Download The Electrical Nature of Matter

Science 90: Chapter 9 – Electrostatics Notes
The Electrical Nature of Matter
• There are 2 types of electrical charges: ___________________________
• The study of __________ electric charge is called ___________________.
• We will look at current electricity in chapter 10.
Electric Charge
• There are two kinds of electric charge_____________________________.
• A substance that is has no charge is called ________________________.
• When 2 neutral substances are _________________; one substance
becomes positively charged and the other negatively charged.
• ____________objects attract ________ objects including liquids and gases.
• Objects with _____________________________.
• Objects with _____________________________________ each other.
• This constancy of behaviour is called the __________________________.
• In some atoms, __________________ transfer easily from one type of
substance to another.
• In most elements, the # of _____________equal the # of _________ thus
the substance is ______________________.
• When a substance loses _____________, there are more _____________
charged protons than ______________ charged electrons thus the
substance becomes __________________ charged.
• The opposite is also true.
• When a substance gains ____________, there are more negatively charged
electrons than positively charged protons thus the substance becomes
__________________ charged.
• Objects become neutral again when they transfer these extra electrons to a
positively charged object.
Charging by Friction
• There are 3 ways that charges can be transferred from neutral objects:
_________________________________________.
• Charging by friction involves 2 substances ___________________ and
transferring ______________________ from one object to another.
• Charging in this way has many of the same effects as _________________.
• Different substances hold onto their electrons better than others.
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Science 90: Chapter 9 – Electrostatics Notes
• You can determine what kind of charge an object will obtain when rubbed
with a substance by using a list like the one in Table 1 on page 275.
• This is called an ____________________________________.
Transferring charges by contact
• Transferring a charge by friction is hard to avoid.
• When charging by contact occurs, one object is already charged, and the
other may or not be charged.
• The important factor is that there must be a _____________ between the 2
objects. The charges transfer in order to try and make them neutral again.
• This transfer of charges by contact is called _________________.
• The shock that occurs during this transfer may be painful due to the very
rapid transfer of these electric charges.
Insulators & Conductors
• An electrical ______________ is a substance in which electrons cannot
move freely from atom to atom.
• Insulators can build up an electrical charge but will hold onto that charge
until they are removed by a substance that __________________________
• _________________ are insulators that behave this way. This is why dust
particles are attracted to them and stick to these surfaces.
Insulators
• Insulators are very useful substances.
• Since electric charges ___________________________ they are used to
protect us from ___________________________.
• If electrical wires and appliances were not covered with insulators, they
would be extremely dangerous.
Conductors
• No matter how hard you polish a metal surface, it will never build up a
static charge.
• This is because it is a conductor.
• A conductor is a substance in which ______________________________
_______________________________________________________.
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Science 90: Chapter 9 – Electrostatics Notes
• If a conductor becomes negatively charged, the extra electrons move freely
along the conductor and eventually these charges are lost.
Discharging
• The process by which the extra charges on an object are transferred to
another object is called ________________________.
• The easiest way to discharge an object is to connect it to ______________
____________________________________________________________.
• When a charged object is connected or __________________, it shares its
charge with the whole Earth.
• The Earth is so large that is will take all the excess charge from an object.
• Some objects cannot be practically discharged by a wire connected to the
Earth, such as a plane or a car.
• These types of objects are ________________________.
• Planes have “wicks” on their wings to safely channel the excess charges
_______________________________________.
Induction
• This is the third way in which an object can become charged.
• The other 2 types of charging involve the transfer of charges by
________________________
• Induction involves the movement of charges _______________________.
• When a neutral particle approaches a charged object, _________________
____________________________________________________________
• This is why dust particles are attracted to and stick to a TV screen or
computer monitor.
• This is called ______________________________________.
• This is why ________________ are attracted to _____________________.
Lightning
• Lightning is a huge buildup of __________________________ in a cloud.
• These charges build up in the clouds and as these large thunderstorms pass
over objects, they attract ___________________ particles from the ground.
• Lightning typically strikes tall objects because they are the _____________
______________________________________________________
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Science 90: Chapter 9 – Electrostatics Notes
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Science 90: Chapter 9 – Electrostatics Notes
Electricity and Electric Circuits
• The movement of electric charges from one place to another is
called an ________________________.
• Electric current can be controlled. We do this by using an ______
_______________________.
Parts of an Electric Circuit
1. ________________________ – can come from a battery, a solar
cell, a plug which gets it power from a generating station, etc.
2. ___________________: This is the name given to anything that
converts electrical energy into whatever form of energy we need.
