14/09/09

Portable power packs.

If you are going to be absolutely correct, you should call a torch battery a dry cell. Is called dry because it has no liquid in it a battery is made up from a collection of cells joined together. A 9v. Transistor radio battery contains small calls joined in series a 12v. Car battery contains six 2v. Lead-acid cells joined in series.

There are many different cells in use today. Here six of them, with their advantages and disadvantages.

The dry cell:

Is the most commonly used cells. It is often used intorches.It is cheap, easily carried and has no liquid to spill.

The mercury cell:

Can be made into small ´´button cells´´. Even very small mercury cells can produce large currents for a short time or small currents for a long time.

The lead-acid cell:

Can produce large currents. A battery of lead-acid cells can produce the large current needed to start a car. The cell can be recharged when flat. It is heavy and contains acid which can spill.

The reserve cell:

Does not work until salt water is added. Then it can give a high current for a short time or a small current for a long time.

The lithium cell:

Is small and light. It is very reliable and long lasting. Lithium cells are expensive.

The nickel-cadmium cell:

Is the rechargeable battery sold in the shops? It is light and is completely sealed. It cannot give very large currents and is expensive.

Questions.

1 What is a battery?-Is a dry cell.

How a car battery is made up?-it´s made up from a collection of cells joined together.

2.Heaning acids only use small currents. Suggest two reasons why a mercury cell is a good cell for running a hearing acid.

Because it has a long current and a short current.

3. A) suggest reasons why the dry cell is the most commonly used cell.

-It is cheap, easily carried and has no liquid to spill

b) If you leave a torch on, the bulb gradually gets glimmer. Why?

4 .One of the six cells can be found in a life raft. Which cell is this? The reserve cell:

Does not work until salt water is added.

Why might it be used for?

It might be used in the oceans to help to active products needed.

5.try to find out: What heart Pacemakers are. Then suggest why lithium cells are used to power them.