Chapter 5 electricity and magnestism

ELECTRICITY AND MAGNETISM
Chapter 5 – The Material World

 Look at the picture
on page 138-139.
 Read the information
on page 138.

Circa 585 1600
Discovery of Discovery of
magnetite, a the Earth’s
natural magnet Circa 1120
magnetic
Use of the compass fields
for navigation

1752
1785
1672 Discovery
Formulation
of the
Construction of of
electrical
a machine that Coulomb’s
nature of
generates static Law
light
electricity

1821
1820
Invention 1827
Invention
of the Formulation
of the
first of Ohm’s
electro- Law
electric
1800 magnet
motor
Invention
of the
electric
cell
(battery)

1882
Construction,
in New
York, of first 2003
electrical
distribution Construction
1986 of a a maglev
network
train in China
Discovery of a
ceramic super-
conductor

1 - WHAT IS ELECTRICITY?
Many natural phenomena are electrical in nature.
1. Nerve impulses
2. Bolts of lightening
3. Chemical reactions between atoms and molecules

Electricity is one of the main forms of energy that
powers the machines we use every day.
Electrical phenomena were discovered a long time
ago.
The property of amber to attract small objects
when it was rubbed with wool was called the
electrical effect.

Any material that can attract small objects after
being rubbed is said to be electrically charged.
Electrically charged objects can be attracted or
repelled.
Benjamin Franklin determined there were two
types of charges: negative or positive.
Electricity describes all the
phenomena caused by positive and
negative charges.

1.1 ELECTRICAL CHARGES

Protons have a positive charge.
Electrons have a negative charge.
Protons are contained in the nucleus.
Electrons are found orbiting the nucleus.
The electrons found in the outermost shell (orbit)
are the valence electrons.
Valence electrons can be transferred to other
atoms.

If an object has more electrons than protons it is
negatively charged.
If an object has more protons than electrons it is
positively charged.
The Coulomb (C) is the unit of measurement for
electric charge.
One Coulomb is equal to the charge of
6.25 X 10 18 electrons or protons.
The elementary charge is the charge carried by
a single electron or proton. It has a value of
1.602 X 10 -19 C.

ELECTRICAL FORCES OF ATTRACTION AND REPULSION

Like charges repel.
Opposites attract.
The force at work during attraction and repulsion
is the electrical force.
Electrical charges can be neither created nor
destroyed: only transferred. This is the Law of
Conservation of Charge.

1.2 CONDUCTORS AND INSULATORS
Most objects are electrically neutral.
Transferring electrons can create a charge.
Charging an object means creating an imbalance in
the charges.
Objects can be classified in three categories:
1. Conductors
2. Semi-conductors
3. Insulators

Electrolytic solutions conduct electric current.
A substance that conducts electricity when
dissolved in an aqueous solution is called an
electrolyte.
Acids, bases and salts are electrolytes when in
solution.
 Salt in distilled water!!

The role of water in electrolytic solutions.
Pure, distilled water is not an electrolyte.
The formula is H2O and this does not break into
H+ and O2- when in solution!!
Tap water has dissolved ions, such as salts and
minerals from the environment.
So tap water is often a very weak electrolyte.

A substance that does not conduct electricity
when dissolved in an aqueous solution is a
nonelectrolyte.
Organic compounds often fall into this category.
C, H, and O compounds are often indicators of
organic compounds.
Sugar is C6H12O6!!
Sugar in distilled water.

Conductors permit the flow of electrical charges
(electrons).
Metals and electrolytic solutions are conductors.
Insulators do not permit the flow of electrical
charger (electrons).
Nonmetals are usually insulators; wood, plastic,
glass, ceramic, rubber, silk, and air.
Semiconductors may be conductors or insulators,
depending on other factors.
Metaloids and carbon are semiconductors

IDENTIFYING ELECTROLYTES!!!

Acids, bases and salts conduct electricity when
dissolved into a solution.
How can we tell them apart?
By their formulas!!

SALTS
Salts are made of a metal and a nonmetal OR a
nonmetal and a group of atoms
NaCl
CaCl2
 KCl
MgCl2
KI
NH4Cl

BASES

Bases contain hydroxide (-OH) and a metal OR
hydroxide combined with NH4
NaOH
KOH
Ca(OH)2
Ba(OH)2
NH4OH

ACIDS

The formula usually begins with H
This is attached to a nonmetal or a group of atoms
HCl
H3BO3
H2SO4
HBr
H3PO4

Organic acids are acids too.
Citric acid – C5H7O5COOH
The H is added at the end of the formula

1.3 ELECTRICAL FIELDS

Electrical charges interact with each other.
Electrical forces can act on each other “at a
distance”, meaning they do not have to
contact/touch each other.
An electric field is the area of space in which the
electrical force of a charged body can act on
another charged body.

