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Ch. 8: Ohm’s Law Current, Voltage & Resistance
• Electric potential Energy increases when unlike charges move further apart• Electric potential difference (voltage) is the change
in electric potential energy per coulomb of charge• Voltage is measured in volts (V)• Electrical energy depends on the amount of charge
and voltage• Electrochemical cells (batteries) are a common
source of voltage• Voltmeters measure potential difference (voltage)
8.1 Electric Potential Energy & Voltage
BatteryAn electrochemical cell
Electrochemical cellConverts stored chemical energy into electrical energy
BatteryTerminals
Battery Terminals Positive or Negative End points where a connection can be made
Electrochemical cells/Batteries• have separate positive and negative charges• the negative terminal has excess electrons• the positive terminal has less electrons
Typical household battery (C, D, AA & AAA)• potential difference of 1.5 Volts (V)
Wall sockets• potential difference of
120 to 230 Volts (V)
Voltaic PileInvented the first battery in 1799Alessandro Volta
The Volt (V) was named in his honour
Kinetic & Potential Energy Energy• The ability to do work
Kinetic Energy• Energy a moving object
has because of its motion
Potential Energy• energy stored in an object
Electric Potential Energy
• Potential Energy: energy stored in an object
• Electric Potential Energy: Electrical energy stored in a battery
Potential Energy & Potential Difference
The potential energy in a battery is due to …
1. The amount of charge that has been separated (coulombs)
2. The potential difference/voltage (volts)
• Electrochemical cells (batteries) separate positive & negative charges
• The greater the difference, the greater the amount of charge (Coulombs) in this battery
1. The amount of Charge that has been separated (Coulombs)
The potential energy in a battery is due to …1. The amount of charge that has been separated (coulombs)2. The potential difference/voltage (volts)
2. Potential Difference(Voltage)
The pushing force of water (electricity) is due to the …height difference (potential difference/Voltage)
Voltage - like a “pushing force” of electricity - measured in volts (V)
The potential energy in a battery is due to …1. The amount of charge that has been separated (coulombs)2. The potential difference/voltage (volts)
Which has greater potential difference (voltage)?
Electric Potential Energy & Electric Potential Difference
The potential difference (voltage) in a battery is like…the height of the stairs
The amount of potential energy (charge/Coulombs) separated in a battery is like…the mass moved up the stairs
If this person were to fall from top of the stairs, in A or B, the potential difference (height) is the same
However, there’s more potential energy in B than in A because more mass (charge/Coulombs) have been separated
A
B
The Voltmeter Measures Electric Potential Difference
Voltmeters are a device that measures the amount of potential difference between 2 locations of charge separation
In this image,The battery’s voltage is measured
Volt (V) is the unit for measuring voltage
Batteries: Wet Cells or Dry Cells
Electrolyte: Substance that conducts electricityDry cell – moist pasteWet cell – battery solution
Producing VoltageElectrodes • the 2 terminals of a battery• 2 different metals (usually)
Electrolyte• Substance that conducts electricity• Acid, base or salt
In Figure 8.6 the acidic electrolyte…• pulls atoms off the Zinc and leaves
electrons on electrode• pulls electrons off the Copper electrode
Sources of Electrical Energy
1. Friction
2. Piezoelectric Crystals
3. Photo-electrochemical cells
4. Thermocouples
5. Generators