Transcript Electricity & Magnetism

Electricity & Magnetism
Static, Currents, Circuits
Part 1: Slides 1 - 29
The world is filled with electrical
charges:
+
-
+ +
+
+ +
+
+
+
+
2
What is this electrical potential
called?
https://phet.colorado.edu/sims/html/balloons-andstatic-electricity/latest/balloons-and-staticelectricity_en.html
-
-
- -
+
++
++
3
Static Electricity
 The
build up of an electric charge
on the surface of an object.
 The charge builds up but does not
flow.
 Static electricity is potential
energy. It does not move. It is
stored.
4
Static Discharge…
 Occurs
when there is a loss of
static electricity due to three
possible things:
– rubbing (direct contact)
Conduction – direct contact
Induction – through an electrical
field (not direct contact)
Friction
5
Conductors & Insulators
Conductors vs. Insulators
– material through
which electric current flows easily.
 Conductors
– materials through
which electric current does not
flow easily.
 Insulators
7
Conductors vs. Insulators
– material through
which electric current flows easily.
 Conductors


Conductor – makes music “flow” from the orchestra
Conductor – makes train “flow” smoothly down tracks
– materials through
which electric current cannot
move.
 Insulators
8
Examples
 Conductors:
 Insulators:
 Metal
 Styrofoam
 Water
 Rubber
 Plastic
 Paper
9
• SEMICONDUCTORS
• Semiconductors are materials that can be
made to act as a conductors, or an
insulators, or something in between.
• Common elements such as carbon,
silicon, and germanium are
semiconductors.
• Can you find them on the Periodic Table? What do they have in common?
• Silicon is the best and most widely used
semiconductor.
10
Calculating Electricity
 Current
 Voltage
 Resistance
 Watts
 Amps
 Ideal
Conductors
 Ohms
 Electric bills
11
Electricity that moves…
 Current:
The flow of electrons
from one place to another.
 Measured in amperes (amps) but
it is often written as I for ideal
conductor
 Kinetic energy
12
What is Resistance?
 The
opposition to the flow of an
electric current, produces heat.
 The greater the resistance, the
less current gets through.
 Good conductors have low
resistance.
 Measured in ohms (Ω – omega)
13
What Influences Resistance?
of wire – aluminum and
copper have low resistance
 Thickness – the thicker the wire the
lower the resistance
 Length – shorter wire has lower
resistance
 Temperature – lower temperature has
lower resistance
 Material
14
What is Voltage?
 The
measure of energy given to
the charge flowing in a circuit.
 The greater the voltage, the
greater the force or “pressure”
that drives the current through the
circuit.
15
Difference b/t Volts, Amps, & Ohms
 Example
– you could say that…
 Current
(amps) measure how much water
comes out of a water pipe. (amount)
 Voltage (volts) measure how much
pressure is behind the water. (force)
 Resistance (ohms) measures the friction
against the inside of the water pipe
16
17
Ohm’s Law
 Resistance
 Ohms
= Voltage / Current
= Volts / Amps
Ω=V/I
18
Practice with Ohm’s Law
Ohms
4
15
2
9
6
Volts
100
150
30
45
48
Amps
25
10
15
5
8
19
Electric Power
Remember, P = w / t and is measured in watts.
Electric power is also measured in watts
Watts = volts x amps
Kilowatt hours –
The amount of money
you owe for the
electricity you use.
20
Difference b/t volts & watts
If
volts x amps = watts
Then
force of electricity
x amount of electricity
how powerful it is
P = _w
t
how much water?
how much time?
21
Circuits
How do batteries work?
Series circuit, DC current
How are your electronic devices
wired?
Series or parallel circuits, AC current
How is your house wired?
Parallel circuits, AC current
22
How can we control and use
electric currents?
With circuits!
 Circuit: a path for the flow of
electrons. We use wires.
23
Electric currents flow in a circle
or circuit.
There are 2 types of circuits:
 Series
Circuit: the components
are lined up along one path. If
the circuit is broken, all
components turn off.
24
Series Circuit
25
2nd type of circuit:
Circuit – there are several
branching paths to the
components. If the circuit is
broken at any one branch, only
the components on that branch
will turn off.
 Most houses and buildings are
wired this way
 Parallel
26
Parallel Circuit
27
Diodes
Diode is a device that allows
current to flow only one direction
LED lights or
LED = Light Emitting Diode
Examples: TV remotes,
computer screens, digital clocks
flat screen TVS
28
Transistors
Transistors are
semiconductors used to amplify
electrical signals
Example: Used in a stereos,
radios, and loud speakers
29
Magnetic Fields
& Electromagnets
Part 2: Slides 30 - 45
Properties of Magnets




All magnets have two areas of strongest force, called
poles.
Each magnet has one north pole and one south pole.
Like poles repel, and opposite poles attract.
The magnetic region where you can “feel the force” is
called a magnetic field.
31
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.
Randomly arranged domains =
No magnet!
Magnetic domains lined up =
Magnet!
magnetic domain
32
The Earth is a magnet!



Magnetic lines of force around
the earth are like the field lines
around a giant bar magnet.
The magnetic north pole and
the geographic north pole are
not located in the same place!
The north pole of a compass
points to the earth’s magnetic
north pole.
33
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
2.
making a more magnetic
iron core,
3.
increasing the current
through the wire.
34
What is an electromagnet?
– a magnet made
from a current bearing coil of wire
wrapped around an iron or steel
core. (ferromagnetic core)
 Solenoid – the coiled wire that
gets wrapped around the core.
 Electromagnet
35
Magnetism to Electricity

Joseph Henry and Michael
Faraday discovered that
magnetism could also
produce electric current.
Basis of alternating current.
Current moves left in wire.

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 right in wire.
36
There are 2 types of
electromagnetic currents:
Current (DC) – Where
electrons flow in the same direction in
a wire. Example: batteries
 Direct
37
2nd type of EM current:
Alternating Current (AC) – electrons flow
in different directions in a wire
 The current in buildings and devices

38
Electromagnetic Induction
 The
process of
generating an
electric current
from the
motion of a
conductor in a
magnetic field.
39
Real-World Applications
40
What is a generator?
– a machine that
changes mechanical energy to
electrical energy
 Usually use moving magnets to
create currents in coils of wire.
 Generator
41
What is a motor?
– a device that changes
electrical energy to mechanical
energy that can do work.
 Motor
42
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.
43
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.
44
That’s It !!!!

45