Week Changes in the Motion of Objects

1
Lesson
I
In this lesson, you will learn the concepts that you can use to investigate
the relationship between the amount of force applied and the mass of the

An object may be acted upon by several forces weather object is at rest or

in motion. An object may be pushed and pulled in different directions at the
same time. For you to identify the forces which cause the change in the motion of
an object, it is important to determine all the forces acting on the object.
Examine Figure 1 below. Is there a motion? Why do you think so?

Figure 1.

Motion is a phenomenon in which an object changes its position over

time. Motion is described in terms of displacement, distance, velocity, acceler-
ation, speed and time. In the above illustration, the bus is moving from its ref-
erence point of its place of origin. THe bus moves with certain speed, at a rate
by which it accelerates at specific time. With regards to the man, there is no
motion as there is no change in his position nor displacement.
What will happen to the man as he is standing still and the bus move for-
ward? How about when the bus suddenly stops?
Dynamics is the study of forces that cause objects and systems to move.
Force is simply defines as the push or a pull of an object with a specific magni-
tude and direction. There is a need for a standard force when representing a
vector quantity (either push or pull). The push or pull on an object can vary
considerably in either magnitude or direction.

hold on to the grips handle, the force exerted by the bus through the handle

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Law of Inertia or Newton`s First Law of Motion
The illustration in Fig. 1 demonstrates the property of an object to resist
any change in its state of motion. This is known as inertia. A body at rest re-
mains at rest or, if in motion, remains in motion at constant velocity unless act-
ed on by a net external force. All objects have the tendency to resist changes in
their state of motion or keep doing what the objects are doing. However, chang-

has more inertia is more difficult to move from rest, slow down, speed up or
change its direction. This is illustrated in fig. 1 that when the bus suddenly
stops, then there will be change in motion. Inertia is exhibited when the body
moves forward as if to continue moving. Sudden acceleration will make the body
moves backward. Have you experienced this kind of motion when riding a bicy-
cle or in a jeepney?

Learning Task No. 1: Fill in the box the correct letter (s) being described in
each item. Write your answer in your notebook.

1. The scientist who formulated the laws of motion.

W N

2. The force needed to stop an object in motion is called?

R C I N

3. The property of an object that resists change in its state of motion.

E A

4. The sum of all the forces acting on the object is zero, which is the first
condition of it and it has two forms.
E I B M

5. The body will remain at rest or move at constant velocity unless acted
upon by an external net force r unbalanced force.
W O F N T

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Law of Acceleration: Newton`s Second Law of Motion
Study Figure 3 showing acceleration of a large mass of object . The mov-
ing truck accelerates at a speed lower than smaller object with smaller mass.

not balanced or if the external net force is not zero. In the presence of a net
force, the object will accelerate (unbalanced force)

acceleration of an object as produced by a net force is directly proportional to

the magnitude of the net force, in the same direction as the net force and in-
versely proportional to the mass of the object.
The second law states that the acceleration of an object is dependent up-
on two variables: the net force acting upon on the object and the mass of the ob-
ject. So the acceleration of an object depends directly upon the net force acting
upon the object, and inversely upon the mass of the object. As the net increases,
so the objects acceleration also increases.

F a
Figure 2. The Law of Acceleration showing the effect of mass of an object to tis accelera-
tion (Source: Marc Aller Anthony M. Guevarra, San Bartolome National High School,, RTOT 2018 )

Acceleration is INVERSELY related to the mass of an object.

In other words, if the object has large mass, there is small acceleration while
small mass of moving object has larger or faster acceleration of moving objects

Large Mass Small acceleration

F a

Small Mass F a Larger acceleration

(Source: Marc Aller Anthony M. Guevarra, San Bartolome National High School, RTOT 2018)

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 Like any other quantity, force has unit and is expressed in Newton (N).
One Newton is defined as the amount of force required to give a 1kg mass an
acceleration of 1m/s/s, or 1Newton (N) = 1kg/m². It is also the acceleration of
any object due to gravity.
Force is measured by the multiplying the mass of an object to its acceler-
ation. The formula is written as:
f= m x a f= force m=mass of an object a= acceleration
Sample Mathematical Problem :
Suppose a grocery cart has a mass of 0.45kg is push with a force of 90N.
What will be the acceleration of the grocery cart? Show your solution using G-R-
E-S-A method.

