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ClXB-B-ElfT
3-08
I M C T R I C I T Y
*Demonstrate and explain how static and current
electricity are alike and different
Vocabulary: discharge, circuit, circuit diagram, switch, dry cell, battery,
load, positive terminal, negative terminal
3-09
*know what a coulomb is
*Define electric current as charge per unit time
p.324329
I = Q (charge)
t (time)
Understand the concept of current (what it really is)
*Know what instrument current is measured with and
where to attach it to the circuit
*Solve current problems
Vocabulary: coulomb, current, charge, ampere (amp), ammeter
3-10
*Define voltage (electric potential difference) as the energy
per unit charge between two points along a conductor
p.330336
V= E (energy)
Q (unit of charge)
Understand the concept of voltage (what it really is)
Understand what potential difference is
*Know what instrument current is measured with and
where to attach it to the circuit
*Solve voltage problems
Vocabulary: joule, volt (joules per coulomb), potential difference, voltmeter
3-11
identify 5 sources of electrical energy and technologies
Vocabulary: chemical, thermoelectric, photoelectric, piezoelectric
3-12
*Define resistance using the particle model
"Understand the concept of resistance (what it really is)
"Understand 4 factors that affect resistance
R= V (voltage)
I (unit of charge)
Vocabulary: resistance, resistor, ohm, load, Ohm's Law
Summary Concept Map
Three-Point Approach
p.382386 +
notes
p.337342
VOCABULARY
CURRENT ELECTB1C1TY
(AND HEADINGS TO HELP YOU MAKE A CURRENT ELECTRICITY
CONCEPT MAP)
Parts of a Circuit
discharge, circuit, circuit diagram, switch dry cell, battery, load, positive terminal,
negative terminal
Current
coulomb, current, charge, ampere (amp), ammeter
Voltage
joule, volt, potential difference, voltmeter
Resistance
resistance, resistor, ohm, load, Ohm's Law
5 sources of electrical energy
chemical, thermoelectric, photoelectric, piezoelectric
Other
A
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Making Light Bulbs Glow
If negative charges can flow on a path from negative terminal to a positive terminal, we
say that we have an electric current. We will have a closed circuit.
We will see the light bulb glow. That is the electrons giving off light energy. We feel the
bulb heat up. That is the electrons giving off heat energy. The electrical energy ofthe
electrons is changed to heat and light energy.
As electrons flow through thefilamentto the bulb, heat energy and light energy are
released. The bulb is an example of a load because it resists the movement of electrons
through the circuit.
r
DAT*.
NAME)
CLASS:
S H c F S f f ^ ~ M a k i n g Light Bulbs Glow
G o a l • Apply whac you learned in the Starting Point Activit)': Making Light Bulbs Glow.
W h a t t o Do
In each of the eight diagrams below, the electric light will not work. Use the space provided to explain what is
wrong with each arrangement, then adjust each diagram so that the light will work.
Diagrams
Introduction to Current Electricity Activity
How does a socket make sure the electricity travels to the right
ptacM on the bulb?
One wire coming to the socket
attaches to a piece of metal
that connects to the threads of
the socket
The other wire connects to a
piece of metal in the socket that
connects to the bottom of the
bub.
The bottom of the socket is made of an insulating material so that
the two connections do not make a SHORT CIRCUIT.
Whydoes a lightbulb light up when an electric current flows
through it?
A current is the flow of electrons.
The filamant of a light bulb offers a lot of friction to electrons.
(Friction in electricity is called RESISTANCE. So we say the
fltament has a high resistance, compared to the wires in the
circuit)
The friction between the filament and the electrons causes
the fltament to heat up.
Th* ftomenl gels so hot that it glows.
EI.cfrkClm.te ( p . ^ - t t
M
^ t >
During your Intipdu^^
You alto discovered that die wires needed to make contact with the battery and bulb in certain places:
the battery -
the bum -
These contact points were important to create a closed path through which the electricity could flow.
Such a conductive, closed path is called a
,
You can describe a circuit in words, but it is easier to use a
diagrams use
. These
to represent each of the components, or dementi, in a circuit. The basic
symbols are shown below.