3. ______________________________: This is simply the part of
the circuit that controls the flow of current through the circuit.
This includes switches, timers, etc.
4. _____________________: These are the substances or wires that
carry the electricity through the circuit.
• The words that are used to describe a circuit can be confusing.
• A _______________ is one where the electricity is flowing
through it powering the devices connected to it. Power switch is
turned _____________.
• An __________________ is when there is no electricity is
running through the circuit. Power switch is turned __________.
Drawing an Electric Circuit
• Electric circuits are often drawn in ________________________.
(Fig. 2 pg. 300).
• In these diagrams, the _____________________ are often drawn
as ________________ with ______________________________.
• This can make very complicated circuits easier to understand.
Symbols for Circuit Diagrams
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Science 90: Chapter 9 – Electrostatics Notes
Circuit Diagram Example
Electric Potential (Voltage)
• Even when a battery is not connected to an electric circuit, the
___________ at the __________________ have ______________
___________________________.
• The instant the battery is connected to a circuit, a ______________
reaction occurs and the stored energy from this reaction exerts a
force on the ___________________ and pushes a certain number
of them onto the ________________________________.
• Electrons build up on the ____________________ and a matching
number of positive charges build up on the __________________.
• Electrons can be released with their electric potential energy from
the cell when the switch in the circuit is _________________.
• The ________________ flow through the circuit and return to the
_________________ of the cell. These __________ must return
to the cell for any further _________ reactions to occur in the cell.
• There must be a ________________________ flowing through the
circuit for any electricity to be produced.
• As the __________________ move through the circuit they release
their energy to the ___________________.
• The energy each electron has is called the _________________ of
the electron.
• This is commonly referred to as _____________________.
• The SI unit used to measure electric potential is the ___________.
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Science 90: Chapter 9 – Electrostatics Notes
• Voltage is measured by a device called a ___________________.
• The higher the voltage, the more __________________________
____________________________________________.
Electrochemical Cells
• Electrochemical cells are commonly called ___________.
• There are 2 types of electrochemical cells: ___________________
_____________________________________________________
• There are 2 types of primary cells; _________________________.
The Wet Cell
• The first wet cell was invented by Alessandro Volta in 1800.
• The wet cell is also called a __________________ cell.
• It is called a wet cell because it is made of ___________________
________________________.
• The metal parts are called the ___________________ and the
liquid is called an ____________________________.
• The metals are usually _________________________ but other
metals can be used.
• An ________________ is any liquid that ____________________.
The liquid is typically an ____________.
• The zinc in the cell _______________________________, and the
energy released separates ________________ from the zinc atoms.
• These __________________collect on the zinc plate, which is
called the _____________________ terminal.
• At the same time, ______________________ collect on the copper
plate which is called the __________________ terminal.
• These charges remain ________________ until they are connected
to an electric circuit.
• The 2 major disadvantages of a wet cell are the danger of spilling
the electrolyte and the continual need to replace the zinc electrode
and the electrolyte.
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Science 90: Chapter 9 – Electrostatics Notes
The Dry Cell
• The dry cell works very much like the wet cell except the
electrolyte is a ___________________ instead of a liquid.
• When most of the ___________________ has been used up by the
chemical reaction, the electrons _______________ and the cell is
discharged.
• Electrons flow out through the ________________ of the battery,
through the device and back into the ____________ of the battery.
• These are the typical alkaline batteries and often use ___________
____________________________________________________.
• Over time, even dry cells that have never been used will discharge.
Secondary Cells
• These are ________________________ batteries.
• It is called a secondary cell because there are ________________
_______________________; one ________________ the cell and
the other ____________________ the cell.
• Eg.
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Science 90: Chapter 9 – Electrostatics Notes
Cells in Series and Parallel
• Circuits can be connected in one of 2 ways; __________________.
• A dry cell can only achieve a maximum voltage of about _______.
If we want to achieve higher voltage we have to connect many dry
cells together.
• A 9 volt battery has six miniature dry cells in them.
• As we connect the dry cells together ______________, the voltage
_____________________________________________________.
Parallel Cells
• This arrangement of cells is used to provide _________________
_____________________________________________________.
• This is common in calculators and watches.
• We connect 2 cells _______________________, and connect the
positive terminals and the negative terminals together.
• This will provide ______________________ to the device but the
electric potential will be the same as though only one cell was
present.
Electric Current
• Shocks from static electricity are common and are an annoyance,
but getting shocked from and electric current in circuits is another
matter.
• Many people die from electrocution every year.
• Electric current is made up of _____________________________.
