chapter 8
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Chapter 8. Ohm’s law describes the relationship of current, voltage, and resistance. Terminology. Battery: is a combination of electrochemical cells connected together - PowerPoint PPT PresentationTRANSCRIPT
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.
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)
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
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
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
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