Conducting Wire
Lamp
Cell
Switch
Battery
Resistor
Notice the battery symbol is similar to that of a cell. A battery is a combination of cells.
A resistor is used to represent any device that converts electrical energy into another form of energy.
Such devices are often called
. A resistor symbol could stand for a toaster, a radio,
a lamp, a microwave, a kettle, a television - anything that resists theflowof electric charge.
Measuring Electricity
Electricity can be thought of as electrons moving. Electrons are too small to
"count" so we use
coulomb of electrons
which is 6 billion billion electrons
or the symbol
Q
We will study 3 measurements of these coulombs of electrons.
How fast?
called
How much energy?
called
How easily?
called
Current
Voltage
Resistance
or the symbol
or the symbol
or the symbol
I
using the equation
l = Q
t
R
v
using the equation
V=E
R= V
I
Q
i
;
u7t- # "tec' (i;Jto
using the equation
How do we measure a "bunch" of electrons?
6 Billion billltn electroni a
1 Negatlfe Caufomi
nvEHHmmtra | Circuit Symbols
CIRCUIT DMGfUtf SYMBOLS
conducting wire
cei
wires Joined
*>#>**y (with 3 ce»s)
•I
wires not joined
lamp
'
1
ground connector
switch
ammeter
fuse
voltmeter
* 3 # J Copnigtee
Copyright O McGrw.Hil fcW. i
P«—w <nwd m fhr p w r W , 4-
fc
•* M a i n
1.
p a r t s
o f
a
Basic
Circuit
Source of Potential (Voltage Source)
Symbol
«
1
The source of potential in a circuit can be a battery, a
thermocouple, a photocell, an electric generator, or any other
device that is capable of causing electrons to flow.
2.
Load
Symbol
/
•
S
V\A/ —•
(resistor)
The load is the device in the drcuit that uses the electric energy.
It may be a light bulb, an electrical appliance, a machine, a
motor, etc. Whatever it is, the load offers resistance to the flow
of electricity, and thus the symbol for a resistor is often used to
represent any load.
3. Conductors
Symbol
*
*
The conductors are what carry the flow of electrons from the
source to the load and back again. In almost all cases, the
conductors are wires.
4. Switch
Closed Switch (on)
Symbol
The switch controls when the load is working or not. Electricity
canflowthrough an "open circuit.* The switch is a convenient
way to open and close the drcuit. We will just connect and
disconnect wires to act as a switch in our circuits.
M e a s u r i n g
C h a r g e
Charg* depends on the number of protons or electrons
you are discussing. For example, if you fltv. an object 3
billion extra electrons, you are giving It a nsgatlvo
chargo*
(
i
In practice though. It Is not usually helpful to count
Individual electrons. It Is to tsdlous and precise (sort of {
like measuring tho distance between Canada and
Australia In millimetres). Instead, sclontlsts count largo j
groups of sloctrons called Coulombs.
j
*
One Coulomb • 0 240 000 000 000 000 000 electrons or
protons (about 0 billion billion)
i
j
!
!
We write this number using scientific notation.
1 C • 0.24 x 1 0 " electrons or protons
If tho amount of chargo Is negative, then wo aro counting
electrons.
If tho amount of chargo Is positive, then we aro counting
protons.
Wo also use a smaller unit of chargo called a micro
coulomb faC)
1 nC * 1 x 10* Coulombs
Current
The movement of charge along a conductive path is calledMM 1 1 1 '
Wh« we metjura • currei^
Using the symbol I for
,QR*
and t for time, the nttthcmifical
model tor current is:
. Q
current *
charge moving past a point
time
Charge, Q, ia measured in
Time, t, is measured ia
Current is measured in
or more commonly.
Acurreotof 1 Amp means that 1 Coulomb of charge isflowingpast a point in the circuit every second
We use an
into the drcuit in.
to measure currents in circuits. The ammeter must be connected
The currentflowingfrom the negative end ofthe battery must
connect to the _____
terminal of the ammeter. The positive end of the battery must
connect to the
_ terminal of the ammeter. A
in the circuit to limit the currentflowthrough im ammeter.
must always be present
What is a coulomb and why do we use it?