Electrical fields are invisible.
They can be represented by electric field lines.
Electric field lines show the direction of the force.
They travel from positive(+) to negative (-).
Opposites attract; likes repel.

2 STATIC ELECTRICITY

Static electricity describes all the phenomena
related to electric charges at rest.
Also called electrostatic electricity.
Electric charges in motion are called dynamic
electricity

Electrically charged particles do not remain
permanently charged.
Gradually lose their charge.
Charges do not “disappear” they are simply
transferred to other objects or to water in the air.
Transfer of charges is called electrostatic discharge.
An electrostatic charge is sometimes accompanied
by a spark. The air has been heated up!!

2.1 CHARGING AN OBJECT
There are 3 ways to charge an object:
1. By friction
2. By conduction
3. By induction

Charging by friction – rub two items together.
One will pull electrons from the other, which reults
in them having opposite charges.
Chart on page 146 –those at the top tend to gain
electrons from those lower down. Plastic
Sulphur
Gold
Nickel. copper
Hard rubber (ebonite)
Wood, yellow amber, resin
Cotton
Paper
Silk
Lead
Wool
Glass

Charging by Conduction – touching a charged
object to a neutral object.
There must be physical contact.
When the originally charged object is removed, the
newly charged object stays charged.

Charging by Induction – no touching
A charged object is brought near a neutral object.
This causes the charges on the neutral object to
separate.
It will return to a neutral charge as soon as the
charged object is removed.
If the neutral object has a conductor attached to it,
some of the moved charges will be conducted away
and then the object remains charged. Even when
the charged object is removed.

1. Which of the following is moved during
electricity?
A. Electrons
B. Protons
C. Neutrons

2.

This shows the equipment needed for
charging by:
A. Friction
B. Conduction
C. Induction

3.

This shows charging by:
A. Friction
B. Conduction
C. Induction

4.

This shows charging by:
A. Friction
B. Conduction
C. Induction

3 - DYNAMIC ELECTRICITY
 Describes all the phenomena related to electrical charges in motion

3.1 – ELECTRIC CURRENT
 This is the orderly flow of charges.
 Conventional current flows from the positive electrode to the
negative electrode

CURRENT INTENSITY - AMPS

 This is the number of charges (e-) that flow past a given
point in an electrical circuit every second.
 Simply put, the flow of electrons.
 The symbol is I
 The unit is the ampere (amp)with the symbol A.

IA = 1C
1s

 The current intensity in a circuit can be determined by the
following formula:
I= q
Δt
 I is the current intensity, (A)
 q is the charge (C)
 Δt is the time interval, (s)

 An ammeter is used to measure current intensity.
 When connecting an ammeter in a circuit it is hooked up in
series.

POTENTIAL DIFFERENCE - VOLTS

 This is the amount of energy transferred between two
points in an electric circuit.
 It is measured in volts
1V = 1 J
1C

 Potential Difference is determined using this formula:

V=E
q
 V is the potential difference,V
 E is the energy transferred in joules, J
 q is the charge, C

 A voltmeter is used to measure potential difference.
 A voltmeter is connected in parallel.

RESISTANCE

 Resistors transform electrical energy into another form of
energy
 Thermal energy - heat
 Mechanical energy – movement like turning, spinning…
 Light
 Sound

 Resistors are often included in circuits to allow the amount
of electrical energy passing through a circuit to be
controlled or reduced

 Electrical Resistance is the ability of a material to hinder
the flow of electric current.
 The factors that affect a materials ability to be a resistor
are:
1. The nature of the substance
2. The length – longer wire is a better resistor
3. Diameter – thinner wires are better resistors
4. Temperature – warmer temperature means more resistance

 A good conductor ( poor resistor) is:

SHORT, FAT, COLD AND COPPER

 Resistance (R) is measured in ohms (Ω)

1 Ω = 1V
1A

OHM’S LAW

 For a for a given resistance, the potential difference in an
electrical circuit us directly proportional to the current
intensity.
 This formula can be rearranged to find V, R and I.

