Transcript Electricity - pams-hoey

SCI.8.3.6.1 Explain the electrical nature of matter. May use simulations.
SCI.8.3.6.3 Compare and contrast conductors and insulators. Provide examples of materials that are good conductors,
semiconductors, and insulators.
SCI.8.3.6.4 Differentiate between current and static electricity.
SCI.8.3.6.5 Describe the properties of magnets and explain the relationship between a magnetic field and an electric
current.
SCI.8.3.6.6 Compare and contrast generators and motors and how they function including induction and grounding.
SCI.8.3.6.7 Identify situations in everyday life where motors and generators are in use.
SCI.8.3.6.8 Construct and compare simple, series, and parallel circuits to determine the relationship between current,
voltage, and resistance.
SCI.8.3.6.12 Show the relationship between resistance, voltage, and amperage (Ohm’s Law) when solving simple circuit
problems.
SCI.8.1.1.18 Design an investigation to illustrate the effects of static electricity.
SCI.8.3.6.10 Create an electromagnet, explain how it works, and know the factors that affect the strength of
electromagnets.
SCI.8.3.6.11 Solve simple current problems using Ohm’s law.
NEW
Explain how diodes and transistors work.
Electric Charge

Protons and electrons both have the property of charge. Recall
that protons are positive and electrons are negative.

A force of attraction exists between things that have opposite
charges.

A force of repulsion exists between things that have same charges.
Electric Field
An electric field extends
outward through space
from every charged
particle. As things
move toward each
other the charge may
move from one object
to another.
 The electric field is
strongest near the
charged particle.

Static Electricity
Because electrons can move freely things can
become either positively or negatively charged.
Charge is only being transferred from one object to
another. This is called the Law of Conservation of
Charge.
Static electricity – is the buildup of electric charges
on an object.
Methods of Charging

Friction – when two objects are rubbed together. Example:
balloon on your hair.

Conduction – the direct contact of objects. Example:
plugging something in.


Conductors – allow electricity to go through easily

Insulators – do not allow it to move through.
Induction – the jumping of electricity from one object to
another. Example: a negatively charged rubber rod can pick
up tiny pieces of paper.
Generators and Motors

a generator converts mechanical energy into
electrical energy.

electrical motor, which converts electrical energy
into mechanical energy.

Both motors and generators run because of
something called electromagnetic induction.
Discovered by Michael Faraday, this is when a
voltage is induced by a changing magnetic field.
With electromagnetic induction, an electric current
can be produced in a coil of wire by moving a
magnet in or out of that coil, or by moving the coil
through the magnetic field. Either way, voltage is
created through motion.
Comparing Generators and
Motors

* They both rely on the principle of electromagnetic in
induction.
* The both contain coils of wire magnets or
electromagnets and they both have rotating parts.
* The AC generator will probably work as an AC motor
and the DC motor will probably work as a DC generator.
* The AC generator will turn rotational energy into
electrical energy with an alternating current (AC). That is,
the current will vary in the shape of a sine wave above
and below zero amps.
* The DC motor will turn electrical energy from a direct
current (DC) source into rotational energy.
* The AC generator may generate more than one
electrical phase. That is, it might work like more than one
generator at a time.
Electric Discharge
Electric discharge – the
loss of static electricity as
electric charges move off
an object. Sometimes
slow and quiet, or rapid
with a spark of light, shock,
or crackle of noise.
Example: lightning or a
simple static shock
Circuits

A circuit – is formed when
a wire is connected to the
terminals of a source
forming a complete path.

Electric current – the
amount of charge that
passes a given point per
unit of time.

The symbol for current is
I
Things to know…



Georg Simon Ohm established
the relationship between
electric current and potential
difference. Ex. 8 v battery vs 4 v
battery.
Resistance – R opposition to the
flow of electric charge
(example: copper low: iron
high) The unit to measure
resistance is the ohm
Ohm’s law – the current in a
wire is equal to the voltage
divided by resistance
I = V/R
Superconductor
Superconductor – low temperatures, resistance is zero.
Must be kept extremely cold.
 A phenomenon observed in several metals. When
these materials are cooled to temperatures near
absolute zero, using liquid nitrogen, they have no
electrical resistance. This means they can carry large
amounts of electrical current for long periods of time
without losing energy as heat.
 Superconducting loops of wire have been shown to
carry electrical currents for several years with no
measurable loss
Another property of a superconductor is that magnetic
fields can't penetrate it. It has implications for making
high speed, magnetically-levitated trains… kinda neat
huh…

Current direction

DC (direct current) – electrons
always flow in the same
direction. Example: batteries

AC (alternating current)
electrons move back and
forth, reversing direction
regularly. (example: current in
home changes direction
every second 120x)
Diodes

A diode allows electricity to flow in one direction
only and blocks the flow in the opposite direction.
They may be regarded as one-way valves and
they are used in various circuits, usually as a form
of protection.
Transistors

A transistor is a miniature electronic component that
can do two different jobs. It can work either as
an amplifier or a switch: When it works as an amplifier, it
takes in a tiny electric current at one end (an input
current) and produces a much bigger electric current
(an output current) at the other. In other words, it's a
kind of current booster - hearing aid

Transistors can also work as switches. A tiny electric
current flowing through one part of a transistor can
make a much bigger current flow through another part
of it. In other words, the small current switches on the
larger one. This is essentially how all computer chips
work. For example, a memory chip contains hundreds
of millions or even billions of transistors, each of which
can be switched on or off individually.
Circuits
 Electric
circuit –
consists of a source
of energy; a load;
wires, and a switch.
 Sources: battery,
thermocouple,
photocell, or electric
generator
 Load – uses the
electricity
source
switch
wire
load
Series vs Parallel

Series circuit – only one path to take; if any part goes out the whole
thing goes out. Example: old Christmas lights

Parallel circuit – separate paths. Example: circuits in homes.

Fuses – protect against too much current flow, they burn out and
can be a hassle

Circuit breakers – like fuses but do not burn out.

Take out packet & complete page 2 Electrical Currents
Series vs Parallel
Power

Electric Power – a measure of the rate at which electricity does
work or provides energy. Measured in watts.

Power = voltage x current

Energy = power x time
Electric Safety

Never handle when wet or near water

Never run wires under carpet

Never overload circuits

Repair worn out wires

Put nothing in electric sockets that does not belong

Never go by fallen wires or power lines

In lightning storms get down to the ground by crouching down and
stay away from trees.

Safest spot in a lightning storm is inside a car.