Electric Circuits

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Electric Circuits

• A circuit always begins and ends in the same
  place, forming a loop

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Parts of a Circuit

• Consist of
• 1. Energy Source
• Battery, photocell, thermocouple, electric
  generator
• 2. Load - a device that uses electrical energy
  to do work
• Light bulbs, appliances, televisions, motors
• 3. Wires to connect the other parts

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Opening and Closing a Circuit

• A circuit can also contain a switch which is used
  to open and close a circuit.
• Made of 2 pieces of conducting material
• If a switch is closed, it is turned on
• If a switch is open, it is turned off
• The loop of the circuit is broken and no charges
  can flow through the circuit

4
Types of Circuits

• Most circuits contain more than one load.
• The loads in a circuit can be connected in 2
  different ways
• Series
• Parallel

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Series Circuits

• A circuit in which all parts are connected in a
  single loop
• Charges traveling through a series circuit must
  flow through each part and can only follow one
  path

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Uses for Series Circuits

• Some series circuits use a load as a switch
• The automatic door at the grocery store is
  operated by a series circuit with a motor that
  opens the door and a photoelectric device (an
  electric eye) that acts as an on/off switch
• When no light hits the device, charges flow to
  the motor and the door opens.

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• For charges to flow in a series circuit, all the
  loads must be turned on and working.
• Charges pass through one load after another, in
  order, around the circuit
• If one load is broken or missing, the other loads
  will not work.
• If your lamp and TV were connected in a series
  and the lamp broke, your TV would go off

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Parallel Circuits

• What would happen if all the lights in your home
  were connected in series.
• If you needed a light on in your room, all the
  other lights in the house would have to be turned
  on too!
• Circuits in buildings are wired in parallel,
  rather than series

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• Parallel circuit - circuit in which different
  loads are located on separate branches.
• Because there are separate branches, the charges
  travel through more than one path.

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• Unlike a series circuit, the loads in a parallel
  circuit do not have the same current in them.
• Each load in a parallel circuit uses the same
  voltage.
• Each load will use its full amount of energy.
• Each branch of the circuit can function by
  itself.
• If one load is broken or missing, charges will
  still run through the other branches and will
  continue to work.

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• It would be inconvenient if each time a light
  bulb went out, your TV or stereo stopped working.
• With parallel circuits, you can use one light or
  appliance at a time, even if another branch
  fails.

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Household Circuits

• You have many circuits in your home.
• Each circuit branches out from a breaker box or a
  fuse box that acts as the electrical
  headquarters for the building.
• Each branch receives a standard voltage, which is
  120 Volts in the US.

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AAAHHHHH

• Broken wires or water can cause a short circuit
• This occurs when charges bypass the loads in the
  circuit.
• When the loads are bypassed, the resistance of
  the circuit drops, and the current in the circuit
  increases.
• If it increases too much, it can produce enough
  thermal energy to start a fire.

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AAAAHHHHH Contd

• Circuits may also fail if they are overloaded.
• A circuit is overloaded when too many loads, or
  electrical devices are attached to it.
• If too many loads are connected to one circuit,
  the current increases to an unsafe level and can
  cause the temperature of the wires to increase
  and cause a fire.

15
Circuit Safety!

• Fuses - contain a thin strip of metal through
  which the charges for a circuit flow.
• If the current in the circuit is too high, the
  metal in the fuse warms up and melts.
• A break or a gap in the circuit is produced, and
  the charges stop flowing
• This is referred to as blowing a fuse
• The fuse must then be replaced.

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More Safety!

• Circuit breakers are switches that automatically
  open if the current in the circuit is too high.
• When this happens, a strip of metal in the
  circuit breaker warms up and bends away from the
  wires in the circuit.
• A break in the circuit results
• To fix a breaker, all you do is flip a switch
  inside the breaker box

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