Grade 12 IEB Physical Science - Electric Circuits Summary
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Course
Physical Sciences
Institution
12th Grade
This Grade 12 IEB Physical Science guide covers the fundamentals of electric circuits, including Ohm’s law, resistance, and circuit elements (series and parallel configurations). It explains concepts like internal resistance, emf, potential difference, and energy calculations, with practical exam...
FIFATDIS SIDDIIIIIITC) &
ohmic conductor Energy and Power
nin nin straight line graph
electrical
that passes through origin energy
>
=
h
- (directly proportional N Pt W VIt W PRE W
T =
=
or or =
or
(meausered in
joules (J)]
E gradient of graph () represents the resistence (R)
E mf (3) and potential difference (v) note : a device called a fuse is used for safety in appliances. It
<
emf : the total energy supplied per coulomb of charge by the battery (in Volts)
> of the conductor
the resistence of conductor does not
melts When current is too high ,
so that the circuit will open.
vary with >
electrical power
↳
measured across terminal of battery when no flowing through battery
&
charge is 8
current (A) current. (current must be low-higher current ↳ the rate at which electrical
energy is dissipated in a resister
potential difference : the amount of work done (w) per coulomb of charge independant
Y E
-
can cause metal to heat up increasing resistence P = or P =
VI or P = or P =
PR
↳ terminal pd :
measured across terminals of a battery when charge is
flowing < this is when the conductor becomes non-ohmic as resistence now varies (measured in Watts (N))-C 5 .
domestic appliances are marked power
. Work done(
-
ratings which indicates
with current
iv- the power delivered to an appliance when connected to 240V supply
measured in volts (v)
increasing resistence (non-ohmic) electricity usage
of
"
F
temp increase
- :li parallel
-
series :
kWh
:
↳ electrical energy consumed is measure in
greater emf is obtained
· emf of battery is same a single cell constant cost =
power rating (kW) x time used (n) X price per kWh
·
resistence (ohmic)
fixed temp
(straight line)
-
1e I cell 51
Resistenceord
15 1
12 I cell is 1 5V
Internal
.
,
,
.
o
current (A)
4 5 battery emf 1 5V
battery emf .
is .
internal resistence of a
battery is treated as another resister
&
esistors
In series with the external resistence. : emf = Vext + Vost
> voltmeter :
measures potential difference across a circuit component (voltage)
Inserted into circuit to control the current
>
(high resistence =
small current < emf (3) : the terminal pd when circuit is open and zero current is
-connected in parallel , as it has a very high resistence - v
In the external circuit
and low resistence= high current)
Current (1) · pen switch closed switch
> for constant voltage , the current in a resistor is inversely
current in external circuit Is current
at battery 3
in external circuit
-current :
the rate of flow of charge (a) proportional to the resistence I current
zero
vemofbateryermvagembatanal
charge (c)
. terminal term
>
F times
-
I um I
I I
IA =
10 S
resistor variable resistor light bull
.
the
voltage across internal resistence will
III Internal
external circuit (lost
amperes (A)]
not be used in
(measured in
resistence volts) Viost Ir
factors that affect the resistence in a conductor
=
>
emf =
Vext + Vost
↳ conventional current positive charge moves from the positive terminal formula
(longer-greater resistence
:
1) ) length of conductor emf = I (Rext + r)
to negative terminal of battery 2 )
. thickness of conductor (thicker =
lower resistence) Increasing external resistence
&
)
↳
electron flow electrons more from the to the terminal
:
negative positive 3 ) type of material (different metals have different resistences) ↳
Will result in a decrease in circuit current· thus internal
pd across
.
Ammeter measures current in a circuit component A
(greater (Vost Ir)
< :
4) temperature of conductor temperature= greater resistence resistence will also decrease =
this will cause an increase
,
-
connected in series have very little resistence (don't affect current)
In the terminal potential difference (Vext =
emf-Vlost)
and parallel networks of resistors
,
series
Resistence and Ohm's Law reasing
series parallel &
extern
resistence
the flow of charge divided (split)
resistence (R) : A material's opposition to current increase in circuit current thus pd Internal
is
>
current (1) current is the same in each ↳ Will result in an . across
resistor amongst the resistors
< ohm's law Current :
through a conductor is directly proportional difference resistence will also increase (Viost =
Ir) ,
this will cause a decrease
conductor Voltage divided (split) the same across
across the at constant temperature . potential
is
Voltage is
in terminal potential difference (Vext =
emf-Vlost)
difference (v) amongst the resistors each branch
>
-
current (A) A short circuit : A path of very low resistence (Rext almost zerp)
Voltage (v)
Y ~
resistence (2-ohm's
resistence (R) R += Ri +
Ra + Rs ...+ and maximum current is created .
current in the wire]
[Wires and battery get very not due to
the high
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