ELECTRICITY AND MAGNETISM

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ELECTRICITY AND MAGNETISM
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CIRCUIT AND COMPONENTS

• BY Tanisha Alexander
• 5A

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CIRCUIT DIAGRAMS

• Cell supplies d.c. Dry cells may be rechargeable
  or non-rechargeable. Wet cells are rechargeable.
• D.c supply
• a.c supply

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CIRCUIT DIAGRAMS

• Switch- opens and closes electric and electronic
  circuits.
• Fixed resistor- resistors control current flow in
  electric circuits

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CIRCUIT DIAGRAMS

• Variable Resistor- also called a rheostat and is
  used to maintain a steady value of current.
• Filament lamp- sometimes used as a current
  detector. Consists of an evacuated glass envelope
  and a thin filament.

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CIRCUIT DIAGRAMS

• Ammeter- a current measuring device placed in
  series with the component.
• Voltmeter- a device for measuring potential
  difference and is placed in parallel with the
  component.

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CIRCUIT DIAGRAMS

• Fuse- protects wires, parts of circuits or whole
  circuits from damage by excessive currents. Fuses
  are placed in the live wire of a.c. circuits.
• Earth- this connection protects users of
  electrical equipment from electrical shocks
  caused by stray currents.

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CIRCUIT DIAGRAMS

• Junction- wires are actually connected
• Conductors crossing- wires cross but do not touch

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CIRCUIT DIAGRAMS

• Semiconductor diode- allows electron flow in one
  direction only. Used to change a.c to d.c i.e. in
  rectification.
• Battery of cells- a series combination of
  identical cells

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CELLS

• THE DRY CELL
• The common dry cell has a zinc outer case which
  serves as the negative terminal. A central carbon
  rod is the positive terminal. Ammonium Chloride
  in the form of jelly is the electrolyte. The dry
  cell also contains a mixture of powdered carbon
  and manganese dioxide. The carbon improves
  conduction, the manganese dioxide reduces
  polarization. Polarization is the process by
  which hydrogen atoms build up around the positive
  terminal of the cell or battery. Polarization
  reduces both the potential difference and the
  current that the cell can provide.

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THE PRIMARY CELL

• In a primary cell, the reactions cannot be
  reversed.
• Primary cells cannot be recharged.
• Example A Dry Cell

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THE SECONDARY CELL

• In secondary cells, the reactions can be
  reversed, therefore they can be recharged again
  and again.
• Example The Lead-acid Battery
• THE LEAD- ACID BATTERY
• The lead-acid battery has a negative plate
  made of soft lead. It normally looks grey. The
  positive plat is made of lead dioxide which is
  red and the electrolyte is sulphuric acid. When a
  battery is in use or being discharged, both the
  negative and positive plates are converted to
  lead sulphate.

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DIFFERENCE BETWEEN A PRIMARY CELL AND A SECONDARY
CELL

• PRIMARY CELL
• Primary cells are cheaper to produce
• Primary cells are easier to install
• Primary cells have higher internal resistance,
  thus they cannot supply large currents without
  being damaged

• SECONDARY CELL
• Secondary cells are more expensive to produce
• Secondary cells are harder to install
• Secondary cells have lower internal resistance,
  thus they can supply large currents without
  getting damaged.

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RECHARGING A LEAD-AID BATTERY

• The following points should be noted carefully
• The positive end of the d.c. supply is joined to
  the positive end of the battery.
• Low charging currents should be used
• he variable resistor is used to control the
  current.

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CIRCUIT DIAGRAM TO SHOW HOW THE LEAD-ACID BATTERY
CAN BE RECHARGED

• Circuit diagram

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QUIZ

• 1) Draw the symbols for a fixed resistor, a
  battery, a voltmeter and a fuse.
• 2) List and the describe the components of a zinc
  carbon dry cell
• 3) Distinguish between a primary cell and a
  secondary cell and give an example of each.
• 4)Give three points that should be noted when
  recharging a lead-acid battery.
• 5)Draw a circuit diagram to show how a lead-acid
  battery can be recharged.

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THANK YOU FOR VIEWING.Drawings were made by
Tanisha Alexander and not by a website.