Ch. 8: Ohm’s Law
Current, Voltage & Resistance
8.1 Electric Potential Energy & Voltage
• 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)
Battery
An electrochemical cell
Electrochemical cell
Converts stored chemical energy
into electrical energy
Battery Terminals
Positive or Negative End points
where a connection can be made
Battery
Terminals
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 Pile
Invented the first battery in 1799
Alessandro 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)
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)
1. The amount of Charge that has been
separated (Coulombs)
• Electrochemical cells (batteries) separate positive &
negative charges
• The greater the difference, the greater the amount of
charge (Coulombs) in this battery
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)
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 electricity
Dry cell – moist paste
Wet cell – battery solution
Producing Voltage
Electrodes
• 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