analysing electric fields and
Physics form 5 chapter 2
• A student is able to :
• •State the relationship between electron
flow and electric current.
• •Define electric current
• •Describe and electric field
• •Sketch electric field lines showing the
direction of the fields
• •Describe the effect of and electric field
on a charge
• •Solve problems involving electric charge
• Think how electrical energy makes
the electrical equipment function.
• This chapter will assist you in your
understanding of the concept of
• An atom is a fundamental unit of
matter made up of
• protons (with a positive charge)
• neutrons (neutral – no charge)
• electrons (with a negative charge)
What is electricity?
• Everything is made of atoms which contain
POSITIVE particles called PROTONS and
NEGATIVE particles called ELECTRONS.
• An atom will usually have the same number
of positives and negatives
• This makes the atom NEUTRAL.
• In some materials, particularly
metals, the electrons farthest from
the nucleus are not bound to a
particular atom - they can move
freely from one atom to another.
• Electricity is the flow of these free
electrons in a wire
• Electric charge is given the symbol
• Electrons are the charge
• that flow in an electrical circuit –
• from the negative to positive
• Electric current consists of a flow of
• The more charges that flow through a
cross section within a given time, the
larger the current
charge• Good conductors allow
electrons to move
• through them easily.
Insulators do not allow
electrons to move
What makes these free
• Suppose we put something that has a net
positive charge at the one end of the wire
(say, at the right end of the wire pictured
above). Let's also suppose that we put
something with a net negative charge at
the other end (the left end in the wire
above). Then the electrons in the wire will
be attracted to the positive end and
repelled by the negative end. Hence, they
will flow from left to right. That's
• Charge is measured in
• which is given the symbol
• The charge on a proton is
•1.6 x 10-19C
• which is the same size as the charge on an
Amount or Sum of Charge
Sum of charge
= number of charge particles charge of 1
= n x e
So, what is electricity?
Electrons have a negative charge
(Q) measured in coulombs (C).
Electrons move round a circuit from
negative to positive (remember like
charges repel, opposites attract)
giving rise to an electric current.
What is electricity?
So electricity is…
movement of electrons or flow of
charge round a circuit.
We call this electric current.
Charge, Current & Time
• Electric current is given the symbol
• Electric current is a flow of
• negative charges (electrons) in a
Charge, Current & Time
• Current is rate of flow of charges
OR the amount of charge flowing
per second and is given the unit
• Unit for current is Ampere (A)
• I = Q/t,
• where I = current
• Q= Quantity of charges (Coulombs)
• t= time (second)
• 1 Ampere is 1 coulomb, C in one
Measuring Current -
• To use the ammeter in the
measurement of an electric
current, the ammeter must be
connected in series to the circuit.
1. An electric field exists in the space surrounding a
• 2. Like charges ___________ each other ,
unlike charges __________each other.
3. An electric current is defined as
5. Electric current, , (Q measured in
6. ___________, C)
• 4.Electric current is measured with an
______________ in SI unit _____________
the rate of flow of electric charge
ammeter Ampere, A
• A battery is connected to a bulb
and a current of 2mA flows through
it. What is the time taken for the
battery to deliver 2 C of charge?
A. 1 s
B. 10 s
• An electric oven has been switched
on for 2 hours. Calculate the
quantity of electric charges passing
through the circuit in this time if
the current is 0.5A
• The electric current supplied by a
battery in a digital clock is 0.5mA.
a) What is the quantity of charges
that flow in half an hour?
b) Find the number of charges that
flow through the clock?
[e=1.6 x 10-19C]
a) Q = It
= 0.5 x 10-3 x 0.5 x 60 x 60
= 0.9 C
b) Q = ne, where n is the number of
electrons and e is the charge of 1
Therefore the number of electrons,
n=Q/e = 0.9/1.6 x 10-19 = 5.625 x 10-18
• Electric Field is the region where
an electric force is experienced
Lines of force:
Lines of Force are used to represent
the direction of an electric field.
A positive charge A negative charge
As we move closer
to the charge,
the electric field
The electric field lines neither branch
off nor intersect one another.
• Electric field patterns.mp4
Electric Field Pattern
The fields for four
1. Two unlike charges –
2. Two like charges –
3. A charge and an
4. Two oppositely
(The direction of the
arrows shows the way a
positive charge would
move if placed in the
Two similar charges repel each other
Two opposite charge attract each other
Effect of Electric Field Acting
On A Charged Body
Candle in the electric
• Heat energy from the
candle flame produces
ionization of air molecules
to form positive and
• Movement of positive ions
which are heavier towards
the negative plate causes a
bigger spread of the flame.
• Negative ions which are
lighter move towards the
positive plate and causing a
smaller spread of the
• Van De graaf
Van De Graaf generator
• Schematic view of a
classical Van de Graaff-
1) hollow metal sphere
2) upper electrode
3) upper roller (for example
an acrylic glass)
4) side of the belt with
5) opposite side of the belt
with negative charges
6) lower roller (metal)
7) lower electrode (ground)
8) spherical device with
negative charges, used to
discharge the main sphere
9) spark produced by the
difference of potentials
1. Made up of the flow of tiny electric
charges called electron
2. Static electricity is a build up of these
tiny electric charges in one place until
the electrical charge is discharged.
3. 3. As an example the ruler rubbed with a
clothes, it is charged but static
electricity because insulator does not
allow flow of the charges. If we use a
metal object or a conductor,
Electric Field Lines
1. Always extend from positively
charged object to negatively
2. Positively charged object to
3. Infinity to negatively charged
4. Never cross each other
5. More dense around the objects with
the greatest amount of charge.
• Thanks to those whose untiring efforts in
creating images that made other’s life easier.
• The images and contents of the slides are
extracts and adapted from various sources/
• Send me an email if you discover any error in the
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