BASIC ELECTRONICS
THE VOLT: UNIT OF POTENTIAL
DIFFERENCE
Potential refers to the possibility of
doing work.
The Volt Unit
The volt unit of potential difference is named
after Alessandro Volta (1745–1827).
The volt is a measure of the amount of
work or energy needed to move an
electric charge.
The Volt Unit
The metric unit of work or energy is the joule
(J).
1 𝐽𝑜𝑢𝑙𝑒 = 0.7376 𝑓𝑡. 𝑙𝑏.
1𝐽
1𝑉 =
1𝐶
The Volt Unit
In electronics, potential difference
commonly referred to as voltage, with the
symbol V .
𝑊
𝑉=
𝑄
Where,
𝑉 = 𝑣𝑜𝑙𝑡𝑎𝑔𝑒 𝑖𝑛 𝑣𝑜𝑙𝑡𝑠
𝑊 = 𝑤𝑜𝑟𝑘 𝑖𝑛 𝑗𝑜𝑢𝑙𝑒𝑠
𝑄 = 𝑐ℎ𝑎𝑟𝑔𝑒 𝑖𝑛 𝑐𝑜𝑢𝑙𝑜𝑚𝑏𝑠
is
Practice Problem 1
What is the output voltage of a battery that
expends 3.6 J of energy in moving 0.5C of
charge?
Practice Problem 2
If 27 J of energy is expended in moving 3 C of
charge between two points, how much
voltage is there between those two points?
CHARGE IN MOTION IS CURRENT
When the potential difference between
two charges forces a third charge to
move, the charge in motion is an
electric current.
To produce current, therefore, charge
must be moved by a potential
difference.
Charge in Motion is Current
The current is a continuous flow of
electrons. Only the electrons move, not
the potential difference.
The Ampere of Current
The unit for stating the amount of
current is defined in rate of flow of
charge. When the charge moves at the
18
rate of 6.25 × 10
electrons flowing
past a given point per second, the
value of the current is one ampere (A).
The Ampere of Current
The ampere unit of current is named
after André M. Ampère (1775–1836).
The symbol for current is I or i for
intensity, since the current is a
measure
of
how
intense
or
concentrated the electron flow is.
How Current Differs from Charge
Charge is a quantity of electricity
accumulated in a dielectric, which is an
insulator.
The
charge
is
static
electricity, at rest, without any motion.
When the charge moves, usually in a
conductor, the current I indicates the
intensity of the electricity in motion.
How Current Differs from Charge
This characteristic is a fundamental
definition of current:
𝑄
𝐼=
𝑇
where,
𝐼 = 𝑐𝑢𝑟𝑟𝑒𝑛𝑡 𝑖𝑛 𝑎𝑚𝑝𝑒𝑟𝑒𝑠
𝑄 = 𝑐ℎ𝑎𝑟𝑔𝑒 𝑖𝑛 𝑐𝑜𝑢𝑙𝑜𝑚𝑏𝑠
𝑇 = 𝑡𝑖𝑚𝑒 𝑖𝑛 𝑠𝑒𝑐𝑜𝑛𝑑𝑠
Practice Problem 3
The charge of 12 C moves past a given point
every second. How much is the intensity of
charge flow?
Practice Problem 4
The charge of 5 C moves past a given point
in 1 s. How much is the current?
Practice Problem 5
A dielectric connected to conductors with a
current of 0.4A. If the current can deposit
electrons for 0.2s, what is the accumulated
charge in the dielectric?
RESISTANCE IS OPPOSITION TO
CURRENT
The opposition which limits the amount
of current that can be produced by the
applied voltage, is called resistance.
The Ohm
The practical unit of resistance is the
ohm.
The ohm unit is named after Georg
Simon Ohm (1787–1854), a German
physicist.
The Ohm
The symbol for resistance is R.
The abbreviation used for the ohm unit
is the Greek letter omega, written as Ω.
Conductance
The
opposite
conductance.
of
resistance
is
Its symbol is G, and the unit is the
siemens (S), named after Ernst von
Siemens
(1816–1892),
a
German
inventor.
Conductance
G is the reciprocal of R.
1
1
𝐺 = also 𝑅 =
𝑅
𝐺
Practice Problem 6
Calculate the resistance for the following
conductance values:
(a) 0.05S
(b) 0.1S
Practice Problem 7
Calculate the conductance for the following
resistance values:
(a) 1kΩ
(b) 5kΩ