Electrical Circuits

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					Electrical Circuits
          Electric Current
• Electrons in motion.
• Current: The number of electrons that
  pass a specific point in a circuit in one
  second
• Current in an electrical circuit acts like the
  water current of a river.
• Current is measured in Amperes (A)
            Types of current
• Direct current: electrons that flow in the same
  direction in a wire. (DC)
• From batteries
• Alternating current: electrons that flow in
  different directions in a wire. (AC)
• From Generators
• Used in your home
• Transformers change AC to DC
                 Voltage
• The reason electric charge flows from
  one place to another is voltage.
  a. Voltage is the difference between two
  places where electrons are flowing.
  b. Voltage is the “push” that makes
  electrons move.
  c. Measured in volts (V).


                 HIGH
                                        LOW
                 Resistance
• Resistance: the force opposing the flow of
  electrons.
• Anything that uses electricity has resistance like
  a light bulb, heater, or oven.
• Measured in ohms
• Symbol is Greek letter omega 
• Thicker wire- less resistance
• Longer wire- more resistance
• Conductors- low resistance
• Insulators- high resistance
                    Ohm’s Law
• The relationship among current (I), voltage
  (V), and resistance (R).
• Ohm’s law states that the current in a circuit
  is equal to the voltage divided by the
  resistance
• V=IR
• R = V/I
• I=V
      R
            Do the Math
• A car has a 12 volt system. The
  headlights are on a 10 amp circuit. How
  much resistance do they have?
• Your house uses 120 volts. What amount
  of current would flow through a 20 ohm
  resistor?
              Series Circuits
• In a series circuit the
  current has only one
  path it can travel
  along.
• When any part of a
  series circuit is
  disconnected, no
  current flows through
  the circuit. This is
  called an open circuit.
             Series Circuits
• The amount of current is the same at all
  points in a series circuit.
• Old fashioned Christmas lights were in series
  so if one light went out, all the lights went
  out.
             Parallel Circuits
• Parallel circuits
  contain separate
  branches for current
  to move through.
• More current flows
  through the paths of
  lowest resistance.
• The potential
  difference is the same
  in each branch.
              Parallel Circuits
• In parallel circuits the current can take more than
  one path.
• Because there are multiple branches, the current
  is not the same at all points in a parallel circuit.
 Advantages of parallel circuits
Parallel circuits have two big advantages
 over series circuits:
 1. Each device in the circuit sees the
 full battery voltage.
 2. Each device in the circuit may be
 turned off independently without
 stopping the current flowing to other
 devices in the circuit.

				
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