3.2 ELECTRICAL POWER

 This is the amount of work an electrical device can perform
per second.
 An electrical power of one watt works at one joule per
second.
1W = 1 J
1s

 The formula for electrical power is:

PE = W
Δt
 PE is the electrical power, W (watts)
 W is the work, J (joules)
 Δt is the time interval, s (seconds)

The formula for electrical power is:

PE = W
Δt
PE is the electrical power in watts, W
W is the work, joules, J
Δt is the time interval, seconds, s

Power can also be determined by the following:

PE = VI

V is the potential difference in volts, V
I is the current intensity, amps , A

The amount of electrical energy used by a device
can be determined by multiplying it electrical
power by the time.
Electrical energy is measured in joules (J)
1 W * 1 s = 1 J/s * 1 J/s * 1 s
=1J
Kilowatt hours are also used
1 kWh = 1000 W * 3600 s = 3 600 000 J

The kilowatt hour is the unit used to calculate
consumption for electricity bills.
The following formula is used to describe the
relationship between electrical power and
electrical energy:

E = PΔt
E = electrical energy in joules (J) or kilojoules
(kJ)
P = electrical power in W or kW
t = time in s or h

Changing from joules to kilojoules:
1 J = 1000 kJ

To change from joules to kilojoules divide by 1000;
2000 J = 2 kJ
180 J = 0.18 kJ
To change from kilojoules to joules multiply by 1000;
50 kJ = 50 000 J
0.25 kJ = 250 J

Remember there are 60 seconds in one minute.
3 minutes would have…
3 * 60 = 180 s
There are 60 minutes in one hour.
60 * 60 = 3600 s in one hour
How many seconds in 2.5 hours?
60 * 60 * 2.5 = 9000 s

Example : If a 100 W amplifier runs for 30 minutes,
how energy does it consume?

Answer:
E = Pt
P = 100 W
t = 30 * 60 = 1800 s
E = 100 * 1800
= 180 000 J or 180 kJ

Since P = VI, the formula can also be written as

E = VIt
There will be occasions when this is handy.

Example:
How much energy is used in 1 hour by a motor
whose rating plate indicates 110 V and 2.0 A?

Answer:
E = VIt so…
V = 110 V
I = 2.0 A
t = 1 h = 60 * 60 = 3600 s
E = 110 * 2 * 3600
= 792000 J

3.3 ELECTRICAL CIRCUITS

For charges to flow, there must be a loop for them
to follow and they must be able to return to the
start
An electrical circuit is a network in which electrical
charges can flow continuously.
The loop must be closed with no breaks.

The lights will turn on
as long as the switch is
closed and there are
no other breaks. What
is a burned out light
bulb?
A break! In this case it
will cause the electric
current to stop and
none of the lights will
light.

All electrical circuits have three things:
1. A power supply
2. One or more elements that use electrical energy
3. Wires to carry the charges

We use symbols to represent these and in our
circuit diagrams

SERIES CIRCUITS
 The elements are connected end to end and make a single
loop.
 This means that if one of the parts of the circuit is defective,
no current will pass so nothing will work.
 Energy is used up as it passes along, so the last element may
not receive much!!!

PARALLEL CIRCUITS
A circuit that branches at least once
The current may follow different paths
If one branch has a defective component the other
branches will not be prevented from working.
The total current is divided at the branches; not
always equally.
The voltage will be
the same in each
branch

In a series circuit the number of amps is the same
at every point along the way.
It = I1 = I2 = I3 = I4…

In a series circuit the number of volts is divided
over the components using the circuit.
Vt = V1 + V2 + V3 + V4…

Since your voltage is not the same everywhere
your lights will not be equally bright!!

It=5A

I1=5A I2=5A I3=5A Vt=15A

V1= 5A V2= 5A V3= 5A
The volts only split evenly if the bulbs
are equal in resistance

In parallel circuits, voltage is equal in each branch
Vt = V1 = V2 = V3 = V4…

In parallel circuits the amps (current is divided) but
not always evenly.
It = I1 + I2 + I3 + I4…

Bulbs on different branches will have the same
brightness!!

 Power supplies are the cell
or battery
 The switch is a switch!!
 Resistor (anything that slow
current down and uses
energy – lights, motors,
actual resistors…)
 The lamp is a light bulb but
they can also be represented
by the resistor symbol

The bulbs can be represented by resistors
symbol, as well.