Given: mass 0.45kg Fnet - 90N

Required: a?
Equation: a = Fnet/m
Solution: a= 90N à 1kg/m/s² /0.45kg
Answer: a= 2 m/s²

Learning Task No.2 : Use the GRESA Method in solving the problem below.
Show your solutions. Write your answers in your notebook.

1. What is the mass of the cart with a constant net force of 200N is exerted
to accelerate from rest to a velocity of 40m/s in 10 s.
A. 0.5 kg C. 50 kg
B. 5 kg D. 500 kg

2. What is the acceleration of a ball with a mass of 0.40 kg is hit with a

force of 16N?
A . 0.4 m/s² C. 400 m/s²
B. 40 m/s² D. 4000 m/s²
3. What is the external net force exerted on a 3.5 kg papaya, which is being
pushed across a table and has an acceleration of 2.2 m/s² to the left?
A. 7.0N to the left C. 7.7N to the left
B. 7.5N to the right D. 7.7N to the right
4. What is the mass of a crate with a net force of 300N and accelerate it by
0.750 m/s²?
A. 0.4 kg C. 40 kg
B. 4 kg D. 400 kg

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The Law of Action and Reaction: Newton`s Third law of Motion

acts on it. Let a body A exerts a force on another body B, body B reacts against
this force and exerts a force on body A. The force exerted by body A on B is the
action force whereas the force exerted by body B on A is called the reaction force.

According to this law, the action is always accompanied by a reaction force

and the two forces must always be equal and opposite. Note that action and
reaction forces act on different bodies.

ØForces always occur in pairs (action and reaction forces).

ØAction and reaction are equal in magnitude.
ØAction and reaction are opposite in direction.
ØAction and reaction act on different bodies.
Here are some of the situations that deals practically in understanding the THrid
Law of Motion.
1. Pushing a car
Action force- the man pushes car
Reaction force- the car pushes man
When making a push to a car , a force is exerted
in a car, whose reaction will push us directly with the
same force in the opposite direction.

2.Hitting a ball
Action force- bat hits ball
Reaction force- ball hits ball

We exert an amount of force against the ball

with the bat, which in reaction exert the same
force on the wood. This is why the bat can break
while the balls are thrown
3.Deflating a balloon
Action force- air inside the balloon rushes
down
Reaction force the balloon moves upward
The air inside rushes down and the
balloon moves upward. In this situation, the
action is by the balloon that pushes the air out
of it when setting free. The reaction of the air
which escapes out from the balloon acts on the

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10
Week Balanced and Unbalanced Forces
2
Lesson
I
You learned that all objects fall because gravity pulls on them towards the
center of the earth. Examine the pictures below showing the pen and the flower
vase. But what makes the pen and the vase stays at rest? The pen stays in place
because of another force that acts on it that is supplied by the string which we
refer in physics as tension force (T). Tension force is the force which is
transmitted through a string, rope, or wire when it is pulled tight by forces acting
at each end. The vase on the other hand, stays at rest because of the upward
push exerted on it by the table which referred to as normal force. (Fn). Both the
tension force and normal force counteract the pull of gravity (Fg) that acts on the
objects, which makes them to stay at rest.

In both cases, you can now infer that the objects remained at rest because
the forces acting on the pen and on the vase are equal in magnitude and in oppo-
site direction and they lie along the same line of action. The forces are said to be
balanced.

What is balance force?

Balanced forces are forces that are equal in magnitude and in opposite di-
rection so there will be no motion in an object. Here are some examples where you
can see balanced forces. The arrow is the one that indicate the forces that act on
the rope and on the ground.

