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Ohm’s law describes the relationship of current,
voltage, and resistance
Terminology
 Battery: is a combination of electrochemical cells
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connected together
Electrochemical cells (or just cells): converts chemical
energy into electrical energy stored in charges. There is a
separation of charges.
Energy: the ability to do work
Kinetic Energy: energy that a moving object has because
of its motion
Potential energy: the energy stored in an object
Electric 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 charge
 The 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 Difference
 When you climb a set of stairs your body has done
work. The work done is called potential energy
 The 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 difference
 Activity 8-1B , page 255
Electric Circuit
 Electric 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 circuit
 Electrical load: any device that changes electrical
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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 energy
Conductor: 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. Current
 Analogy: 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 Electricity
 Cannot 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 diagrams
 Website: www.andythelwell.com/blobz/guide.html
 Activity 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 light
 Electrical 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
Task
 Activity 8-3A page 271 (factors affecting resistance)
Factors affecting Resistance in a
wire
 Factors that affect Resistance
 1. Type of Wire- Copper offers less resistance than
nichrome
 2. Thickness of the Wire- The thinner the wire, the
greater the resistance
 3. 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 resistance
 Ohm’s Law: I = V
R
 V = 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 calculations
 Page 273, practice problems. Use the triangle method.
V
I
R
Potential difference and Current
 Interactive websites to demonstrate how one affects
the other
 www.article19.com/shockwave/oz.htm
 Phet.colorado.edu/simulations/sims.php?sim=Circuit_C
onstruction_Kit_DC_Only
Core Lab
 Resistors and Ohm’s Law