How much current exists if 245coulombs pass a point every 5 seconds?
0
If the amperage is 2.3 A. how many coulombs pass by a point in 8
seconds?
Complete the tables below
Name and akbrtvki-fcm Measured m Uiaf anrrsP Abbreviation.
Current
j
Time
I
Q*
t = '
5
2
2A
6
12
2
42
7
346
7
kr-huM.
Science, Gr. 9
Characteristics of Electricity - Measuring Electricity
r
Current & Charge Calculations Worksheet
current = charge moving past a point
time
Units: I is A (amperes)
Q is C (coulombs)
t is s (seconds)
t
1. Find the unknown quantity:
a)
I = 0.4A
Q =
t = 20s
c) I = 2 A
Q = 400 C
t= ?
b) I = ?
Q = 240 C
t = 300 s
2. Find the unknown quantity (CONVERT FIRST to seconds)
a)
l =
Q = 140 C
t = 4 min =
s
b) I = 0.3 A
Q =
t = 1.5 hours =
s
c) I = 0.9 A
Q =
t = 3 min =
s
WORD PROBLEMS
1. If there is a current of 10 amperes in a circuit for 10 minutes, what quantity of electric charge
flows in through the circuit?
2. How much current must there be in a circuit if 100 coulombs flow past a point in the circuit in 4
seconds?
3. How much time is required for 10 coulombs of charge to flow past a point if the rate of flow
(current) is 2 amperes?
)
Name:
General Science 10F
Date:
Problems Involving Electric Current
Complete the following problems on loose-leaf. Show all o f your w o r k i n g including what
y o u know, what y o u need to know, the equation that you used, the steps in solving the
equation, the units, and the final answer. Y o u should use the following equations to solve
the problems.
I = q/t
q= Ixt
18
1 coulomb o f charge is 6.25 x 1 0 electrons
1. A small portable stove is plugged into a w a l l u n i t I t is determined that 360 C o f
negative charge run past a point on the coil every minute. H o w many amperes o f
current flow pas this point i n that minute.
2. I n the above question, how many electrons pass that point every minute?
3. A n ammeter is connected to an electric kettle. It reads 12 A . H o w many coulombs o f
charge flow past a given point i n the wire i n 10 seconds?
4. A voltaic cell is producing 2.6 coulombs o f electricity every 2.0 seconds. What is the
current flowing through the ammeter?
5. A 100 watt lamp passes a current o f 0.8 amperes. H o w many coulombs o f charge
would pass a given point i n its electrical plug i n half an hour? H o w many electrons
would this represent?
6. I f there were 24 coulombs passing a section o f a conductor i n 1.6 seconds, what is the
electric current i n the conductor?
7. A microwave oven has a current o f 11.7 amperes. H o w many coulombs o f charge
would pass a given point in its electrical plug in three minutes, the time it takes to
warm up supper.
8. What are the units for current, charge, and time when dealing w i t h electric current?
9. Draw a diagram that demonstrates the movement o f charge as it flows through a wire
from one end o f a battery to another.
The Nature of Electricity
Problems Involving Electric Current
(
E l e c t r i c Potential
(
In a circuit, what causes the current to flow?
1
The answer is that the cells provide a 'push which
makes the current flow round the circuit.
The push or energy given to each electron in a circuit
is called the electric potential or Volts.
When you measure volts, you compare one location
to another. This is why you must connect the volt
meter at two points on the circuit.
Volts is calculated with the formula V=E/Q
V is the electric potential
E is the energy required in Joules (J)
Q is the amount of electrons in coulombs
Science, Gr. 9
Characteristics of Electricity - Measuring Electricity
Potential Difference Calculations Worksheet
potential difference = energy
charge
V=E
Q
Units: V is V (volts)
Q is C (coulombs)
E is J (joules)
1. Find the unknown quantity:
a)
V =?
E = 45 J
Q = 15C
b) V = 9 V
E =?