Combining Forces
For you to determine the net force or unbalanced force, you have to
recognize those forces that act along the same line of action. The algebraic sign +
and are used to indicate the direction of forces. Remember your lesson in
Mathematics, like and unlike sign. Unlike sign are used for forces acting in
opposite direction, like in the case of the ball lying on top of the table. The force of
gravity (Fg) and normal force (Fn) are assign opposite signs. Fn is given positive
sign (+) while Fg is given (-) sign. If both Fn and Fg are given a magnitude values
of 5 units , then the net force along the line will be.

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 You may follow the G-R-E-S-A method. What is this GRESA method? It is a
systematic way of solving a given problem.
G - given,
R required,
E equation,
S solution and
A Answer .

Let you go back again in activity 1. The vase on top of the table and on the
force diagram illustrated for the vase. The vase stays at rest because it has a
normal force of 5units and gravitational force of 5 units also. Lets find out will be
the net force of the vase?
(Photo taken from the LM.)
Given - Fn(Nornal force) = 5 units, Fg (Gravitational force) = 5 units
Required - F net ?
Equation - Fnet = Fn + Fg
Solution- Fnet = 5 units + (-5 units) = 0
Answer - = 0
If the sum of the force equate or equal to zero (0), the forces are considered
balanced. If the algebraic sum is not equal to zero, the forces are not balanced.
The non-zero sum is the net or unbalanced force. This unbalanced or net force

Unbalanced Forces
In a situation when a pen is attached to a sting, and then you cut the
string of the hanging pen, it fell down because there is no force acting on the
pen to counteract the pull of gravity.
If you push the vase on one side across, the vase will move but it will

of the applied force. So the forces acting on these objects are no longer
balanced.
If an object initially is at rest is under an unbalanced force, it moves in
the direction of the unbalanced force. How about if the object is in motion? How
will the unbalanced force affect its motion?

13 PIVOT 4A CALABARZON
Learning Task No. 1: Identify the situation if it shows balanced or unbalanced
force. Write your answer in your notebook.

. pulling a rope 2. standing still 3. tug of war 4. sky diving

However, there is another force that acts on the ball along the horizontal
line or along the force that makes the ball in motion. This is called friction force
(Ff). Friction is a force that acts between surfaces that are in contact with one
another. Friction in general acts opposite the direction of motion. In the case of
the rolling ball, the frictional force acts between the surface of the ball and the
table and slows down the motion of the ball. As the ball rolls to the right as
shown in the illustration friction acts to the left to delay its motion. Since no one
did push the ball continuously there is no force present to balance the force of
friction so the ball slowed down and eventually stopped.
Again because of the unbalanced force, the object changes its state of
motion, so you can say that it accelerates. Take note of this, acceleration is not
just an increase in velocity, but also a decrease in velocity.

Forces acting on a rolling ball

D
Learning Task No. 2: Study the diagram above. Answer the guide questions.

Guide Questions:
1. What do you call the force acting on the ball along the horizontal line or
along the force that makes the ball in motion?
2. What makes the ball stop on rolling after sometime?
3. What makes the ball keep on rolling?

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14
 Factors Affecting Potential and Kinetic Energy Week
3
Lesson
I

In this lesson, you learn the different factors that affect potential and ki-
netic energy. Energy is defined as the ability to do work. When work is being

English comes from the Greek word kinetikos (moving). Potential energy is pre-
sent when the work is waiting to be done, or when there is the potential for work
to be performed. It is affected by the mass of the objects and gravitational force.
The acceleration due to gravity is 9.9 m/s 2 or rounded off as 10 m/s2. The two
objects that are in the same position have potential energy, yet an object with
greater mass has greater potential energy, with respect to it position. An object of
the same mass that is placed at different position have different potential energy
contained. The object at a higher position will have a greater potential energy.
Kinetic energy is the energy of motion, potential energy comes from work having
been done on an object which was then stored.

