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