Transcript Ohm`s Law - panthertech

Ohm’s Law
Ohm’s Law
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Georg Ohm
Ohm’s Law
Ohm’s Law Chart
Ohm’s Law Practice
This presentation is intended to be used with Activity 6.2.4 Ohm’s Law.
Georg Ohm
Georg Simon Ohm 1789-1854
German Physicist / School
Teacher
Discovered the mathematical
relationship between current,
voltage, and resistance
Ohm’s Law
If you know 2 of the 3 quantities, you can solve for the third.
Quantities
Abbreviations
Units
Label
Voltage
V or E
Volts
V
Current
I
Amperes
A
Resistance
R
Ohms
Ω
V=IR
I=V/R
R=V/I
Ohm’s Law Chart
Cover the quantity that is unknown.
V
I xR
Solve for V
V=IR
Ohm’s Law Chart
Cover the quantity that is unknown.
V
I R
Solve for I
I=V/R
Ohm’s Law Chart
Cover the quantity that is unknown.
V
I R
Solve for R
R=V/I
New Prefixes
mA
Milliamp = 0.001 amps
KΩ
Kilo ohm = 1000 ohms
When making circuit measurements, it is
important
to always work
Equivalent
The Equivalent
Unitsinare…
Units.
KΩ
V
mA
OR
Ω
V
A
For our lab, we will be using
V, KΩ and mA.
Your Turn!
V
I R
V
mA KΩ
V
A
Ω
Remember our Multimeter?
Let’s look at how they are used to
measure variables in Ohm’s Law.
Measuring Voltage
Measure across a component.
Switch
Battery
Resistor
Light
Measuring Current
Circuit flow must go through the meter.
Switch
Battery
Resistor
Light
Measuring Resistance
Measure across the component being tested.
Power must be off or removed from the circuit.
Switch
Battery
Resistor
Light
Now Back to Ohm’s Law
Ohm’s Law Practice
Create a series circuit with a DC source and the two
supplied fixed resistors with the color bands visible.
Calculating Resistance
• Power the circuit and use a multimeter to
measure the voltage drop across each fixed
resistor. Add those values to get the total
voltage. Record that value on your activity
page, using volts for your units.
• Remove one of the connectors and measure
the current with the power on. Record that
value on your activity page, using mA
(milliamps) for your unit.
DC
Ohm’s Law Practice
Calculating Resistance
•
Use Ohm’s Law to calculate the total resistance
delivered by the fixed resistors. Record that value on
your activity page. KΩ will be your measurement unit.
•
Remove the fixed resistors from the circuit and
determine the value of each using the color bands. Add
the values together. Record that total value on your
activity page. KΩ will be your measurement unit.
How close were the calculated and color band
resistance values?
DC
Ohm’s Law Practice
Create a series circuit with a DC source and fixed
resistors V1 and V2.
Calculating Voltage
•
With the power off, use the multimeter to measure the
resistance of each fixed resistor. Total resistance will be
the sum of each of the measured resistances. Record
the resistances, and their sum, on your activity page.
KΩ will be your measurement unit.
•
Remove one of the connectors and measure the current
with the power on. Record that value on your activity
page. mA will be your measurement unit.
DC
Ohm’s Law Practice
Calculating Voltage
•
Use Ohm’s Law to calculate the voltage of the circuit.
Record that value on your activity page. V (volts) will
be your measurement unit.
•
Power the circuit and use a multimeter to measure the
voltage drop across each fixed resistor. Add those
values to get the total voltage. Record the total voltage
on your activity page. mA will be your measurement
unit.
How close were the calculated and measured voltage
values?
DC
Ohm’s Law Practice
Create a series circuit with a DC source and fixed
resistors C1 and C2.
Calculating Current
•
•
With the power off, use the multimeter to measure the
resistance of each fixed resistor. Total resistance will be
the sum of each of the measured resistances. Record
the resistances, and their sum, on your activity page.
KΩ will be your measurement unit.
Power the circuit and use a multimeter to measure the
voltage drop across each fixed resistor. Add those
values to get the total voltage. Record that value on your
activity page. V (volts) will be your measurement unit.
DC
Ohm’s Law Practice
Calculating Current
•Use Ohm’s Law to calculate the current of the circuit.
Record that value on your activity page. mA will be your
measurement unit.
•Remove any one connection and measure the current.
Record that value on your activity page. mA will be your
measurement unit.
How close were the calculated and measured current
values?
DC
Answer the conclusion
questions on your Activity
Sheet!
Image Resources
Microsoft, Inc. (2009). Clip Art. Retrieved January 13, 2009, from
http://office.microsoft.com/en-us/clipart/default.aspx