Try to get a piece of rubber band. It has potential energy relative to its po-
sition when placed in your hands. It has the gravitational potential energy. If
you zinged the rubber band from your finger, then the potential energy has been
transformed into kinetic energy. While it was stretch waiting for you to release it,
it has potential energy again. It was stationary but work was done on it to move
it to its present position.

More work means more energy is provided to and stored by the rubber
band when it was stretched farther. When you release the rubber band, it has
more energy to move. More energy means more work can be done by the rubber
band. There is a connectedness between potential and kinetic energy. For moving
objects, you can calculate kinetic energy using the formula:
KE = (mass x velocity2)/2 or 1/2 mv2

Although mass and velocity both have great effects on kinetic energy, it is
velocity, more significantly, that determines kinetic energy. Observe the picture
below. Which picture of the child shows potential energy? Which of them
showed kinetic energy?

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 The kinetic energy of a particle is a single quantity, but the kinetic energy of
a system of particles can sometimes be divided into various types, depending on
the system and its motion. For example, if all the particles in a system have the
same velocity, the system is undergoing translational motion and has translation-
al kinetic energy. If an object is rotating, it could have rotational kinetic energy, or

system, relative to an internal frame of reference, may be called internal kinetic

energy. The kinetic energy associated with random molecular motion may be
called thermal energy. This various types of energy is associated that for every
kind of kinetic energy, it is the same physical quantity.

Learning Task No. 1: Analyze the picture below. Determine if it shows poten-
tial or kinetic energy. Write your answer in your notebook.

1. pushing the hammer into the nail 2. a boy walking in the street

3. the man holds the bow and arrow 4. the arrow approaching the dart board

5. the flower vase on top of the table

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 D
Learning Task No. 2: Compare Picture A and Picture B below. Answer the
guide question. Write your answer in your notebook.

Picture A Picture B

Image source: https://irp-cdn.multiscreensite.com/ d4114312/files/uploaded/

Guide Questions:
1. Which picture shows potential energy?
2. Which picture shows kinetic energy?
3. What factor (s) affect the potential energy?
4. What factor (s) affect kinetic energy?

Although mass and velocity both have great effects on kinetic energy, it is
velocity, more significantly, that determines kinetic energy. Study at the sam-
ple problem below.

What is the kinetic energy of a 45 kg object moving at 13 m/sec?

1. First we identify the information we are given in the problem:

mass = 45 kg velocity = 13 m/sec

2. Next, we place this information into the kinetic energy formula:

KE = 1/2 mv2 KE = 1/2 (45 kg)(13 m/sec)2

The kinetic energy value computed is 3802.5 J.

Note: The unit for energy is the same as for work: the Joule (J).

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 Effect of Temperature to the Speed of Sound Week
4
Lesson
I

This lesson to help you master propagation of sound. After going through each of
the learning tasks, you are expected to investigates the effect of temperature to speed of
sound.

Sound waves are examples of longitudinal waves. They also exhibit charac-
teristic features such as frequency, amplitude, wavelength, period and wave
speed. The alternate pushing and pulling mechanically exerts force on unit areas
of air particles and thus creating pressure waves. This alternating compressions
and rarefaction make up the longitudinal waves like sound waves.
The speed of sound may differ for different types of solids, liquids and gas-
es. For one, the elastic properties are different for different materials. Thus,
sound can travel faster in mediums with higher elastic properties than in lower
elastic properties. Another, the bond strength between particles also affects the
speed of sound. Thus, sound waves travel faster in solids than in liquids and fast-
er in liquids than in gases. While the density of a medium also affects the speed of
sound, the elastic properties have a greater influence on wave speed. Another
thing, the speed of sound is directly affected by the temperature of the medium.
Temperature is also a condition that affects the speed of sound. . Mole-
cules at higher temperatures have more energy, thus they can vibrate faster.
Since the molecules vibrate faster, sound waves can travel more quickly.
The speed of sound in room temperature air is 346 meters per second.
The speed of sound is the distance travelled per unit time by a sound
wave as it propagates through an elastic medium . The speed of sound in air is
about 343 metres per second (1,235 km/h at 20 °C (68 °F), ; 1,125 ft/s; 767 mph;
667 kn), or a kilometre in 2.9 s or a mile in 4.7 s. It depends strongly
on temperature as well as the medium through which a sound wave is propagat-
ing. Given normal atmospheric conditions, the temperature, and thus speed of
sound, varies with altitude. Examine the chart below. It is advised that during
storms or weather disturbances, the airplanes are given precautions in their
schedule of flight. Why do you think so?

