PRIVATE TUTORING
(NOTES)
MR SB.
MOKOENA
076 377 6747
075 263 2773
mokoenaselby2@gmail.com
GRADE 10 – 12 ELECTRIC CIRCUITS
SYMBOLS
POTENTIAL
Symbolised by V, measured by
Measure of energy, per unit of
DIFFERENCE
a Voltmeter using the units of
charge, transferred between
Volts (V)
two points in a circuit.
Symbolised by I, measured by a
The rate at which charged
Ammeter using the units of
particles, like electrons, flow
Amperes (A)
through an electrical circuit.
ELECTROMOTIVE
Symbolised by (Emf) measured
Electromotive force is an
FORCE (E)
in Volts. The maximum energy
energy transfer to an electric
per charge.
circuit per unit of electric
ELECTRIC CURRENT
charge, measured in volts.
OTHER EXPLANATIONS
• Potential difference – the work done in moving a charge from a point of low potential
to a point of high potential in an electric field.
• Electric current – the number of charge passing a point in a second.
• Resistance – the ability of a conductor to impede the movement of charge given by
the ratio of the potential difference across a conductor and the current passing through
it. Resistance is measured in ohms (Ω)
• Ohm’s Law – the current through a conductor between two points is directly
proportional to the potential difference across the two points, and, inversely,
proportional to the resistance of the conductor, provided the temperature remains
constant.
• Internal resistance – the extent to which an energy source, like a battery, impedes the
flow of charge within itself.
The potential difference in a circuit is denoted by the letter V. It is defined as the
energy needed to move a charge from one point to another in an electric field. It is
measured in volts (V). Electric current is the movement of charge. The letter, I , is used
as a symbol for electric current. It is defined as the number of charge passing appoint in
a unit time.
OHM’S LAW
The electric current through a conductor
between two points is directly
𝑹=
𝑽
𝑰
proportional to the voltage/potential
difference & inversely proportional to
resistance across the two points.
SERIES CIRCUIT
PARALLEL CIRCUIT
RESISTORS IN SERIES
RESISTORS IN SERIES
𝑹𝑻 = 𝑹𝟏 + 𝑹𝟐 + 𝑹𝟑
(total effective resistance, add all the
resistors)
CURRENT IN SERIES
𝑰𝑻 = 𝑰𝟏 = 𝑰𝟐 = 𝑰𝟑
(The current across is the same)
𝟏
𝟏
𝟏 −𝟏
+
+ ]
𝑹𝟏 𝑹𝟐 𝑹𝟑
(total effective resistance, add all the
𝑹𝑻 = [
resistors in fraction inverse form)
CURRENT IN SERIES
𝑰𝑻 = 𝑰𝟏 + 𝑰𝟐 + 𝑰𝟑
(The current is divided or shared
POTENTAL DIFFERENCE
𝑽𝑻 = 𝑽𝟏 + 𝑽𝟐 + 𝑽𝟑
(Potential Difference is shared across
each resistor from the total)
NB: Series is also called
“Potential/Voltage Divider”
across is the resistors in equivalence to
the ratio)
POTENTAL DIFFERENCE
𝑽𝑻 = 𝑽𝟏 = 𝑽𝟐 = 𝑽𝟑
(Potential Difference is the same
across all resistors)
NB: Parallel is also called
“Potential/Voltage Divider”
FORMULAS
𝑒𝑚𝑓 = 𝐼(𝑅 + 𝑟)
𝑃 = 𝑉𝐼
𝑃 = 𝐼2 𝑅
𝑃=
𝑉2
𝐼 = 𝑡𝑜𝑡𝑎𝑙 𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐 𝑐𝑢𝑟𝑟𝑒𝑛𝑡
𝑅 = 𝑡𝑜𝑡𝑎𝑙 𝑒𝑥𝑡𝑒𝑟𝑛𝑎𝑙 𝑟𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒
𝑟 = 𝑖𝑛𝑡𝑒𝑟𝑛𝑎𝑙 𝑟𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒
NB: If they did not provide
𝑃 = 𝑝𝑜𝑤𝑒𝑟
𝐼 = 𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐 𝑐𝑢𝑟𝑟𝑒𝑛𝑡
𝑉 = 𝑝𝑜𝑡𝑒𝑛𝑡𝑖𝑎𝑙 𝑑𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒
𝑅 = 𝑟𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒
Power is the amount of energy
𝑞 = 𝐶ℎ𝑎𝑟𝑔𝑒
𝐼 = 𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐 𝑐𝑢𝑟𝑟𝑒𝑛𝑡
∆𝑡 = 𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑡𝑖𝑚𝑒
Electric charge (symbol q,
𝑅
𝑞 = 𝐼∆𝑡
internal resistance, or they say it
is negligible - Use zero (0).
transferred or converted per unit
time.
sometimes Q) is a physical
property of matter that causes it
to experience a force when placed
in an electromagnetic field.
𝑊 = 𝐼2 𝑅∆𝑡
𝑊 = 𝑤𝑜𝑟𝑘 𝑑𝑜𝑛𝑒
𝐼 = 𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐 𝑐𝑢𝑟𝑟𝑒𝑛𝑡
𝑅 = 𝑟𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒
∆𝑡 = 𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑡𝑖𝑚𝑒
Work- refers to the energy
transferred when a charge moves
through an electric field
Practice
1. A battery with an emf of 20 V and an internal resistance of 1Ω is connected
to three resistors as shown below.
Calculate:
a) The current in the 8Ω resistor ……………………………………………………….. (6)
b) Potential difference across the 5Ω resistor ……………………………………. (4)
c) Total power supplied by the battery ………………………………………………. (3)
2. Study the circuit below and answer the questions
With Switch S closed the current passing through the 8Ω is 0,5A
a) State Ohm’s law in Words …………………………………………………………………………….. (2)
b) Calculate the reading on Ammeter 𝑨𝟏 ………………………………………………….......... (4)
c) If device R delivers power of 12 w, calculate reading on Ammeter 𝑨𝟐 ........ (5)
d) Calculate the reading on the voltmeter when switch S is closed. …………….... (3)
MOKOENA SB
076 377 6747 / 065 263 2773
mokoenaselby2@gmail.com