Transcript Ohms Law Ohmic Resistors versus Lightbulbs

Ohms Law
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Ohm’s Law
Ohm's law is the most important, basic law of
electricity. It defines the relationship between
the three fundamental electrical quantities:
current (I), voltage (V), and resistance (R).
Ohm’s Law
The mathematical equation that shows the
relationship between electric voltage, current
and resistance. Ohm’s Law was named after
Bavarian mathematician and physicist Georg
Ohm.
Ohm’s Law
When a voltage is applied to a circuit
containing only resistive elements (i.e. no
coils), current flows according to Ohm's Law.
V=IR
Ohm’s Law
Ohm's law states that the electrical current (I)
flowing in an circuit is proportional to the
voltage (V) and inversely proportional to the
resistance (R).
Ohm’s Law
In other words, if the voltage is increased, the
current will increase provided the resistance
of the circuit does not change.
Linearity of Voltage and Current for
Resistors which Obey Ohm’s Law
Current (A)
Voltage versus Current
for a 10 ohm Resistor
0.6
0.5
0.4
0.3
0.2
0.1
0
0
1
2
3
4
5
6
Voltage (V)
Voltage and current are linear when resistance is held constant.
Ohm’s Law
Example:
If the circuit has a 100 Ohm resistor and the
voltage is increased from 12 Volts to 24
Volts, the current will increase. Likewise if the
voltage is drop from 24V to 12V, the current
will decrease.
Ohm’s Law
Similarly, increasing the resistance of the
circuit will lower the current flow if the voltage
is not changed.
Ohm’s Law
Example:
If the circuit has a 12V supply and the
resistance is increased from 100 Ohms 200
Ohms, the current will decrease. Likewise if
the resistance is reduced from 200Ohms to
100Ohms, the current will increase.
Ohm’s Law
The formula can be reorganized so that the
relationship can easily be seen for all of the
three variables.
Ohm’s Law
Exercise:
Verify Ohms Law by substituting values in
each equation below.
V=IxR
R=V/I
I=V/R
Ohm’s Law
It should be evident that knowing any two of
the values of a circuit, one can determine the
third using Ohm’s Law.
V=IxR
R=V/I
I=V/R
Ohm’s Law
Another useful equation to know is the power
equation:
P = E*I
(power equals voltage multiplied by current
or watts = volts * amps).
Ohm’s Law
From this we can substitute Ohm's law for
any values we don't know. For instance if we
need to know power but we only have
amperage (I) and resistance (R) then we
could substitute I*R in the power equation
(because according to Ohm's law E=I*R) and
get P = I*R*I.
Ohm’s Law
Now that we have established a direct
relationship with Power, Voltage, Current and
Resistance, knowing any two of the values of
a circuit, one can determine the third and
fourth values using Ohm’s Law and the
Power Formula.
Ohm’s Law
This graphic is a good tool to use for solving any number of combinations of Ohms
Law.
Experiment 1
One 10 ohm resistor connected to the battery.
Connect a second 10Ω resistor in parallel to the
first one
Q:
What will the new resistance be? What will
happen to the current through each resistor and
the voltage across each component of the
circuit?
Conclusion
V = I x R Ohms Law
P = I x V Power Formula
End of Presentation