1. Electrochemical Cells
Ms. Petrauskas

2. Voltaic cells
Chemical reactions use up some of the materials in the cell as electrons flow from it
A battery is a connection of 1 or more cells
Primary wet (voltaic)
Primary dry

3. Volta’s Voltaic Cell Developed 1800, by Alessandro Volta.
Wet, because made from two pieces of metal in a liquid
Metal terminals are usually zinc and copper; called electrodes
Liquid is an electrolyte, a fluid that conducts electricity

4. The Reaction
Takes place on the surface of the electrodes that is in contact with the electrolyte
Depends on the movement of electrons and ions

5. Dangers…. Spilling the corrosive electrolyte
Continuous need to replace the zinc and copper

6. Wet cells Liquid electrolyte
Mostly sulphuric acid (strong and inexpensive)
Volta cell is a wet cell

7. Primary dry cell Work much the same as wet cells
Moist paste instead of liquid electrolyte
When most of the negative electrode has been used up, electrons stop flowing, the battery is dead

8. Types Zinc (-ve)- carbon(+ve) (cheap, not very long lasting)
Alkaline (expensive, long lasting)
+ve manganese dioxide
-ve powdered zinc
Has a brass current collector
Button
Silver oxide or zinc air

9. Dangers…
Do not recharge disposable dry cell batteries, because it will cause them to heat up and the cell casing will break open or explode.
Overtime even an unused dry cell will gradually discharge. They can become dead without use
Disposal bad for the environment

10. Secondary cells Can be discharged and then recharged
Secondary because two chemical processes involved
Discharge
Recharge
The recharge is a result of an electric current being passed in the opposite direction
Lead acid car battery is a secondary wet cell

11. Solar cells Converts solar energy to electrical energy
Strikes semi-conductor, e- are knocked loose from atoms
E- move to create electricity

12. Why do batteries die?
Batteries die when the reactants get used up like when the zinc or sulfuric acid can no longer react.
Reactive forms change after reacting and are not easily reversed

13. Direct Current
Electrons move in one direction only!- From negative to positive
Was used to supply homes with electricity.
Still the type of electricity seen with batteries
Was found that a large amount of energy was lost this way.

14. Alternating Current
Alternating current is the flow of electrons that alternates direction in an electrical circuit
This is the type of electricity that NOW powers your home.

15. AC-how it works…
The polarity of the voltage across the wire coils reverses as the opposite poles of the rotating magnet pass by. Connected to a load, this reversing voltage polarity will create a reversing current direction in the circuit.

16. AC- Why is it better Less electricity lost over distance
Simpler generator design
Range of current possible when transformers distribute.

17. What battery properties are best?
Golf cart
Flashlight
Portable drill
Key chain light
Pacemaker
Hearing aid
Computer