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Resistance
and Ohm’s Law
SPH4C
Resistance is the
property of
substances that
impedes the free
flow of electrons.
Resistance
Resistance is the
property of
substances that
impedes the free
flow of electrons.
It is measured in units
of Ohms (W).
Resistance
Loads such as lights and
heating elements have a
resistance: they impede
the flow of electrons and
convert the energy of
electrons into another
form of energy such as
light or heat.
Loads and Resistance
A resistor is a load
placed in a circuit
simply to impede the
flow of electrons and
thus control the
current to the rest of
the circuit.
Resistors
The resistance of
a resistor is
typically
indicated by
colour-coded
bands:
Resistors and Resistance
The resistance of
a resistor is
typically
indicated by
colour-coded
bands:
Resistors and Resistance
The resistance of
a resistor is
typically
indicated by
colour-coded
bands:
Resistors and Resistance
The resistance of
a resistor is
typically
indicated by
colour-coded
bands:
Resistors and Resistance
The current that flows through a resistor
will be equal to:
V
I
R
Resistance and Current
The current that flows through a resistor
will be equal to:
V
I
R
This is called Ohm’s Law and often written:
V  IR
Resistance and Current
If a 50-W resistor is connected to a 1.5 V
battery, what is the current through the
resistor?
Example
If a 50-W resistor is connected to a 1.5 V
battery, what is the current through the
resistor?
R  50 W
V  1. 5 V
I ?
Example
If a 50-W resistor is connected to a 1.5 V
battery, what is the current through the
resistor?
R  50 W
V  1. 5 V
I ?
Example
V
I
R
1.5V
I
 0.03 A
50 W
or 30 mA
If a 50-W resistor is connected to a 1.5 V
battery, what is the current through the
resistor?
R  50 W
V  1. 5 V
I ?
Example
V
I
R
1.5V
I
 0.03 A
50 W
or 30 mA
If a 50-W resistor is connected to a 1.5 V
battery, what is the current through the
resistor?
R  50 W
V  1. 5 V
I ?
Example
V
I
R
1.5V
I
 0.03 A
50 W
or 30 mA