Altitude Temperature m/s km/h mph mph

Sea level 15 O C (59OF) 340 1,225 761 661

11,000m-20,000m -57 OC (-70 OF) 295 1,062 660 573

(cruising altitude of
commercial jets and
first supersonic flight

29,000 m (Flight of X -48 OC (-53 OF) 301 1,083 673 585

-43A)

PIVOT 4A CALABARZON
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Learning Task No.1: Study the illustration below. Based on the lustration,
describe sound as a form of energy. Write your answer in your notebook.

https://www.physicsclassroom.com/class/sound)

Sound is________________________________________________________________________

Remember:
The speed of sound may differ for different types of solids, liquids
and gases.
Sound waves travel faster in solids than in liquids and faster in
liquids than in gases.
Sound can travel faster in mediums with higher elastic properties
than in lower elastic properties.
The speed of sound is directly affected by the temperature of the
medium.

Learning Task No. 2: Write TRUE if the statement is soundly correct and FALSE if the
statement is not correct. Write your answer in your notebook.
1. Sound is the energy things produce when they vibrate.
2. As the air moves, it carries energy in only one direction.

3. here are two different aspects to sound: the physical process and physiological pro-
cess.

Sound can travel through solids, liquids, and gases and even in a vacuum.

5. Sound waves are examples of longitudinal waves.

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 Hierarchy of Colors in Relation to the
Week
Energy of Visible Light
5
Lesson
I

This lesson will help you to understand concepts about light. After going
through this lesson, you are expected to explain the hierarchy of colors in relation
to energy of visible light.
Light is composed of colors of different frequencies and wavelength and the

ROYGBIV is the only part of the spectrum that can be seen by the naked eye. A
ray of white light that passes through a prism is dispersed into the visible spec-
trum. Red light is refracted the least, and purple light is refracted the most. his
is because the speed of the various wavelengths in glass is different, slowest for
violet light and fastest for red light. Red light has the lowest frequency and ener-
gy but the longest wavelength compare to other visible spectrum. Violet light has
the highest frequency and energy but the shortest wavelength compare to other
visible spectrum.
Using the diagram and the electromagnetic spectrum, you can see that vio-
let color has the shortest wavelength but highest frequency and the greatest
amount of energy while red color has the longest wavelength, lowest frequency
and least amount of energy. Can you tell the relationship between frequency and
wavelength of light ? Or the relationship between wavelength and the amount of
energy?

The electromagnetic spectrum is important to astronomers because celestial

objects emit waves in all the different regions of the spectrum. Visible light is very
small fraction of the visible spectrum.
At homes, light carries information in many ways. Cell phones use light to
send and receive calls and messages. Wireless routers use light to send pictures
of your family in Facebook from the internet to your computer. Car radios use
light to receive music from nearby radio stations. Even in nature, light carries
many kinds of information. Telescopes are light collectors, and everything we
know from Hubble is because of light. Since we are not able to travel to a star or
take samples from a faraway galaxy, we must depend

Hubble Space Telescope can view objects in more than just visible light,
including ultraviolet, visible and infrared light. These observations enable astron-
omers to determine certain physical characteristics of objects, such as their tem-
perature, composition and velocity

PIVOT 4A CALABARZON

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 Learning Task No. 1: Look at the given diagram of the glass prism below. This tells
about the dispersion of light. Using the diagram, answer the given questions below.

