use the

triangle method.

V

I R

Potential difference and CurrentInteractive websites to demonstrate how one

affects the otherwww.article19.com/shockwave/oz.htmPhet.colorado.edu/simulations/sims.php?

sim=Circuit_Construction_Kit_DC_Only

Core LabResistors and Ohm’s Law