# 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
• 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.
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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 views: 1 posted: 8/4/2012 language: pages: 12