• In solids it is only the ________________that move through the
circuit, the _________________________________ do not move.
• Electric current is a measure of ___________________________
_____________________________________________________.
• The metric SI unit that is used to measure current is the _________
• Current is measured using an _____________________.
• A surprisingly small amount of current is lethal. 0.050 A of
current will kill a person.
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Science 90: Chapter 9 – Electrostatics Notes
• A 100 W light bulb has enough current running through it to kill
50 people.
Electrical Resistance
• This is a process which makes many of our electrical devices safe
to use.
• The molecules of all types of conductors ____________________
the flow of electrons to some extent.
• This ability to impede the flow of electrons in conductors is called
_______________________________.
• There are types of devices called __________ that are built into
many electrical circuits that intentional slow down the flow of
electrons. This decreases the ____________________ running
through the device.
• When electrons flow through a conductor, the electrical resistance
causes a loss of ___________________________________.
• This difference or loss in the amount of electric potential the
electrons have flowing through the conductor is called _________
_________________________.
• In 1827, a German scientist Georg Ohm discovered a special
relationship that exists between the potential difference across a
conductor and the electric current that flows through it. This is
now called ____________________________.
Ohm’s Law
• Ohm’s Law states that: The potential difference between 2 points
on a conductor is proportional (directly related) to the electric
current flowing through the conductor.
• This describes the __________________ caused by resistance of
the conductor.
• _________________ = _______________ x _________________
_____________
______________________________
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Science 90: Chapter 9 – Electrostatics Notes
• Potential difference is measured in ______________, Current in
___________________, & Resistance in ________________
Sample Problems
• What is the voltage drop across a tungsten filament in a 100 W
light bulb? The resistance of the filament is 144 Ω and a current
of 0.833 A is flowing through it?
•
The voltage in a computer is 120V and the current is 20 A.
Calculate the resistance.
•
Calculate the current running through a welder that is connected
to a 220 V plug and has a resistance of 28 Ω.
Types of Electric Circuits
• There are 2 types of circuits: _____________________________.
Series Circuits:
• Have you ever had a string of Christmas lights that when you
removed one bulb or a bulb burned out the whole string of lights
stops working?
• This is because these lights are in a series circuit.
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Science 90: Chapter 9 – Electrostatics Notes
• A series circuit has the current flowing on ___________________
in the circuit.
Drawing a Series Circuit
• Series circuits can have only one load or several loads connected to it.
• Example of a series circuit with 1 load:
• Example of a series circuit with 2 loads:
• In a series circuit, the resistance of the loads connected to it
_______________________ each other. Example: (See above)
The Parallel Circuit
• In this circuit, the current has _____________________________
to travel to ____________________ on the circuit.
• Each of these circuits to the loads is called a _________________.
• Because each load is connected to its own branch circuit, it does
not affect the other loads.
• This means that if you remove on bulb from the string of
Christmas lights, the rest will still stay lit.
• Example of a parallel circuit with 2 lamps:
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Science 90: Chapter 9 – Electrostatics Notes
• Notice now that the current can now flow through 2 different paths
or branch circuits.
• The 2 bulbs are identical, because the voltage drop is the same for
both. (9 V)
• The same current of 1 A will flow through each bulb, so the
current that will now be leaving the negative terminal will be 2A.
• What happens if we add a third bulb?
• If we now disconnect any bulb, the others will stay lit since the
pathway of current is not interrupted.
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Science 90: Chapter 9 – Electrostatics Notes
11.2 – Measuring Electrical Energy
• How long a battery can last depends on the amount of __________
______________ that the battery can release to operate a device.
• Energy is defined as __________________________.
• Electrical energy is the ___________________ to an ___________
by _____________________________.
• The symbol for electric energy is _____, and it is measured by the
SI unit __________________.
• One Joule represents a very small amount of energy.
• For example; One joule would power a 100 W light bulb for only a
hundredth of a second.
• Since the joule is so small, energy is often measured in ________
___________________________.
Calculating the amount of electrical energy
• _____________________________________________________
• This can be written by using the following symbols:
• _______________________________________
• ____ = _________________________________
• ____ = _________________________________
• ____ = _________________________________
• ____ = _________________________________
• Energy can be measured in _____________. Thus if you use ____
as time in your equation the units will be ___. If you use _______,
the units will be in ________.
Sample Questions:
•
•
Calculate the energy released from a battery that has been switched on for 4.5 hours, in which the
voltage drop was 6V and the current was 0.35 A.
How much energy is used by a light bulb that has been turned on for 120 minutes, has a resistance 6
Ω and a current of 0.35 A running through it.
