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Voltage in Electrical
Notes (p71)
Electrical systems comprise:
4 basic components:
• Voltage sources (batteries and generators)
• Control elements (switches)
• Electrical appliances or loads (lights, heaters,
computers, motors etc)
Conductors (copper wire)
Types of electricity
Direct current (DC)
Alternating current (AC)
• Electric charge in wires moves one way only
• DC is produced by batteries, or generators
• Electric charge moves back and forth in the wire
many times per second
AC is produced by alternators
Current is the movement of electric charge
and is measured in amperes or amps
Voltage is measured in volts
DC Supplies I
Batteries are a source of chemical energy which
is converted into electrical energy when the
battery is placed in a circuit.
• Dry cells
• contain a paste electrolyte
• D, AAA, AA
• voltages can be 1.5V, 3V, 6V, 9V
• composition can be carbon-zinc, Ni-Cad, Li-Ion
• Wet cells
• contain a liquid electrolyte
• Auto batteries (lead-acid)
• Cell voltages can be 2V
Recharging capability
Pumping weak current into the battery in the opposite
direction from a battery charger
Wet cells and some dry cells can be recharged from a
“dead” state
Primary cells
• Difficult to recharge
• Secondary cells
• Easily recharged
How are DC Voltage sources
Connection options
Batteries have terminals or electrodes
Terminals are positive (anode) and negative (cathode)
When connected into a circuit electrons flow from the
negative electrode to the positive electrode.
Series connection of batteries
the positive terminal of one battery is connected to the negative
terminal of another battery, providing a net voltage that is the sum
of both batteries.
What makes up a DC circuit?
The following components:
• Source
• Conductors
• Control
• Load
This circuit can be shown in schematic
form with symbols representing the
components above, as on next …
What makes up a DC circuit?
Voltage - a “forcelike” quantity
(prime mover)
In all electrical systems, voltage acts like a force,
moving electricity, or negative charges, through the
The atomic structure underpins the electricity model
in that each atom comprises:
Nucleus with
Surrounding the nucleus are
• Protons (+ve),
• Neutrons (neutral), and
• Most of the atomic mass
• Electrons (-ve)
Electrical forces create a voltage difference
whenever the positive and negative charges are
How can a voltage difference be
Chemical – dry & wet cell batteries
Magnetic/mechanical – a coil of wire
moving in a magnetic field produces a force
on electrical charges that separates the
positive and negative charges.
Light – photoelectric effect in which
incident light falling on some substances
causes the separation of electrons from
their atoms resulting in a movement of
charges (or current).
• Example – photocell
How are voltages measured?
The difference in voltage between any 2
points in a circuit is measured with a
voltmeter in units of volts, millivolts,
A voltmeter can be of many types, such as:
• Analog
• Digital
• Oscilloscope
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