Figure 4: Glass Prism Dispersion of

light
(https:// i0.wp.com/passnownow.com/wp-
content/uploads/2014/07/glass-prism.jpg)

1. Based on the figure, what is the arrangement of colors from top to bottom?
2. Based on the concepts learned and by looking at the diagram, what are the
colors that have lower energy than the color blue?
3. What are the color/s that have higher energy than the color red?
4. What are the color/s that have higher frequency than the color red?
5. Which of the two colors: green or orange has the higher energy? Higher frequency?
Longer wavelength?

D
Learning Task No. 2: Examine the diagram showing the electromagnetic spec-
trum. Answer the guide questions based on your analysis of the diagram.

Guide Questions:
1. By looking on to the details giv-
en above in the diagram, what are the seven identified components of the
electromagnetic spectrum?

2.
that is found at the very middle?

3. By looking at the visible light, what specific color of light has the longest
wavelength? How about the shortest wavelength

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Week Heat vs. Temperature

6
Lesson
I

This lesson will give you understanding of the concepts about heat and temperature.
After going through this lesson you are expected to differentiate heat and temperature at
the molecular level. Look at the chart showing the difference between heat and tempera-
ture.

Heat Temperature

Is the quantity of energy absorbed or Is the measure of hotness and cold-

given off by an object ness of an object

Unit: Calorie Unit: Degree

Instrument measuring Instrument measuring

heat: Calorimeter temperature: Thermometer

In addition to these, we define heat as a transfer of (thermal) energy between ob-

jects or places due to temperature difference. Heat transfers from an object of
higher temperature to an object of lower temperature. Length, mass, and temper-
ature are measured quantities. So just like the meter for length and the gram for
mass, we need units for temperature. This can be provided by three different
scales, namely Fahrenheit, Celsius and Kelvin.
Heat is a form of energy and is measured in joules. It takes about 4.2
joules of heat to change 1 gram of water by 1 Celsius degree. A unit of heat still
common in the United States is the calorie.
Temperature is measured in degrees; heat is measured in joules. Tempera-
ture describes the average kinetic energy of molecules within a material or system
and is measured in Celsius (°C), Kelvin (K), Fahrenheit (°F), or Rankine (R). It is a
measurable physical property of an object also known as a state vaiable. Other
measurable physical properties include velocity, mass, and density. THe diagram
shows the difference between ehat and temperature at molecular level.

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 In general, the Second Law of Thermodynamics states that heat will always flow
spontaneously from hotter substances to colder ones. This simple statement ex-
plains why an ice cube doesn't form outside on a hot day or why it melts when
dropped in a bowl of warm water.
In a thought experiment, an ice cube dropped into a bowl of warm water
gained heat (thermal energy) from the water in the bowl . Adding thermal energy
leads to an increase in the kinetic energy of the ice molecule, and thus an in-
crease in temperature. This is known because temperature is in fact the measure
of the average kinetic energy of the molecules. Furthermore, the ice will continue
to gain thermal energy causing its molecules to move faster and eventually break
their intermolecular bonds or melt.
In conclusion, the transfer of heat or thermal energy will typically change
the temperature of the substance, but not always! For example, at the moment
when the ice in the bowl turns to water those water molecules will be at the exact
same temperature as when they were ice. In this case, instead of the thermal en-
ergy doing work to increase the kinetic energy, it does work to break the intermo-
lecular bonds, causing a change of state. However, as time goes on the tempera-
ture of the recently melted ice will increase until everything within the bowl reach-
es equilibrium meaning a consistent temperature throughout.

Learning Task No. 1: Look at the illustration, what concepts of heat are being
shown in this picture?
_______________________________________________________________________________
_______________________________________________________

Heat and Temperature

- - - -

Learning Task No. 2: Using the same diagram above, state the Second Law of
Thermodynamics. Write three sentences on the differences between heat and
temperature.

