Transcript Electric potential energy

Static Electricity
 Static electricity: electric charge that can be
collected and held in one place (static means
not moving/changing).
 Static electricity is different from current
electricity. Current electricity is the
continuous flow of charge in a complete
circuit.
 In static electricity, electrons build up in one
place. A current is a pathway through which
electrons can travel.
Review from Unit 1
 Remember from unit 1, in
an atom consists of
protons (+1), neutrons (o)
and electrons (-1).
 Protons and neutrons are
in the nucleus of the atom
and cannot be changed or
moved.
 Electrons are in energy
levels around the atom
and can be taken away by
other atoms, or added to
by electrons from other
atoms.
Uses & Dangers of Static
Electricity
 Using pages 233 & 234 in your textbook, as well
as your own common knowledge, list 10 uses
and dangers of static electricity in your
notebook.
Uses/Dangers of Static
Electricity
Uses
1.
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8.
Used in paint on cars
Used to decrease air pollution
(removes smoke particles from
chimneys; air ionizers)
Helps sandwich wrap cling
Packing peanuts stick together
with static electricity
Helps blankets stick to you at
night
Sticking balloons to walls at
birthday parties
Fun – Van der Graff generator
Swiffer cloths
Dangers
1. Anywhere oxygen tanks
are used in an enclosed
space, can cause
explosions (spark)
2. Sparking around fuel
tanks can cause
explosions (that’s why
they have grounded fuel
hoses)
3. Lightning
Types of Charges
 Atoms or objects have a positive charge when
they have more protons than they do electrons.
Atoms/objects have a positive charge when
they LOSE electrons to another atom/object.
 Atoms/objects have a negative charge when
they have more electrons than they do protons.
Atoms/objects have a negative charge when
they GAIN electrons from other atoms/objects.
 Atoms/objects have a neutral charge when they
have the same number of protons as electrons.
Charges in objects can change...
 Neutral objects can develop a positive charge
when they lose electrons to other objects.
 Neutral objects can develop a negative charge
when they gain electrons from other objects.
 Positively charged objects can become
neutral when they gain electrons from other
objects.
 Negatively charged objects can become
neutral when they lose electrons to other
objects.
Electrical Discharge
 Electrical discharge is the flow of
electricity through a liquid, solid, or gas.
The flow of electricity is the flow of
electrons.
 When you get a static shock, electrons
move from the place where they have
built up (the static charge) and flow
from that place to your body.
Laws of Static Electricity
1. Like charges repel (positive pushes away
positive, negative pushes away negative)
2. Opposite charges attract (positive attracts
negative and vice versa)
3. Neutral objects are attracted to charged
objects.
Laws of Static Electricity...
 When you rub a balloon on
your head, you add electrons
from your hair to the balloon,
making it negatively charged.
 Two negatively charged
balloons will repel each other.
 When you put a negatively
charged balloon on a wall, the
positive charge of the wall
moves towards the outside of
the wall (opposite charges
attract each other). This
attraction keeps the balloon
stuck to the wall.
Visualizing Charge Transfer
– Page 231.
In your notebooks,
follow steps 1 to 8
in activity 7-1B.
Electric Force and Charge
 Electric force is the push or pull between charged
objects. Electrical force is an action-at-a-distance
force – it can apply force to an object without
touching it.
 When you touch a negatively charged object to a
neutrally charged rod, electrons get added to the rod,
making it negatively charged. Charging a neutral
object by touching it to a charged object is called
charging by conduction.
 Touching the neutral rod with a positively charged
object would have the same effect. Electrons in the
neutrally charged rod will be attracted to the
positively charged object . The neutral rod will lose
electrons and have a positive charge.
Charging by Induction
 If you bring a negatively charged object near, but not
touching, a neutral rod, the negative charge will repel the
electrons in the rod. The electrons will move down and
away from the negatively charged object, and the top will
be positively charged. This is called charging by induction.
When you move the negatively charged object away, the
charges will balance again.
 When an object is charged by induction , no electrons get
transferred from one object to the next. A change in the
position of the electrons inside the object is induced.
 Charging by induction explains the third law of static
electricity (neutral objects attract charged objects –
remember the example of the balloon and the wall).