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Science 90: Chapter 9 – Electrostatics Notes
11.4 - Rate at Which Energy Is Used
• Electrical Power is a measure of the ________________________
___________________________________________.
• The symbol for electrical power is ___, and it is measured in ____
• Power for appliances is often measured in ________________ in
order to make it easier to understand. 1 kW = _____________W
Calculating Electrical Power
• Electrical power is calculated by using the amount of __________
___________________________________________.
Electrical Power =
In symbols, this formula is:
• The above formula is rarely used in practice because you have to
measure both the energy and the time interval to be able to solve
the formula.
• The formula below is the one typically used since we already
know how to calculate voltage and current.
• ____________________________
Sample Problems
Calculate the power of a vacuum cleaner if the operating voltage is 120 V, and the current flowing
through it is 7.90 A.
Calculate the power used by a toaster if the current running through it is 4.8 A and its resistance is 3 Ω.
What is the voltage used by a mp3 player that uses 0.007 kW and has 5.3 mA running through it?
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Science 90: Chapter 9 – Electrostatics Notes
12.2 Distributing Electricity Safely
• There are 3 wires that run from the power pole to the back of your house.
2 Live wires and one neutral wire.
• The neutral wire _______________________; it is connected to the
____________ through the plumbing or by a metal stake.
• The live wires go through the ________________ on the back of the house
before it enters the home.
• It then runs through a _________________ and into the ______________.
• After the ___________________________, the power is wired into several
_______________ before it runs to the outlets and switches in your house.
• This is for ______________. Only a certain number of plugs and switches
are connected to each circuit.
• Each circuit in the house is a _____________ circuit. This is to reduce the
chance of _____________________________________.
• A circuit breaker controls the amount of ______________ running through
the circuit. If too much runs through the circuit then it will ____________
_____________________________________.
• The basic circuit breaker consists of a _____________, connected to either
a _______________________________.
• The electricity ________________________ the electromagnet
• ________________ boosts the electromagnet's magnetic force. When the
current jumps to unsafe levels, the electromagnet is ___________________
______________ connected to the switch. This causes the contacts to ____
_____________________, the switch turns off and the electricity shuts off.
• With a bimetallic strip in the breaker, the increasing current running
through it causes it to ____________________. If it heats up too much, a
spring in the breaker is then able to pull the switch into the off position.
• A ___________ is a very simple circuit breaker that can only be used until
it is _________. Once it has been blown, it must be __________________.
• A fuse is just a __________, enclosed in a casing that plugs into the circuit.
When a circuit is __________, all charge __________________________.
• The fuse is designed to _________________ when it _________________
_________________ -- if the current climbs too high, it ______________.
• Destroying the fuse ____________________ before the _______________
can damage the building wiring.
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Science 90: Chapter 9 – Electrostatics Notes
12.5 – Electrical Energy Use in the Home
• Electrical energy use in the home is measured in _____________________
• We can rearrange the formula we used in Ch. 11 to calculate the energy
that a house or appliance uses.
• Since ________________ and __________________ we can calculate
energy by using the following formula: _______________________
• _____________________
• _____________________
• _____________________
• We can also calculate the cost of the electrical energy that is used.
• ___________________________________________________
• _______________________
Sample Problems
• How many kWh of electrical energy are used in one month by a clothes
dryer that has a power rating of 5 kW and is operated for 4.5 hours a week?
• Calculate the cost of the electricity needed to operate a refrigerator for one
month if it uses 75 kWh of energy. The rate charged for electricity is
$0.08/kWh.
12.6 Reading a Power Meter
• Stand directly in front of the meter so that you can clearly see the location
of each pointer.
• If the pointer is between two numbers, read the number the pointer has just
passed, always the lowest number.
• If the pointer is between 9 and 0, always read 9.
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Science 90: Chapter 9 – Electrostatics Notes
• If the pointer appears to be exactly on a number, read the next lowest
number unless the pointer to its right has passed zero. Since the first dial
has no dial to its right, the number must be read independently.
What is the reading of the example electric meter shown below?
•
•
•
•
•
•
The pointer on the far left dial has passed 8, and is between 8 and 9. Read
the ___________ number which the pointer ____________, which is ___.
The pointer on the next dial looks like it is _______________. But, the
dial to its _____________________. So, you would read this dial as ___.
The next dial has ________________, and is between _______________.
Again, read the ____________ number which the pointer has _________,
which is ____.
The second pointer from the right has _______________, and is between
_________________. Read this as _____.
The pointer on the far right is ____________________. Read this as ___.
The answer is _______________.
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