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29
 Relationship Between Current and Voltage Week
7
Lesson
I

This lesson will help you master concepts about electricity. After going through
the lessons and learning tasks, you are expected to infer the relationship between current
and charge. Every bit of matter, wires included, contains enormous numbers of electrons
that swarm about in random directions. When they are set in motion in one direction, a
net direction, we have an electric current. The rate of electrical flow is measured in am-
peres.
When water flows in a pipe, there is more pressure on one end than the other.
There must be a pressure difference to keep the water flowing. Similarly for electric cur-
rent. Electrons flow in a wire only when a difference in electrical pressure exists.
The name for electrical pressure is voltage. How much current there is depends
on the voltage, and also on the electrical resistance of the circuit. Electrical resistance is
measured in units called ohms.When they are set in motion in one direction, a
net direction, we have an electric current.
The rate of electrical flow is measured in amperes (abbreviation A).
Electrons flow in a wire only when a difference in electrical pressure exists.
The name for electrical pressure is voltage. How much current there is
depends on the voltage, and also on the electrical resistance of the cir-
cuit. The relationship between voltage, current, and resistance is Ohm dis-
covered that the amount of current in a circuit is directly proportional to the voltage
across the circuit and inversely proportional to the resistance of the circuit:

Current = Voltage .
Resistance
Or, in units form:

Ampere = Volts .
Ohms

as I = V/R. It can also be written, V = IR, or R = V/I, so if any two variables are known,

The formula to get the amount of voltage, current and resisitance is given in the diagram
below.

PIVOT 4A CALABARZON
31
Learning Task No. 1. Using the concepts you have learned, complete the table
with appropriate answers based on the relationship of voltage, current and re-
sistance.

Quantity of Symbol Definition Unit of Unit abbre- Instrument

Electricity Measure- viation to measure
ment
Voltage
Current
Resistance

D
Learning Task No. 2: Read and understand the sample problem using GRESA Method.
Solve the problem . Show the solutions in your notebook and encircle the final answer.

1.Use GRESA Method to solve for

How much current flows through a the amount of current that will
lamp with a resistance of 60 ohms when flow in a lamp with a resistance
the voltage across the lamp is 12-V?
of 40 ohms when the voltage
G: R = 60 ohms across the lamp is 15 V.
V = 12 volts

R: I = ? 2. Find the voltage if the re-

E: I = V sistance is 30 ohms and the cur-
rent is 0.5 amperes.
R

S: I = 12 volts

60 ohms 3. Find the resistance if the cur-

rent is 1.5 amperes and the volt-
age is 15-V.

E
Learning Task No. 3: Use the diagram showing the relationship among current, re-
sistance and voltage. Explain the relationship between current and voltage; voltage and
resistance; current and resistance. Write your answer in your notebook.

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32
 Advantages and Disadvantages of Series and Parallel
Week Connection
8
Lesson
I

In this lesson, you will learn the importance of series and parallel circuit
connection. The lessons and learning tasks will help you to explain the ad-
vantages and disadvantages of series and parallel connections in homes.

Examine the diagram of a series and parallel connection below.

How did the two circuits differ?

A series circuit is a circuit in which resistors or loads are connected end to

end so that the circuit will have only one path through which electric current
flows. Thus, when a number of resistors are connected in series, the effective re-
sistance (total resistance in the circuit) is gotten by adding the individual re-
sistance algebraically.

In series connections, the same current flows across all the branches of the
circuits, but different voltage across it thus making the resistors to have different
voltage across them. Each resistor or load will experience a voltage drop. The ap-
plied voltage is equal to the sum of the voltage drop across the different parts of
the circuit. Voltage drop is proportional to the resistance current being the same
throughout the circuit. When loads are connected in series, the loads will tend to
have a common switch. This kind of connection is employed in school halls, street
lights. The problem with this kind of connection is that when a load develops a

connection. Till a load gets energy before it delivers it to the other and the one to
deliver fails, there will be a black out.

