Topic 5 :Portable Power

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Science 9 Unit D Electrical Science and
Technology

• Topic 5 Portable Power

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What is a Cells Function?

• To make a circuit work, energy must be generated
  so that electrons will flow through a resistor.
  The energy is supplied in many circuits by a
  battery or cell.
• A cell relies on chemicals to create its energy
  and is therefore called an electrochemical cell.
  The chemical reactions in the cell determine how
  much voltage can be produced. A typical alkaline
  cell can produce 1.5 V.

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Parts of an Electrochemical Cell

• Any cell contains two metal electrodes and an
  electrolyte.
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• One electrode acts as an electron donor and
  electrons leave this electrode. This electrode is
  negatively charged and is called the anode.
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• The other electrode acts as an electron acceptor
  and electrons move towards this electrode. This
  electrode is positively charged and is called the
  cathode.
• An electrolyte is a substance either a liquid or
  a paste that can conduct electricity.

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The Electrochemical Cell in Action

• As the anode donates its electrons its atoms
  become positive ions (cations) and dissolve into
  the electrolyte.
• As the electrons continue to move from anode to
  cathode the anode gradually disappears into the
  electrolyte. This is how an electrochemical cell
  eventually dies.

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How do you keep the current flowing in an EC Cell?

• If there was no electrolyte then the cell would
  work for an instant and then turn off. Why?
• Electrons move from negative to positive charges.
  However electrons moving to the cathode would
  make it negative and the current would stop. How
  do we keep the copper cathode neutral and the
  electrons moving?
• By putting the cathode in a solution of its own
  ions. The positive copper ions move to the copper
  metal as it becomes negative, keeping it neutral.
  You actually the copper strip getting bigger.
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• The ions need to be able to move back and forth
  so that the electrolytes stay neutral and the
  current keeps moving.

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Types of Batteries

• Primary batteries batteries that cannot be
  recharged. Once the reactants are used up
  (electrodes and electrolytes) the battery is
  dead.
• Secondary batteries batteries that can be
  recharged. An electric current is forced through
  the battery which reverses the chemical reaction
  and builds back up the reactants. Over time,
  however, the electrode metals dissolve completely
  into the electrolyte.
• In an automobile, while the car is moving, the
  alternator turns a generator which forces an
  electric current back into the lead acid car
  battery. This process allows a car battery for
  many years.
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• Wet cell A cell that uses a liquid (usually an
  acid) electrolyte.
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• Dry Cell A cell that uses a solid (usually a
  paste) electrolyte.
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• Voltaic Pile The first kind of battery invented
  in the 1700s by Alessandro Volta. It consists of
  alternating pieces of metal (the electrodes)
  separated by salt water.

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Animal Electricity

• Animal Electricity Luigi Galvani discovered
  that there is electricity in the tissue of
  animals. Attaching a battery/cell to the nerves
  of an animal can cause them to twitch. (This was
  the idea behind Frankenstein).

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Commonly Used Cells and Batteries