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Basic Electrical Theory
• Voltage and Current
•
Voltage
W
V
Q
• The difference in potential energy per charge in electrical
terms is called voltage
• Voltage is defined as energy or work (W) per unit charge (Q).
• W is expressed in joules (J) and Q is in coulombs (C)
• Where joule is the energy measurement
2
kg

m
m
for a unit of work
J  Nm  2  m  kg 2
s
s
• Example
• If 50 J of energy are available for every 10 C of charge,
what is the voltage?
W 50 J
V 
 5V
C 10C
Basic Electrical Theory
• Voltage and Current
•
Current
• 6.25 X 1018 electrons passing a point in a wire in
one second due to a difference of potential at the
two ends is a current of one ampere (1A)
• One coulomb: the total charge possessed by 6.25 X
1018 electrons
• A single electron has a charge of 1.6 X 10-19 C
•
Power
• The voltage across a device times the current
through the device equals the power being used as
measured in Watts
Basic Electrical Theory
• Voltage and Current
•
Resistance
• Resistance is the opposition to current
• One ohm (1) of resistance exists if there is one
ampere (1A) of current in a material when one volt
(1V) is applied across the material
•
Impedance
• Resistance is a critical component of impedance
and in AC circuits.
• It’s effect doesn’t very with frequency of the AC voltage
Basic Electrical Theory
• Voltage and Current
•
Impedance
• Capacitive and Inductive Reactance
• As the frequency of the signal decreases the value of
capacitive reactance increases and it has a bigger effect
on the impedance to an AC signal
• As the frequency of the signal increases the value of
inductive reactance increases and it has a bigger effect
on the impedance to an AC signal
•
Resistance
• One ohm (1) of resistance exists if there is one ampere (1A)
of current in a material when one volt (1V) is applied across
the material
Basic Electrical Theory
• Voltage and Current
•
Impedance
• Resistance is a critical component of impedance and in AC
circuits.
• It’s effect doesn’t very with frequency of the AC voltage
• Capacitive and Inductive Reactance
• As the frequency of the signal decreases the value of capacitive
reactance increases and it has a bigger effect on the impedance
to an AC signal
• As the frequency of the signal increases the value of inductive
reactance increases and it has a bigger effect on the impedance
to an AC signal
• Voltage, Resistance, and Current
•
•
Ohm’s Law Link
Example of Relationship Link