Download Electricity and Magnetism Circuits Electromahnets

Electricity and
Magnetism
Circuits
Electromagnets
Chapter 17 and 18
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The Law of
Electric Charge
 Like
charges repel
– push away
 Opposites
attract
Electric Field
A
region around a charged object in
which an electric force is exerted on
another charged object.
 How
do we create charge?
Friction
 electrons
another
are “wiped” from one object to
Conduction
 Conduction
– electrons move through
direct contact (a shock!)
Induction
• when charges are rearranged without
direct contact
What Is Static Electricity?
A stationary electrical
charge that is built up on
the surface of a material
Static Discharge
Human body can not feel less
than 2,000 volts of static
discharge
Static charge built up by
scuffing shoes on a carpet can
exceed 20,000 volts.
What is an electric circuit?
A
complete loop
(begins and ends
at the same place)
through which
electric charges
flow.
Voltage
 The
unit of measure for potential difference is the
Volt (V)
Think 9 volt battery
 The device that provides the potential difference is
considered the voltage source;
Current
 The
current is the rate at which a charge
passes a given point
 The unit for current is the ampere or Amp
(symbol - A)
 An amp is the amount of current that
flows past a point in one second
How does the flow begin?
 Electrons
in a circuit have potential
energy
 The potential energy of each charge is
called electrical potential
 In a battery, the electrical potential of
one terminal is higher than the other
terminal
 The difference in this potential energy
is called potential difference
 This potential difference causes the
loose electrons to be pulled away
from their atoms and flow through the
material
The Essential Parts of a Circuit
1.
2.
3.
An energy source – battery etc.
Wires – to carry the electric charge
Load – light bulb, radio etc.
Types of Circuits
The
parts of a circuit can
be connected in different
ways. The two main types
are:
1. Series
2. Parallel
Series Circuits
 All
 All
parts are connected in a single loop
loads in a series circuit share the same
current
Parallel Circuit
A
circuit in which loads are connected
side by side
 Current in a parallel circuit has more than
one path
 Each load receives the full amount of
energy the energy source can provide
(voltage) and they will use as much
current as they need

Ex. 45 vs. 60 Watt light bulb
Questions to Consider:

Which circuit would be more useful in lighting
a home or building?


Which circuit is used in Christmas tree lights?


It depends, they used to be made in series, if
one burned out all went out. Nowadays many
are made in parallel so the remaining bulbs will
continue to burn.
Why are series circuits useful?


Parallel, you want to be able to have the lights
on in one room and off in another.
Burglar alarms
What drawbacks are there in using parallel
circuits?
Switches
 Some
circuits in include a switch to open
and close the circuit (turn it on and off)


Open – off (the loop is broken)
Closed – on (the loop is closed or
complete)
Series Circuit
 Will
all bulbs burn with
the same brightness?

Yes, all receiving the
same electric current.
 What
will happen if I
add a bulb?

They will all dim b/c
they will receive less
electric current.
 What
happens if one
bulb burns out?

They will all go out, the
loop is no longer
complete.
Parallel Circuits
 Will
all bulbs burn with
the same brightness?

No, it depends on their
wattage.
 What
will happen if I
add a bulb?

They will continue to
burn with the same
brightness.
 What
happens if one
bulb burns out?

The remaining bulbs will
stay lit.
EXPLORING MAGNETISM
What Do Magnets Do?
Attract or repel other magnets (exert a
force)
Attract other magnetic metals
Have at least 2 distinct ends (poles) each
Magnetic Field
This is the area in which a
magnetic force can be
exerted.
Magnetic force is stronger
the closer you are to the
magnet.
Magnetic Force
Like poles repel, opposite poles
attract
Magnetic Materials
 What makes some things

magnetic, while other things
can’t be magnetized?
 Spinning electrons cause small
magnetic fields around each
atom.
 Magnetic materials have atoms
whose magnetic fields can be 
lined up in the same direction.
 Areas where atoms’ magnetic
fields line up are called
magnetic domains.
magnetic domain
Randomly arranged domains =
No magnet!
Magnetic domains lined up =
Magnet!
Permanent Magnets
 A permanent magnet is a material that
keeps its magnetic properties even
when it is NOT close to other magnets.
Electricity to Magnetism
 In 1820, H.C. Oersted
discovered that an electric
current flowing through a wire
had a magnetic field around it.
 Electricity can cause
magnetism!
 Electromagnets are powerful
magnets that can be turned on
and off.
 You can make an
electromagnet stronger by (1)
putting more turns of wire in
the coil or (2) making a larger
soft iron core, or (3)
increasing the current through
the wire.
What is a solenoid?
Electricity and magnetism are closely related.
This was first seen when a solenoid was
developed.
A solenoid is simply a coil of wire that when
current is flowing through it will generate a
magnetic field.
Electromagnet:
A stronger version of the solenoid!
It creates a temporary magnet when a currentcarrying wire coil surrounds a magnetic metal core.
Useful because they can be turned off
Adding and removing coils can increase or decrease
strength
Uses for electromagnets
 A simple DC electric motor
contains a permanent magnet, an
electromagnet, and a commutator.
When current flows through the
electromagnet, it turns within the
magnetic field of the permanent
magnet, changing electricity to
mechanical energy.
 Current meters also use permanent
magnets and electromagnets.
When current flows through a wire,
it makes an electromagnet. The
force between the electromagnet
and the permanent magnet makes
a needle move on the meter.
Magnetism to Electricity
 Joseph Henry and Michael
Faraday discovered that
magnetism could also produce
electric current. This is called
 If a magnet is moved back and
forth through a coil of wire,
current can be made to flow
through the wire. This is the
idea behind electric generators
and transformers.
Current moves left in wire.
Current moves right in wire.
electromagnetic induction.
Uses for Electromagnetic
Induction
 Generators produce AC current
for home and industrial use.
Water, wind, or steam are
used to move large
electromagnets through the
coils of wire to produce
current.
 Transformers are used to step
up voltage of electricity that
must travel long distances
through wires. Other
transformers then step down
the voltage before it enters
our homes.