Electric Circuit: SCIENCE 8 (Physics)

Electric Circuit
SCIENCE 8 (Physics)
ELECTRICITY
Electric Field
Electrostatics Electric Charge Electric Force
Electric Potential
Electric circuit/connection Ohm’s Law

Electric
Current (I) • Electrical Power
• Electrical energy
 Electric charges
Gr. 7
 Attraction/Repulsion between charges

 Flow of charges (Simple electric circuit)
Magnetic
Field and
 Electric current (I, V, R relationship)
Gr. 8
Current
 Electrical connections (connections at home)
DEPARTMENT OF EDUCATION 2
ELECTRICITY AND MAGNETISM
Electric Field
Electrostatics Electric Charge Electric Force
Electric Potential
Electric circuit/connection Ohm’s Law

Electric
Current (I) • Electrical Power
• Electrical energy
• Magnetic Field
Magnetism • Magnetic forces
Magnetic Field (B) B due to I Electromagnets

Magnetic
Force of B on I Motors
Field and
Current
•Generator/Transformer
EM Induction Faraday’s Law •Power Transmission
DEPARTMENT OF EDUCATION
Power Generation, Transmission, and Distribution
Grade 9
Where does electricity
come from? How is it
produced? How does it
get to our home?
Source: http://www.netgainenergyadvisors.com/
G8 Force, Motion, and Energy
Electricty
Learning Competencies
❖ Infer the relationship between current and charge; (S8FE-Ih-30)
❖ Explain the advantages and disadvantages of

series and parallel connections in homes;
(S8FE-Ii-31)
❖ Differentiate electrical power and electrical energy; (S8FE-Ii-32)
❖ Explain the functions of circuit breakers,

fuses, earthing, double insulation, and other
safety devices at home. (S8FE-Ii-33)
Objectives
• Infer the relationship between current and
charge; power and energy; current-
voltage-resistance (K)
• Explain the advantages and
disadvantages of series and
parallel connections in homes (P)
• Explain the functions of circuit breakers,
fuses, earthing, double insulation, and
other safety devices in the home (P)
G8 Force, Motion, and Energy
Electricty
CONTENT
❖ Electric Current, Voltage & Resistance
❖ Ohm’s Law
❖ Electrical Connection
✓ Series Circuit
✓ Parallel Circuit
❖ Electrical Power and Electrical Energy
❖ Safety Precaution in Using Electricity
✓ Short Circuit
✓ Overload
Make your own series circuit
Make your own parallel circuit
Compare a series and a parallel circuit
PREDICT, TEST AND EXPLAIN
How will the brightness of the bulbs change as
we add more in series?
+ + +
What does this imply about the current in the

circuit?
Series circuit – 1 bulb
SERIES CIRCUIT
When electrons have
to flow through one
part to get to the next
part
More components =
more resistance
Increase resistance =
decrease current (flow)
Less current =
less bright bulbs
As voltage increases,
current increases
SERIES CIRCUIT PROS & CONS
Problems with Series:
The more devices (resistors) in a series circuit,
the less current passes through (dimmer bulbs).
If one resistor breaks (a bulb goes out) the entire

series is turned off.
SERIES CIRCUIT - RESISTANCE
Resistors – resists the flow of electrical

current
• Increased resistance will reduce the rate

at which charge flows (aka current)
• Total resistance goes UP with each

resistor since the current has must go
through each resistor.
• Total Resistance = Sum of all

resistors in the series
RT = R1+R2+ R3…
SERIES CIRCUIT - CURRENT
Current = amount of charge (flow of

electrons)
 Like the flow of water
 A current can't just disappear
(appear)
 Since only one path if some electrons
flow through R1, then they have to
continue flowing through R2 and R3.
 Since the Current is the same

through the entire circuit
IT=I1=I2=I3
SERIES CIRCUIT - VOLTAGE
Voltage is the electric equivalent of
water pressure.
The higher the voltage, the faster electrons

will flow through the conductor.
Each component has resistance that

causes a drop in voltage (reduction in
voltage).
Total Voltage = The sum of voltages across

each series resistors
VT = V1 + V2 + V3…
TO SUM IT UP…
Series
Voltage (V) VT = V1 + V2 + V3…
Current (I) IT=I1=I2=I3
Resistance
RT = R1+R2+ R3…
(R)
SERIES CIRCUIT - EXAMPLE
• Given
– Vbattery = 12 V
– R1 = 50 W, R2 = 100 W, R3 = 100 W
• Complete the following table

V I R
1
2
3
T
PREDICT, TEST AND EXPLAIN
How will the brightness of the bulbs change as
we add more in parallel?
+ + +
What does this imply about the current in the

circuit?
PARALLEL CIRCUIT PROS & CONS
Advantages
The more devices (resistors) in a parallel circuit, does
not decrease the current (does not dim bulbs).
If one resistor breaks (a bulb goes out) the rest do not.