In your notebooks…
 Using pages 233, 234 and 241 in your
textbook, explain how the following three
technologies work. Make sure to include
static electricity in your descriptions.
Lightning Rod
2. Photocopier
3. Electrostatic air cleaner
1.
 List three careers that relate to electricity.
Pages 246 & 247
Answer questions
1 to 9, 11 to 22,
25 & 26.
Energy… Some Definitions
 Energy, in science, is the ability to do work.
 Work is force acted through a distance. If you
haven’t changed places (distance) you
haven’t done any work.
 Electrical work is the work done on a charged
particle in an electric field.
 An electric field surrounds a charged particle,
and exerts a force on another electrically
charged object.
Potential Energy
 Potential energy is stored energy. When you
are not moving, you have potential energy
(the potential to start moving). When you
start moving, your potential energy is
converted to kinetic energy (the energy of
movement). Think of a mousetrap.
 Electric potential energy is energy stored in
electrons… the electrons have stored energy
and the ability to do work.
Batteries
 Batteries use electric potential energy. The
battery must be connected to a device for the
electrons to lose their stored energy. If you
connect a battery to a light bulb, for example,
the electric potential energy gets moved
through the wire inside the bulb and gets
converted to heat and light energy.
 Potential energy, electric or otherwise,
always gets converted to another form of
energy.
Electric Potential Difference
 Electric charge is measured in coulombs (C). One
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coulomb is the amount of charge passing a point in
one second when one ampere of current is flowing.
The current is the amount of charge passing a point
in a conductor every second.
A conductor is any material that allows electrons to
flow freely through it.
An ampere (A) is a unit for measuring electric
current.
The amount of electric potential energy per 1
coulomb of charge is the electric potential difference
(or just potential difference). This is also called the
voltage, and is measured in volts (V).
Electrochemical Cells
 Electrochemical cells are also called
batteries. They convert chemical energy into
electrical energy stored in charges.
 Chemical energy separates the +ve and –ve
charges – this is why batteries have +ve and
–ve ends.
 A basic battery consists of:
 Two electrodes &
 An electrolyte (either a wet paste or a solution)
Batteries continued…
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Electrodes are usually metals, but can be a
metal and another material.
The electrolyte is a substance that
conducts electricity.
In this example, the electrolyte attacks
the zinc electrode and pulls atoms off of
it.
The zinc atoms leave behind electrons on
the electrode, and it become -vely
charged.
The electrolyte also pulls electrons off
the copper electrode. This means that it
will become +vely charged.
The difference in charges creates a
potential difference (voltage) between
the two electrodes.
The amount of voltage produced depends
on the types of metal and the electrolyte
used. Most electrochemical cells produce
1.5V or 2.0V. A 12V car battery would have
six 2.0V cells or eight 1.5V cells connected
together with wires.
Questions page 259
Answer questions
1 to 8
Electric Circuits
 Electric circuits are complete pathways that
allow electrons to flow. In a circuit, electric
potential energy is transformed into other
forms of energy.
 We have already learned that current electricity
is the flow of charged particles in a complete
circuit.
 An ammeter Is a device used to measure current.
 To have a continuous flow of charge, a circuit
must contain at least one source of voltage.
Electric Circuits
Electric Circuits
There are four basic parts to an electric circuit:
1. The source : the source of the electrical energy. The
source provides electric potential energy to be used
by the other elements of the circuit. This creates a
potential or voltage drop (i.e. the sources starts
getting used up). This could be a cell, a battery, or a
generator.
2. The conductor: the wire that the electric current
flows through.
3. The load: a device that transforms the electrical
energy into other forms of energy (a light bulb, a
buzzer, a heater, a motor).
4. The switch: a device that can turn the circuit on or
off by closing or opening the circuit.
Circuit Diagrams
 Circuit diagrams are simple drawings that
demonstrate the different components of a
circuit. To draw them we use the following
symbols:
ammeter
Circuit diagrams
 Some notes on circuit diagrams….
 Ammeters are always connected in series.
This means they will be in the same line as
the source and load.
 Voltmeters are always connected in parallel.
This means that they will be draw in a
separate box or triangle connected to the
series.