Transcript Ohm’s Law

Electrical Measurement, Ohm’s
Law, & Watt’s Law
CVSD
Electronics 1
Resistance


A measure of the opposition to the flow of
electrons (current) through a material
Unit of Measurement:


Ohm (Ω)
Symbol:

R = Resistance
Current


A measure of the total amount of electrons
flowing in a circuit in a given unit of time
Unit of Measurement:


Ampere (A)
Symbol:

I = Intensity
Voltage


A measure of the Electromotive Force (EMF)
or pressure that pushes electrons through a
circuit
Unit of Measurement:


Volt (V)
Symbol:

E = Electromotive Force
Power


A measurement of the rate of consuming
energy, transferring energy, or doing work
Unit of Measurement:


Watt (W)
Symbol:

P
Ohm’s Law

Describes the mathematical relationship between
resistance, current, and voltage
Voltage (E) = Amperage (I) x Resistance (R)

With two of these values, you can
use Ohm’s Law to find the third
Variations of Ohm’s Law



E = IxR
I = E/R
R = E/I
Ohm’s Law Example



E = 24 VDC
I=?
R = 12 Ω
Calculations
E=IR
24=Ix12
I = 24/12
I=2A
Watt’s Law

Describes the mathematical relationship between
power, current, and voltage
Power (P) = Amperage (I) x Voltage (E)

With two of these values, you can
use Watt’s Law to find the third
Variations of Watt’s Law



P = IE
I = P/E
E = P/I
Watt’s Law Example



P = 36 W
I=?
E = 12 V
Calculations
P=IE
36=Ix12
I = 36/12
I=3W
Combinations of Ohm’s and
Watt’s Laws
Measuring Resistance with the DMM





Must select Ohmmeter Range (Ω)
Pos (+) lead must be in Volt/ Ohm pin
Sat meter to proper range
Must wire in parallel with circuit
Power must be removed from the circuit
Measuring Voltage with the DMM





Must select DC Voltage Range
Pos (+) lead must be in Volt/ Ohm pin
Set meter to proper range
Must wire in parallel with the circuit
Circuit must be have power
Measuring Current with the DMM




Must select DC Current Range
Set meter to proper range. (meter can be damaged if
not set to the proper range)
Must wire in series with the circuit
Circuit must be have power
Measured Tolerance

Predicted values, and measured values
may not always be exactly the same





There is unaccounted for resistance in the wires
etc.
Applied voltage may fluctuate
Human error may disturb measurements
Components have tolerance (not always exact
values)
As components change temperature, resistance
may also change
Review






State Ohm’s Law
State Watt’s Law
How is voltage measured?
How is resistance measured?
How is current Measured?
Why do predicted and calculated values
differ?