Problems
Current doesn’t stay the same for entire circuit
So energy is used up quicker
So the total current increases = faster electrons = hotter wire = fire?
PARALLEL CIRCUIT - RESISTANCE
• Resistors added side-by-side
• The more paths, the less TOTAL
resistance.
1/ RT=1/R1+1/R2+1/R3
• Ex. 2 resistors in parallel with 4Ω
each.
• Since the circuit offers
two equal pathways for charge flow,
only 1/2 the charge will choose to
pass through a given branch.
THE TOLL GATE ANALOGY
http://www.physicsclassroom.com/class/circuits/Lesson-4/Two-Types-of-Connections
• Adding toll booths in series increases resistance and slows the

current flow.
• Adding toll booths in parallel lowers resistance and increases the
current flow.
PARRALEL CIRCUIT
PARALLEL CIRCUIT - CURRENT
ALL paths are used!
But the charge divides up into all

branches
One branch can have more current

than another branch (depends on
resistance in branch).
Total current = sum of current in each

path
IT = I1 + I2 + …
PARALLEL CIRCUIT - VOLTAGE
• A charge only passes

through a single resistor.
• Voltage drop across the
resistor that it chooses to
pass through must equal the
voltage of the battery.
• Total voltage = the voltage
across each individual
resistor
VT = V1 = V2 = …
TO SUM IT UP…
Parallel
Voltage (V) VT = V1 = V2 = …
Current (I) IT = I1 + I2 + …
Resistance
1/RT=1/R1+1/R2+1/R3
(R)
SERIES VS. PARALLEL CIRCUIT
Series Parallel
Vtot = V1 + V2 +
Voltage (V) Vtot = V1 = V2 = …
V3…
Current (I) Itot=I1=I2=I3 Itot = I1 + I2 + …
Resistance 1/Req=1/R1+1/R2+1/R3
Req = R1+R2+ R3…
(R)
Which is better? Series or Parallel?
Parallel
• Most things are wired in parallel
• Because of the fact that the more you plug in,
the intensity doesn’t decrease.
• Of course, this also increases the risk of fire
• This is why homes have fuses or circuit
breakers. They turn off everything in the
circuit when current moves too fast.
Guide Questions
a) What happened to the bulb when the exposed
parts of the wire touch momentarily?
(The light of the bulb went out/becomes dimmer)
b) How does it feel? (It feels hot/warm?)
c) What would happen if we let the exposed
wires touch for a longer period of time?
(It will become very hot.)
d) What do you call this circuit and why?
(Short circuit. Because the current takes the path of
least resistance.)
Which of these bulbs will light?
Build the circuits!
Electricity will always
A. take the easiest path.
✓ It is easier to flow through

a wire than through the
bulb.
B. So in circuits B and C the
x
electricity does not pass
through the bulb.
The cell or battery still
loses energy because ,
C. electricity is still flowing.
x This type of circuit is
known as a SHORT
CIRCUIT.
What is a short circuit?
Current will always pass along the path of least resistance.
The resistance of the wires in a circuit is low compared to the
resistance of components, such as bulbs.
If current can flow without passing through the components
in a circuit, this is called a short circuit.
The current can only pass These circuits both contain a

through the bulb. short circuit.
Circuit Protector
Fuse
A fuse is a safety device that
protects an electric cable from
overheating so that the
insulation does not catch fire.
Electronic
Symbol
How does a fuse work?
A fuse is a built-in weak point in a circuit. It contains a thin
wire with a higher resistance than normal wire.
terminals
thin wire with case made of

high resistance insulating material
When a large current flows the wire becomes hot. If too
much current flows, the wire overheats and melts, which
breaks the circuit.
Electrical Power
Electrical Power (also known as Wattage)
•is the rate at which an electric appliance converts electrical
energy to other forms. (rate of energy transfer)
•is expressed in terms of “watts”. Watt is equivalent to Joule

per second.
•is a product of the voltage and current passing through the
component.
power (W) = voltage (V) × current (A)
P = IV
We can express the relationship between current,
voltage and power mathematically using the equation:
Power = Current x Voltage
P=IV
Voltage measured in Volts (V)
Current measured in Amps (A)
Power measured in Watts (W)
Electrical Power
power (W) = voltage (V) × current (A)
What is the power of a bulb which uses a 230 V mains supply

and has a current of 0.44A passing through it?
P = V × I = 230 × 0.44 = 101.2 W
What is the voltage across a microchip if it has a normal

operating power of 0.5 W and draws a current of 0.1 A?
V = P ÷ I = 0.5 ÷ 0.1 = 5 V
Other equations for Power
Electrical power can also be calculated using resistance.
The equations linking power to resistance are found by
substituting the equation V = I × R into the power equation:
P=V×I P=V×I
and… V=I×R and… I=V÷R
Therefore, using substitution: Therefore, using substitution:

P=I×R×I P=V×V÷R
P = I2 × R P = V2 ÷ R
Power calculations
If you have a filament bulb and it has a potential
difference of 200V across it and a current of 0.2A running
through it. At what power is the bulb operating at?
P = IV
P = 0.2A x 200V
P = 40W
Power calculations
If you have a filament bulb and it operates at a power of
60W and it has a potential difference of 240V across it,
what is the current running through the bulb?
P = IV
I = P/V
I = 60W / 240V
I = 0.25A
Concept Check
Suppose you are buying a refrigerator and you have a

choice between two models with labels shown below.
Which will you take? Why?
Refrigerator A Refrigerator B
220 V 220 V
60 cycles 60 cycles
0.82 A 0.75 A
What is Electrical Energy
Electrical Energy
•The amount of electrical energy consumed by a certain
appliance can be calculated as the product of it power rating
and the duration of usage.
Electrical Energy = Power x time
•is expressed in terms of “Joules”

•It can also be expressed in Watt.hour (Wh) or kiloWatthour
(kWh)
Prove that Wh is a unit of Energy
1 Wh = (1 W) (1 hr)
= (1 J/s)(3600 s)
1 Wh = 3600 J
1 kWh = 3, 600, 000 J
What is Electrical Energy
Electrical Energy
•The amount of electrical energy consumed by a certain
appliance can be calculated as the product of it power rating
and the duration of usage.
•is expressed in terms of “Joules”

•It can also be expressed in Watt.hour (Wh) or kiloWatthour
(kWh)
Prove that Wh is a unit of Energy
1 Wh = (1 W) (1 hr)
= (1 J/s)(3600 s)
1 Wh = 3600 J
1 kWh = 3, 600, 000 J
Sample Problem
1)A 20 w table lamp is used for 10hrs. How
much energy is consumed in kWh?
2)The power rating of a light bulb when use

at 220 v is 50 W
a)How much current passes through it ?
b)How much energy is consumed in 10s ?
Sample Problem
1)A 20 w table lamp is used for 10hrs. How much
energy is consumed in kWh?
Given: P = 20 w
t = 10 hrs
E = Pt
= (20 w) (10 hrs)
= 200 Wh
200 Wh x 1 kWh = 0.20 kWh
1000 Wh
Sample Problem
2) The power rating of a light bulb when use at 220 v is 50 W
a) How much current passes through it ?
b) How much energy is consumed in 10s ?
Given: A.) B)
P= 50 w P= IV E= Pt
V= 220 v I= _P_ = (50 W)(0.0028 hrs)
t = 10 s = 0.14 Wh
= 0.0028 hrs I= 50 w V = 0.00014 kWh
220 v
I= 0. 227 A
Task: My Monthly Electrical Consumption
Household Power Rating Length of time Electrical

Appliances (W) used per day Energy
(hour) Consumed
(KWh)
Total Electrical Energy Consumed in a day

Total Electricity Cost per day ( note: 1KWh = ₱ 9.00)
Electric Bill for 1 month
Common Household Appliance
Power Rating
LED Bulb: 9 W; 12 W; 15 W Water Dispenser (with heater):

550 W
Refrigerator (small): 225 W Home Theater: 1000 W
Refrigerator (big): 300 W Flat Iron: 1000 W
Radio: 15 W Washing Machine: 500 W
LED TV: 35 W Vacuum Cleaner: 1500 W
Desk/Stand Fan: 80W Hot Plate Stove: 1200 W
Ceiling fan: 160 W Desk Top Computer: 200 W
DVD Player: 300 W Room Air Conditioner: 1000 W
Electrical Power and Electrical Energy
What do we pay for in

our Electric Bill – is it
Electrical Power or
Electrical Energy?
Electrical Power and Electrical Energy
When an electrical utility company charges a

household for the electricity that they used, they are
charging them for the electrical energy.

