This document discusses key concepts in electric circuits including potential difference, electromotive force (emf), current, resistance, and how these concepts relate to different circuit configurations. It defines potential difference and emf as the voltage across battery terminals when not or in a complete circuit. Current is defined as the rate of charge flow measured in amperes. Resistance depends on the material and physical characteristics of a circuit element and is measured in ohms. Resistors in series have the same current but their voltages add up, while resistors in parallel have the same voltage but their currents add up. Measuring devices like voltmeters and ammeters must be connected appropriately.

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17. Electric circuits
Physics: Electricity and magnetism
Grade 10

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Potential difference and emf
The potential difference across the terminals of a battery when it is not in a complete circuit
is the electromotive force (emf) measured in volts (V).
The potential difference across the terminals of a battery when it is in a complete circuit is
the terminal potential difference measured in volts (V).
Voltage is a measure of the work required/done to move a certain amount of charge and is
equivalent to J·C−1
.

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Current
Current is the rate at which charge moves/flows and is measured in amperes (A) which is
equivalent to C·s−1
.
Conventional current flows from the positive terminal of a battery, through a circuit, to the
negative terminal.
We use the symbol I to represent current. We can calculate current using:
I=
Q
Δt

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Measuring current and potential difference
Voltmeters measure potential difference
(voltage) and must be connected in parallel.
Ammeters measure current and
must be connected in series.
Photo by Ufbastel on wikipedia
Photo by Christos vittoratos on wikipedia

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Resistance
Resistance is a measure of how much work must be done for charge to flow through a circuit
element and is measured in ohms (Ω) and is equivalent to V·A−1
.
Resistance of circuit elements is related to the material from which they are made as well as
the physical characteristics of length and cross-sectional area.
Photo by Oskay on Flickr

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Resistors in series circuits
Current is constant through resistors in series and they are called voltage dividers as the
sum of the voltages is equal to the voltage across the entire set of resistors.
The total resistance of resistors in series is the sum of the individual resistances.
RS=R1+R2+R3+... V battery=V 1+V 2+V 3+...

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Resistors in parallel circuits
Voltage is constant across resistors in parallel and they are called current divides because
the sum of the current through each is the same as the total current through the circuit
configuration.
The total resistance of resistors in parallel is calculated by using:
V battery=V1=V2=V3=...
1
RP
=
1
R1
+
1
R2
+
1
R3
+...

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