Resistors, loads are said to be connected in parallel when the end of each
of the resistors or loads have a common point or junction and the other ends are
also connected to a common point or junction. Such circuits are known as paral-
lel circuits. Unlike the series circuit connection, when finding the total (effective)
resistance in a parallel circuit, the reciprocal of the individual resistance is taken.
Thus, when a number of resistances are connected in parallel, the reciprocal of
the effective resistance is given by the arithmetic or algebraic sum of the recipro-
cal of the individual resistance.

Parallel circuit connection is very common in use. Various lamps and elec-
trical appliances in our homes are connected in parallel so that each of the lamps
or bobs and appliances can be operated independently. For us to have control
over the individual lamps or loads, they have to be wired in parallel.

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Learning Task No. 1: Give examples of appliances at home that are installed
using series connection. Draw the circuit in a series connection in your note-
book.

D
Learning Task No. 2: Give an example of appliances at home that are installed
using a parallel connection. Draw the circuit in a parallel connection in your
notebook.

E
Learning Task No. 3: Make a chart that will explain the difference between
parallel and series connection in a circuit in terms of current. Voltage, re-
sistance, pathway of flow of electric current, brightness of bulbs, if breaks occur
in circuits, battery status, and applications.

Criteria Series Connection Parallel Connection

Current
Voltage
resistance
Pathway of flow of electric cur-
rent
Brightness of bulbs
If breaks occur in a circuit
Battery status
applications

A
Learning Task No. 4: Make a list of the advantages and disadvantage of series
and parallel connections at home. Complete the chart below.

Series Connection Parallel Connection

Advantages

Disadvantages

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 Safety Devices at Home

Lesson
I
Congratulations! You are now in the last lesson in this module. This les-
son will help you to explain the functions of circuit breakers, fuses, earthing,
double insulation, and other safety devices in the home.
Electricity has two hazards. A thermal hazard occurs when there is elec-
trical overheating. A shock hazard occurs when electric current passes
through a person. There are safety devices that will prevent these hazards.
Read the concepts about these safety devices.

Circuit breakers: It functions to break the circuit when the current in the cir-
cuit exceeds the maximum value, and is no longer considered safe. To do this
there is an electromagnet that will physically break the circuit when it detects
that the current has exceeded its maximum.

Fuses: Fuses are like circuit breakers in that they will break a circuit when it
detects that it is too dangerous to operate. Fuses use a resistance wire with a
low melting point instead of an electromagnet, and when the current is too great
the wire melts and the circuit will is broken. As the fuse melts every time the
current is too great, it must be replaced, unlike the circuit breaker, which can
be reset after it breaks the circuit.

Earthing: There are three wires that supply power to households. These are the
active, neutral and earth wires. Earth wires are put in so that electric shocks can
be avoided when people come into contact with an active wire that is in contact
with the casing of any connected appliances. If there was no earth wire a person
would complete the circuit between the appliances and the ground, and would
receive an electric shock. To reduce the chance of this happening, the earth wire
provides a better conductive path for the current. If the current comes into con-
tact with the casing of an appliance, the earth wire will create a conductive path
from the appliance to the earth, and a large current will flow to the earth through
this connection. This large current will also blow any fuses or trip any circuit
breakers, so that the circuit is not complete, and any person touching the appli-
ance will not receive an electric shock.

Double insulation: Insulation is installed so that wiring and electric appliances

are covered so that the current will only go through its intended path. The insula-
tion is made out of an extremely poor conductor in order to create a safe path for
the current to flow through. To increase the safety from insulation, a second layer
of insulation can be installed, so that if one of the layers fails to properly insulate
the circuit, the second layer will still be able to protect it.

Residual current devices: RCDs are designed so that they can stop a current
before it becomes harmful to a person. It does this by detecting any leakages
from the circuit through a differential current transformer, that will compare the
current flowing through the live and neutral conductor, and if there is a differ
ence it quickly shuts down the current. It typically shuts it down in 25-40 mill
seconds after a leakage conductor, to minimize the damage done to the body.

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