Unit: Watt hour (Wh)
1 Wh = 3600 J
1 kWh = 3, 600, 000 J

Once a group of 50 people
was attending a seminar.
Suddenly the speaker
stopped and decided to do a
group activity.
He started giving each one a
balloon. Each one was
asked to write his/her name
on it using a marker pen.
Then all the balloons were
collected and put in another
room.
Now these delegates were let
in that room and asked to find
the balloon which had their
name written, within 5 minutes.
Everyone was frantically
searching for their name,
colliding with each other,
pushing around others and
there was utter chaos.
At the end of 5 minutes no
one could find their own
balloon.
Now each one was asked to
randomly collect a balloon
and give it to the person
whose name was written on
it.
Within minutes everyone
had their own balloons.
More or less this is
happening in our learning
area. Everyone is looking for
the competencies he/she is
lacking, not knowing where it
is.
Our fulfillment lies in the
fulfillment of others.Help
them and you will get
yours.
AKO NA NAMAN ANG MAY
KASALANAN?
Some entries (photos, videos, quotes,
reviews, news… etc.) that appear on this
presentation were taken from different
sources and search engines (e.g. Google,
Disclaimer MSN, Yahoo) without permission but with
attribution. Much care has been taken to
acknowledge the owners/authors to copy
their materials whether it’s copyrighted
or not. The teacher gave much time &
effort to research the original
authors/writers but failed in some. Any
error or oversight that may have been
possibly made is unintentional & will be
corrected. Rectification is welcome at
jeffpee7@gmail.com.
This presentation is intended only for

Training of Teachers on Critical Content
in Science 8 Physics. Distribution of
copies of this presentation is highly
discouraged.
tsoktok.blogspot.com
Activity 1
SEE THE ATTACHED FILE
SLM_Module6_Activity Sheets
•Edited for classroom use by Sir Jaytee -

Quiz
1. Which of the following BEST describes the electron flow in a circuit?
A. the direction of electron movement

B. The total charge of the electrons
C. The rate of electron movement
D. The number of electrons
2. In a parallel circuit containing set of bulbs, if one of the bulbs blew up, what happens to the effectiveness of the resistance?
A. Remains same
B. Increase
C. Decrease
D. Fluctuate

Quiz
4. Household circuitry are prevented from overheating by means of which of the following below:
A. fuse
B. switch
C. socket
D. transformer
4. Which of the given statements below is NOT true about extension cords?
A. They are used for operating multiple electrical devices
B. Their current capacities are not specified if they are sold in the market
C. Overheating may result if the current exceeds its rating
D. None of these is true
4. You have this set of materials: cloth, rubber, water and copper. Which of these is known as a poor conductor of
electricity?
A. Rubber
B. Copper
C. Water
D. Steel


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Electric Circuit

Electric circuit/connection Ohm’s Law

 Attraction/Repulsion between charges

Electric circuit/connection Ohm’s Law

Magnetic Field (B) B due to I Electromagnets

❖ Explain the advantages and disadvantages of

❖ Explain the functions of circuit breakers,

What does this imply about the current in the

If one resistor breaks (a bulb goes out) the entire

Resistors – resists the flow of electrical

• Increased resistance will reduce the rate

• Total resistance goes UP with each

• Total Resistance = Sum of all

Current = amount of charge (flow of

 Since the Current is the same

The higher the voltage, the faster electrons

Each component has resistance that

Total Voltage = The sum of voltages across

Voltage (V) VT = V1 + V2 + V3…

Current (I) IT=I1=I2=I3

• Complete the following table

What does this imply about the current in the

If one resistor breaks (a bulb goes out) the rest do not.

• Adding toll booths in series increases resistance and slows the

But the charge divides up into all

One branch can have more current

Total current = sum of current in each

• A charge only passes

Current (I) Itot=I1=I2=I3 Itot = I1 + I2 + …

✓ It is easier to flow through

The current can only pass These circuits both contain a

thin wire with case made of

•is expressed in terms of “watts”. Watt is equivalent to Joule

power (W) = voltage (V) × current (A)

Voltage measured in Volts (V)

Current measured in Amps (A)

Power measured in Watts (W)

power (W) = voltage (V) × current (A)

What is the power of a bulb which uses a 230 V mains supply

P = V × I = 230 × 0.44 = 101.2 W

What is the voltage across a microchip if it has a normal

and… V=I×R and… I=V÷R

Therefore, using substitution: Therefore, using substitution:

Suppose you are buying a refrigerator and you have a

Electrical Energy = Power x time

•is expressed in terms of “Joules”

Electrical Energy = Power x time

•is expressed in terms of “Joules”

2)The power rating of a light bulb when use

Household Power Rating Length of time Electrical

Total Electrical Energy Consumed in a day

LED Bulb: 9 W; 12 W; 15 W Water Dispenser (with heater):

What do we pay for in

When an electrical utility company charges a

Electrical Energy = Power x time

1 kWh = 3, 600, 000 J

This presentation is intended only for

•Edited for classroom use by Sir Jaytee -

A. the direction of electron movement