Q = 150 C
c) V = 1.5V
E = 225 J
Q =?
2. Find the unknown quantity (CONVERT FIRST to volts, joules, or coulombs)
a) V = 1000 m V =
E =?
Q = 20 C
V
b) V = ?
E = 1.25 kJ =
Q = 1500C
J
c) V = 1.21 G V =
E =?
Q = 2 000 000 C
V
WORD PROBLEMS
1. The potential difference between the two terminals on a battery is 9 volts. How much work
(energy) is required to transfer 10 coulombs of charge across the terminals?
2. Ten joules of work (energy) are required to transfer 2 coulombs of charge from X to Y. What is
the difference in potential between these two points?
3. It requires 600 joules of energy to transfer a quantity of charge between points C and D of a
circuit, which have a potential difference of 30 volts. How much charge is transferred?
General Science 10F
Name:
Date:
Voltage Problems
Complete the following problems on loose-leaf. Show all of your working including what
you know, what you need to know, the equation that you used, the steps in solving the
equation, the units, and the final answer. You should use the following equations to solve
the problems.
V = E/q
E=Vxq
1. Calculate the potential difference of an electric device that produces 30 joules of
energy and has a charge of 0.2 coulombs.
2. Calculate the potential difference of an electric device that produces the same amount
of energy as in question 1, but has a charge of 0.4 coulombs.
3. Calculate the potential difference of an electric device that produces the same amount
of energy as in question 1, but has a charge of 0.15 coulombs.
4. Based on questions 1, 2, and 3 what can you conclude about the energy produced by
an electric device, and the voltage of that device?
5. How much energy is in 5 coulombs of charge in a 12 volt battery?
6. How much energy is in 20 coulombs of charge in a 120 volt outlet?
7. How much energy is in 20 coulombs of charge in a 220 volt outlet?
8. Most outlets in your home are 120 volt outlets, however, some large appliances or
heaters may use outlets that are 220 volts. Use your answers to numbers 6 and 7 to
explain why some large appliances may be plugged in to outlets that have high
voltages.
The Nature of Electricity
An electron traveling through the wires and loads of a circuit encounters
resistance. Resistance is the HINDRANCE to the flow of charge. For an
electron, the journeyfromnegative terminal of the battery to positive
terminal ofthe battery is not a direct route. Rather, it is a zigzag path which
results from countless COLLISIONS with fixed atoms within the wire or the
load. The electrons encounter resistance - a hindrance to their movement.
)
The resistance affects how fast the electrons can move.
Variables that Affects Resistance.
Resistance to the flow of coulombs of charge in an electric circuit
* length of the wire (longer wire - more resistance because there are more
collisions)
*how wide the wire is (narrow wire - more resistance)
*what conducting material the wire is made of (silver is one of the best
conductors - silver would allow the coulombs of electrons to move with the
least resistance. Because silver is expensive, we use copper and aluminum
instead for household wiring.)
I
Science, Gr. 9
Characteristics of Electricity - Measuring Electricity
v
RI
Resistance Calculations Worksheet
resistance = potential difference
current
R =V
Units: R is 0 (ohms)
V is V (volts)
I is A (amperes)
I
1. Find the unknown quantity:
a)
I = 10 A
R = 1500 0
V =?
b) I = ?
R = 200 Q
V = 240 V
c) I = 15 A
R =?
V = 110V
2. Find the unknown quantity (CONVERT FIRST to the unit with no prefix)
a)
I=?
R = 2000 O
V = 20 mV =
V
b) I = 25 mA =
R =?
V = 110 V
A
c) I = 1 kA =
R =?
V = 50 mV =
A
V
WORD PROBLEMS
1. How much resistance does a light bulb create if it has a current of 25 mA around it in a 9 V
circuit?
2. A heating coil offers a resistance of 2.5 kO. What voltage is required so that 1.5 A of current
pass through it?
3. The human body offers a very small amount of resistance (let's say 1 m f l for argument). If a
lightning bolt (said to have 1.21 GV of potential according to a famous movie called Back to the
Future released in 1984), hits you how much current is flowing through your body.