Electricity

Key words:
1 Electric The rate of flow of electric charges, the charges carry
current electrical energy from one place to another through a circuit
(closed loop).
2 Ampere (A) The SI unit of current, also known as amp.

3 Voltage The force from an electrical circuit's power source (such

as battery) that pushes electrons through a conducting
loop,allowing them to do work.
4 Volt(V) It is the unit of Voltage.

5 Resistance Resistance measures how well a material conducts

electricity. Low resistance means the object conducts
electricity well, high resistance means the object does not
conduct electricity well.

6 Ohm (Ω) It is the unit of resistance.

 What we will Learn…
• What is a current?
• How to draw electric circuit diagrams
• What is potential difference, voltage?
• What is resistance?
• S/E: Circuits arranged in series versus parallel
• S/E: Fixed resistors versus variable resistors
• Effects of electric current
 Key words:
7 Circuit Simplified conventional graphical representation of an electrical
diagram circuit.
8 Series circuit A series circuit consists of a single pathway through which
electricity can flow. All of the parts—power source, wires, and
devices—are connected along the same pathway; the devices
are connected one after another, with no branches.
9 Parallel In a parallel circuit the current is divided into separate paths,
circuit branches where all parts are connected across each other

10 Ammeter An instrument for measuring electric current in amperes, always

connected in series.

11 Voltmeter An instrument for measuring voltage in volts, always connected

in parallel.
12 Variabl A device that allows the resistance to be changed by turning a
e shaft or sliding a control, helps to control the current in a
resistor circuit.

13 Buzzer An electric signaling device that makes a buzzing sound.

 What is Electricity???

Definition:

Electricity is a form of energy that can

be easily changed to other forms.
Where does Electricity come from?
Mainly 2 sources:
1) Power Stations
- Supply a lot of electricity
-Used in many electrical
appliances
2) Electric Cells (batteries)
- Supply a little electricity
- Portable
- Safe
 How does an Electrical
Appliance Work?
• To make an electrical appliance work,
electricity must flow through it.
• The flow of electricity is called an electric
current.
• The path along which the electric current
moves is called the electric circuit.
What is an Electric Current???
electric
cell connecting
wire
filament

flow of electrons

Definition:

An electric current is the rate of flow of electric

charges in a circuit.
 Electric Charges
• Electric charges are made up of positive
charges (protons) and negative charges
(electrons).

• When these charges flow in a circuit, a

current is produced.
 How does electricity flow?
• The battery in a circuit gives energy to
the electrons and pushes them around
a circuit, from the negative terminal of
the cell, round the circuit and back to
the positive terminal of the cell.
 How to Measure Current?
• The SI unit for electric current is ampere (A).
• Smaller currents are measured in
milliamperes (mA).

1 A = 1,000 mA

1 mA = 0.001 A

• Different electrical components and

appliances require different sizes of current
to turn them on.
 Instrument to Measure Current
• An ammeter is an instrument used for
measuring electric current.
 Ammeter
• It must be connected in series in the circuit.

• Positive side of ammeter must be connected

nearest to the positive terminal of the battery
(electric cell), and vice versa.
 Electric Circuits
• Electric circuits are
connecting wires
made up of electrical
components electric cell

• These components
must be joined
together without any
gap in between to
light bulb circuit board
form a closed circuit.
Note:
Components refer to the
light bulb, wires, battery
 Electric Circuits
• Incomplete circuits are called open circuits.

connecting wire is no source of

missing electrical energy

Both the circuits in the diagram are incomplete, hence they are known
as “open circuits”.
 An electric current flows
only when there is:
• a source of electrical energy and

• a closed circuit
connecting wires

electric cell

light bulb circuit board

 How to draw Circuit Diagrams
Component Symbol Component Symbol

+ +

An electric cell Battery

Switch (open)

Light bulb (lamp) Switch Switch (closed)

Connecting wires Connecting wires

(not joined) (joined)

Symbols are used to represent the various electrical

components in circuits.
 Switches
A switch is used to open or close a circuit.

Main switch used

in buildings

Switches used on circuit

Circuit diagrams for open
and closed circuits

Open circuit. Close circuit.

Bulb does not Bulb will light
light up when up when the
the switch is switch is
Series and P a r a l l e l
There are 2 ways in which an
electric circuit can be
arranged:

1. Series
2.Parallel
 Series Circuit
• A series circuit connects the components one
after the other
• A single loop is formed
• A break in any part of a series circuit stops the
flow of current in the whole circuit.
 P a r a l l e l Circuit
• A parallel circuit divides into two or more branches.
• The current divides and flows through each parallel
branch.
• If a component breaks or is removed, the other
components remain on.
 Which of the following is a
series circuit?
Which is a parallel circuit?

Series Circuit P a r a l l e l Circuit

Draw the circuit diagram f o r
the f o l l o w i n g set up and state
whether it is a series o r
p a r a l l e l circuit.
Draw the circuit diagram f o r
the f o l l o w i n g set up and state
whether it is a series o r
p a r a l l e l circuit.
Which is brighter?
 Which of the following is a
series circuit?
Which is a parallel circuit?

Series Circuit P a r a l l e l Circuit

 Voltage
• An electric cell gives energy to the electrons and
pushes them round a circuit. Voltage is a measure
of how much energy the electrons receive.

• Different voltages are supplied by different cells and

batteries.

1.5VDry Cell

12VCar Battery 9 VDry Cell

 How to Measure
Voltage?
• The SIunit for voltage is volt
(V).
• Avoltmeter is an instrument
used for measuringvoltages.
 Voltmeter
• Voltmeters must be connected
in parallel to thecircuit.
• The positive side of voltmeter
is connected to the positive
terminal of the cell, and vice
versa.
 Recall: Ammeter!!!
• It must be connected in series in the
circuit.
• Positive side of ammeter mustbe
connected nearest to the positive
terminal of the battery cell and
vice versa.
Potential Difference
(P.d.)
 Resistance
• When an electric current f l o w s
through a circuit, there w i l l be
some resistance that opposes it.
(similar to friction)
 Resistance
• Good conductors o f electricity
have LOW RESISTANCE. (Eg. Met al
objects)
–Electricity is able t o f l o w
through them very easily
• Po or conductors o f electricity
have HIGH RESISTANCE. (Eg. Wood,
cloth)
–Electricity is not able t o
 Resistance
• The SI unit f o r resistance is ohm ()
• Different e le ctr ic al components
have different resistance
• For example, nichrome wires have a
higher resistance than copper wires.

So should we use
nichrome o r copper
t o make wires?
 Resistors
• An electrical component that is specially made to have a
certain resistance is called a resistor.
• They can be connected in a circuit to resist the current
flow.

P a r a l l e l Circ
 Example 1
• An electri c rice cooker
operates at 240 V and uses a
current o f 8 A. What is the
resistance o f the rice cooker?
240
Voltage R=
8
(V) =240 V
= 30 
Current (I) V
=8 A R =
I
 Fixed Resistors and
Variable Resistors
• Fixed resistors have only one resistance value
• Variable resistors can be adjusted to change
the resistance.

fixed resistor symbol variable resistor symbol

•Variable
resistors are
useful in light
dimmers and
 What we will Learn…
• What is a current?
• How to draw electric circuit
diagrams
• What is potential difference,voltage
and E.M.F?
• What is resistance?
• S/E: Circuits arranged inseries versus
parallel