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Ohm’s Law
The most important fundamental law
in electronics is Ohm’s law, which
relates voltage, current, and
resistance.
Georg Simon Ohm (1787-1854) studied
the relationship between voltage,
current, and resistance and formulated
the equation that bears his name.
Summary
Review of V, I, and R
Voltage is the amount of energy per charge available to
move electrons from one point to another in a circuit.
Current is the rate of charge flow and is measured in
amperes.
Resistance is the opposition to current and is measured
in ohms.
SI unit for voltage is volts (v)
SI unit for current is amps (A)
SI unit for resistance is ohms (Ω)
If you need to solve for current, Ohm’s law is:
V
I
R
What is the current in from a 12 V source if the
resistance is 10 W? 1.2 A
If you need to solve for voltage, Ohm’s law is:
V  IR
What is the voltage across a 680 W resistor if the
current is 0.25 A?
170 V
If you need to solve for resistance, Ohm’s law is:
What is the resistance of
the bulb? 132 W
V
R
I
OFF
V
Hz
115
V
V
mV
A
Range
Autorange
Touc h/Hold
1s
1s
10 A
V
40 mA
COM
Fused
Practice

What value of resistor would be used to permit a
current of 0.2 A to flow using a 6V supply?
R=V/I

R=30Ω
Calculate the voltage across a 300 ohm resistor
when a current of 0.004 A flows through it.
V=IR

R=6/0.2
V=(0.004)(300)
V=1.2V
A resistor allows a current of 0.6 A to flow when
connected to a 9.6 volt supply.
What current would flow if the same resistor
was connected to a 12.8 V supply?
R=V/I
I=V/R
R=9.6/0.6
I=12.8/16
R=16Ω
I=0.8 A