Topic 5 - Portable Power Electrolyte: Wet or dry substance that conducts electricity because it can form ions. Eg. Salt water, battery acid An electrochemical cell or cell is a single unit that can produce an electric current. There are two parts: Electrodes:Must be made of two different metals

A chemical reaction takes place between the electrolyte and the electrodes causing the electrons to accumulate at the negative end and the protons to gather at the positive end. If hooked in a circuit, the electrons travel from the negative end to the positive end.

Wet cells use a liquid electrolyte. Dry cells –the electricity-producing cells, referred to as 'batteries', are called dry cells, because the chemicals used in them are a paste. Several cells connected in series produces a higher voltage, and is commonly referred to as a battery, which is a sealed case with only two terminals. (Page 301)

A primary cell is one in which the reactions will not continue after the reactants are used up. A secondary cell uses chemical reactions, which can be reversed. These are referred to as rechargeable batteries.

Types of ‘dry’ cells zinc-carbon Uses: Flashlights, portable stereos, CD players, walkmans Pros and Cons: Not efficient at low temperatures

alkaline Uses: Flashlights, portable stereos, CD players, walkmans Pros and Cons: Last longer than zinc carbon, but more expensive

zinc-air Uses: Calculators, hearing aids, watches Pros and Cons: Highest energy per unit mass, but discharge rapidly

Secondary Dry Cells nickel-cadmium Uses: Electric shavers, laptops, powertools, portable TV’s Pros and Cons: Rechargeable hundreds of times

nickel-metal hydride Uses: Cameras, laptops, cell phones, hand tools, toys Pros and Cons: Less toxic than NiCad – 40% more energy density than NiCad, rechargeable, no memory effect, lose charge when stored

Secondary Wet Cells lead acid Uses: Cars, motorbikes, snowmobiles, golf carts Pros and Cons: Dependable, but heavy and has a corrosive liquid