This document discusses key concepts in electric circuits, including Ohm's Law, series and parallel circuits, and internal resistance. Ohm's Law describes the relationship between current, potential difference, and resistance for circuit elements. The equivalent resistance of resistors can be calculated differently depending on whether they are connected in series or parallel. Real batteries have an internal resistance that affects their potential difference output.

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10. Electric circuits
Physics
Grade 12

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Revision
Ohm’s Law governs the relationship between current and potential difference for a circuit
element at constant temperature. Mathematically we write:
Conductors that obey Ohm’s Law are called ohmic conductors; those that do not are called non-
ohmic conductors.
Ohm’s Law can be applied to a single circuit element or the circuit as a whole (if the components
are ohmic).
I=
V
R

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Series and parallel circuits
The equivalent resistance of resistors in series (Rs
) can be calculated as follows:
The potential difference and current for series
circuits is given by:
The equivalent resistance of resistors in parallel (Rp
) can be calculated as follows:
The potential difference and current for parallel
circuits is given by:
Rs=R1+R2+R3+ … +Rn
VT=V 1+V2+V 3+ … +V n
IT=I1=I2=I3= … =In
1
Rp
=
1
R1
+
1
R2
+
1
R3
+ … +
1
Rn
IT=I1+I2+I3+ … +In
VT=V 1=V2=V3= … =V n

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Internal resistance
Real batteries have an internal resistance.
The potential difference V of the battery is related to its emf Ɛ and internal resistance r by:
The external resistance (R) in the circuit is referred to as the load.
ℇ=V +Ir

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