Draw a series circuit with the following elements: a
switch, a power supply, 2 resistors, an ammeter and
a voltmeter. The voltmeter is measuring the
voltage over one of the light bulbs.

 Draw a series circuit diagram which has the following
elements: a switch, a battery, 3 light bulbs, a resistor, an
ammeter and a voltmeter. The voltmeter is to measure the
voltage over the battery.

Draw a series circuit with 2 resistors and 2 light
bulbs, a power supply and a switch. Include an
ammeter and a voltmeter. The voltmeter is
measuring the potential difference over the two
resistors.

Draw a parallel circuit with the following elements:
one power supply, one switch, 3 light bulbs in
parallel with each other and an ammeter to
measure the current in the circuit.

Draw a parallel circuit with the following elements:
a switch, a power supply, two light bulbs, 2
ammeters and 2 voltmeters. The amps and volts
must be measured in each bulb.
Do we need two voltmeters?????

WHAT IS MAGNETISM?

A magnet is an object that can attract other
objects containing iron, cobalt and nickel.
Magnetism describes all the phenomena caused by
magnets.

MAGNETIC FORCES OF ATTRACTION AND REPULSION

All magnets have a north-seeking and a south-
seeking pole
The N-pole of a magnet is attracted to the North
pole of the Earth
This means that the magnetite north pole is really a
south pole!!!
Opposite magnetic poles attract.
Like magnetic poles repel

4.2 MAGNETIC FIELDS

This is the area of space in which the magnetic
force of a magnet can act on another magnet.
Iron, nickel or cobalt can all be made into magnets
so they are affected by the magnetic field.

Magnetic field lines go from the north pole to the
south pole.
The lines are closer together at the poles where
the force is greater

4.3 MAGNETIZING OBJECTS
A ferromagnetic substance is a substance with the
ability to acquire magnetic properties
The items must contain some iron, nickel or cobalt.
We must line up the domains!!!
Can be done with a strong magnet moving
correctly.
Can also be done using electricity, which we will
see later
A magnet can be demagnetized by a sharp hit, too
much heat, or the presence of the opposite pole

5 - ELECTROMAGNETISM

Electromagnetism describes all the phenomena
resulting from the interaction between electricity
and magnetism.

5.1 MAGNETIZATION BY ELECTRICITY

A magnetic field can be generated using dynamic
electricity.
The magnetic field will only exist when the current
flows.
The Magnetic field of a live wire:
The magnetic field lines form circles around the
wire.
Their direction depends on the current direction

THE RIGHT-HAND RULE
The thumb points in the direction of conventional
current (points to the negative pole) and the curve
of the fingers show the direction of the magnetic
field lines (point towards the south pole)

AN ASSIGNMENT TO BE DONE IN TEAMS
AND DONE IN 5 MINUTES.

Create a solenoid.
Explain, in writing, what you have done
and what you can expect from your
solenoid. Be sure to explain if the nail
is important

THE MAGNETIC FIELD OF A SOLENOID
A solenoid is a cylindrical coil of live wire.
The magnetic field of a solenoid is stronger than
the electric field of a straight conductor (straight
wire)
Again, use your right hand!!
The curved fingers point in the direction of
conventional current.
The thumb points to the north

The core used in a solenoid can make the field
stronger –soft iron cores are most effective.
The more coils the solenoid has the stronger the
field.
More current makes a stronger current too.

HOW IS A SOLENOID DIFFERENT FROM A BAR
MAGNET

The magnetic field of a solenoid can be turned on
and off
The direction of the magnetic field can be reversed
by changing the direction of the current.
The strength (intensity) can be modified by
adjusting the electric current.
The strength of a bar magnet can not be modified
at will.

These characteristics of solenoids explain why they
are used in technological applications.
And they can easily be turned into
electromagnets

5.2 CHARGING BY MAGNETISM
Can electric current be generated from a magnetic
field?
Yes!!
The magnetic field must be in motion relative to
the charge or the conductor.
Two ways to do this:
 By moving a conductor inside a magnetic field
 By moving a magnet around a conductor

Electromagnet induction means generating a
electric current in a conductor by varying a
magnetic field around the conductor.
It is used to transform mechanical energy into
electrical energy
Most electric generators work this way.
Electromagnetic induction
 Steve Spangler's Electromagnet

Chapter 5 electricity and magnestism

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