Current Electricity Part 2Current Electricity Part 2

Potential Difference and Potential Difference and Electrochemical CellsElectrochemical Cells

Electrochemical CellsElectrochemical CellsA BatteryA Battery:: is a combination of electrochemical cells is a combination of electrochemical cells

Each electrochemical cell is a package of chemicals that converts Each electrochemical cell is a package of chemicals that converts chemical energychemical energy into into electrical energyelectrical energy

An An electrolyteelectrolyte is a liquid or paste that conducts electricity is a liquid or paste that conducts electricity because it contains chemicals that form ions. An example is because it contains chemicals that form ions. An example is citric acidcitric acid. .

ElectrodesElectrodes are metal strips that react with the electrolyte. Two are metal strips that react with the electrolyte. Two different electrodes, such as zinc and copper, are used in a different electrodes, such as zinc and copper, are used in a battery.battery.

One of the electrodes collects electrons. This is the One of the electrodes collects electrons. This is the negativenegative electrode.electrode.

The other electrode loses electrons. This is the The other electrode loses electrons. This is the positive positive electrode.electrode.

1) True or false: This is an electrochemical cell.2) Identify the electrolyte3) Identify the two electrodes4) Which electrode gains electrons? What is its charge?5) Which electrode loses electrons? What is its charge?

Electrochemical CellsElectrochemical CellsEssentially all electrochemical Essentially all electrochemical cells have the same cells have the same components:components:

– ElectrolyteElectrolyte

– Positive electrodePositive electrode

– Negative electrodeNegative electrode

For this reason, you can make For this reason, you can make a battery from something as a battery from something as simple as a lemon, a nail, and a simple as a lemon, a nail, and a penny. Don’t expect it to have penny. Don’t expect it to have many volts, however.many volts, however.

Electrochemical cellsElectrochemical cellsWet cells use a liquid electrolyteWet cells use a liquid electrolyte

– Example: car batteryExample: car battery

Dry cells use a paste electrolyteDry cells use a paste electrolyte

– Example: AA batteries, watch Example: AA batteries, watch batteriesbatteries

In dry cells, the electrodes can be In dry cells, the electrodes can be called terminals. Therefore, you called terminals. Therefore, you have have one negativeone negative and and one one positivepositive terminal. terminal.

Eventually, the chemicals is a dry Eventually, the chemicals is a dry cell get used up and charges can cell get used up and charges can no longer be separated.no longer be separated.

Electrochemical cellsElectrochemical cellsAlways recycle dry cells as they contain toxic heavy metals Always recycle dry cells as they contain toxic heavy metals such as nickel, cadmium, and lead.such as nickel, cadmium, and lead.

50% of all of the toxic metals in landfills comes from dry cells 50% of all of the toxic metals in landfills comes from dry cells that were disposed!that were disposed!

Some dry cells are rechargeable. When you recharge a Some dry cells are rechargeable. When you recharge a rechargeable battery, the chemical reaction is reversed. The rechargeable battery, the chemical reaction is reversed. The reverse flow of electrons restores the reactants. This prevents reverse flow of electrons restores the reactants. This prevents you from having to dispose dry cells.you from having to dispose dry cells.

A fuel cell generates electricity from a chemical reaction with a A fuel cell generates electricity from a chemical reaction with a fuel such as hydrogen. Their technology will improve in the fuel such as hydrogen. Their technology will improve in the future. These are used in electrical vehicles.future. These are used in electrical vehicles.

Potential DifferencePotential DifferencePotential difference can be thought of as how powerful an energy Potential difference can be thought of as how powerful an energy source is.source is.

Think back to previous years Science of the topic of potential energy.

Potential energy is stored energy that can be released at any point.

An apple on a tree has potential energy. If it falls, its potential energy will be converted to motion.

Which apple has higher potential energy?

The higher apple of course. When it falls, it will fall at a greater force than the lower apple.

Potential DifferencePotential Difference

What gives electrons the force to move through a What gives electrons the force to move through a circuit?circuit?

As you know, electrons have a negative charge. As you know, electrons have a negative charge. Negative Negative chargescharges are attracted to are attracted to positive chargespositive charges. Therefore, to get . Therefore, to get electrons to move, you need positive charges.electrons to move, you need positive charges.Energy sources such as batteries have potential energy. They Energy sources such as batteries have potential energy. They create negative and positive charges. That is, they create create negative and positive charges. That is, they create potential difference.potential difference.In an In an electrochemical cellelectrochemical cell, the chemicals in the electrolyte , the chemicals in the electrolyte causes a difference in charge between the causes a difference in charge between the two terminalstwo terminals. One . One terminal is given mostly negative charges, and the other is given terminal is given mostly negative charges, and the other is given mostly positives charges. mostly positives charges. This creates potential differenceThis creates potential difference, because there is now , because there is now potential energy for the electrons to travel from the negative potential energy for the electrons to travel from the negative terminal to the positive terminal.terminal to the positive terminal.

4.5 V

Potential DifferencePotential DifferenceSo the more negative and So the more negative and positive charge is given to the positive charge is given to the terminals, the more potential terminals, the more potential difference!difference! The greater the potential The greater the potential difference, the more difference, the more powerfulpowerful the energy source!the energy source!Potential difference is measured Potential difference is measured in in volts (V).volts (V). High voltage High voltage means means high potential high potential differencedifference..Remember, high voltage is Remember, high voltage is powerful, therefore it is powerful, therefore it is dangerous!dangerous!

VoltmeterVoltmeter

You can measure voltage with You can measure voltage with voltmeter. For example, you can voltmeter. For example, you can measure the voltage of a battery. measure the voltage of a battery. Place one connecting wire to the Place one connecting wire to the negative terminal and the other negative terminal and the other connecting wire to the positive connecting wire to the positive terminal.terminal.An AA alkaline battery would An AA alkaline battery would have 1.5 V, or higher. If it’s have 1.5 V, or higher. If it’s below 1.3 V, it’s probably not below 1.3 V, it’s probably not powerful enough, and it needs to powerful enough, and it needs to be replaced.be replaced.Rechargeable batteries have Rechargeable batteries have lower voltage. However, most lower voltage. However, most devices can still accept them.devices can still accept them.

Potential DifferencePotential Difference

Review Questions Review Questions

1.1. What is a circuit?What is a circuit?2.2. Identify and describe the components of a circuit.Identify and describe the components of a circuit.3.3. What is an electrochemical cell? Name the 3 basic What is an electrochemical cell? Name the 3 basic

components of an electrochemical cell.components of an electrochemical cell.4.4. What is potential difference? How does it affect the What is potential difference? How does it affect the

flow of electrons?flow of electrons?5.5. How is potential difference measured?How is potential difference measured?6.6. What are the two types of currents?What are the two types of currents?7.7. How is current measured?How is current measured?

HomeworkHomework

Practice Questions on WorksheetPractice Questions on Worksheet

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