Download electric circuit

Circuits
The Electric Force and the Electric Field
•
The force between charged objects is
an electric force.
• An electric field is the region around
a charged object in which an electric
force is exerted on another charged
object.
Parts of a Circuit
•
Forming a Loop An electric
circuit is a complete, closed path
through which electric charges
flow.
• All circuits need three basic
parts: an energy source, wires,
and a load.
Law of Electric Charge
Parts of a circuit
Series and Parallel Circuits
Key Question:
How do series and parallel circuits work?
Series and Parallel Circuits
 In
series circuits, current can only
take one path.
 The
amount of current is the same
at all points in a series circuit.
Adding resistances in series

Each resistance in a
series circuit adds to
the total resistance of
the circuit.
Total resistance in a series circuit

Light bulbs, resistors, motors, and heaters usually have
much greater resistance than wires and batteries.
Voltage
 Voltage
is the rate at which
energy is drawn from a source
that produces a flow of electricity
in a circuit; expressed in volts
Voltage in a series circuit
 Each
separate resistance
creates a voltage drop as
the current passes through.
 As current flows along a
series circuit, each type of
resistor transforms some of
the electrical energy into
another form of energy
Series and 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.
Series and Parallel Circuits
 When
analyzing a parallel circuit,
remember that the current always has
to go somewhere.
Voltage and current in a parallel circuit
In a parallel circuit the voltage is the
same across each branch because
each branch has a low resistance
path back to the battery.
 The amount of current in each branch
in a parallel circuit is not necessarily
the same.
 The resistance in each branch
determines the current in that branch.

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.
Short circuit

A short circuit is a parallel path in a circuit with
zero or very low resistance.

Short circuits can be made accidentally by
connecting a wire between two other wires at
different voltages.

Short circuits are dangerous because they can
draw huge amounts of current.
Resistance in parallel circuits
Adding resistance in parallel provides
another path for current, and more
current flows.
 When more current flows for the same
voltage, the total resistance of the
circuit decreases.
 This happens because every new path
in a parallel circuit allows more
current to flow for the same voltage.

Electric Power, AC, and DC
Electricity
Key Question:
How much does
electricity cost
and what do you
pay for?
Electric Power, AC, and DC
Electricity

The watt (W) is a unit of power.

Power is the rate at which energy moves
or is used.

Since energy is measured in joules,
power is measured in joules per second.

One joule per second is equal to one
watt.
Power in electric circuits
One watt is a pretty small amount of
power.
 In everyday use, larger units are more
convenient to use.
 A kilowatt (kW) is equal to 1,000 watts.

Paying for electricity

Electric companies charge for
the number of kilowatt-hours
used during a set period of time,
often a month.

One kilowatt-hour (kWh) means
that a kilowatt of power has
been used for one hour.

Since power multiplied by time
is energy, a kilowatt-hour is a
unit of energy.
Electric Current
• AC and DC There are two kinds of electric
current—direct current (DC) and alternating
current (AC).
Alternating and direct current
 DC—Direct
Current—produced
by solar cells and
chemical cells
(batteries)
 Current only flows
in one direction.
 One end of the
battery is positive
and the other end
is negative.
Alternating and direct current
 AC—Alternating
Current
 Current flows back
and forth
(alternates)
 Found in homes
 Generators
produce AC current
Application: Wiring in Homes and
Buildings
Application: Wiring in Homes and
Buildings
Toll Road—Circuit Analogy
Toll Booth Explanation
 Adding
toll booths in series
increases resistance and slows
the current flow.
 Adding toll booths in parallel
lowers resistance and
increases the current flow.
Batteries in Series & Parallel:
Charge It
What a Shock!

How Objects become charged

Friction


Contact


Two objects rubbed together
Transfer by conduct
Induction

Rearranging charges within an object without
touching it.
Static Electricity

Buildup of electric charges on an object
Static means – not moving
 Shocked lately?

Moving Charges
•
An electrical conductor is a
material in which charges can
move easily.
•
An electrical insulator is a
material in which charges
cannot move easily.
Electric changes
•
•
Static electricity is the electric
charge at rest on an object.
The loss of static electricity as
charges move off an object is called
electric discharge. One of the most
dramatic examples of electric
discharge is lightning. The next slide
shows how lightning is formed.