Electricity
• An atom consists of a tightly packed nucleus
containing one or more protons (colored red in
the picture), and usually an equal number of
neutrons (yellow). Electrons (blue) surround the
nucleus, forming an electron cloud.
UNIT 01
• The number of electrons in an electrically stable
atom is always equal to the number of protons in
the nucleus.
INTRODUCTION, SAFETY, UNITS and
COMPONENTS
• a proton and an electron are always attracted to
one another, while a proton will repel other
protons, and an electron will repel other
electrons. This behavior is caused by something
called the electric force.
• In a battery, chemical reactions are used to force
electrons from the positive terminal and place
them on the negative terminal.
BASIC UNITS OF ELECTRICITY
• Voltage (Volts): potential or pressure to push electrical charge.
• Current (Amperes): Rate of flow of electrical charge.
• Charge (coulombs): electrons – subatomic particles.
– Atoms: electrons (-ve charge), protons (+ve charge) and neutrons (no
charge)
The amount of overall electric charge possessed by an object is
measured in coulombs. One coulomb is roughly equal to the
amount of charge possessed by 6,000,000,000,000,000,000 (six
billion billion) electrons.
one coulomb is roughly the amount of charge that flows through a
12-watt automotive light bulb in one second.
• The charge on one electron is 1.602x10-19 coulomb
• Resistance/Impedance (Ohms): Difficulty experienced by charge
as it attempts to flow through a circuit.
SAFETY: SHOCK AND FIRE
• Voltage may be dangerous – life threatening
• Shock: path through human body.
– A small flow of electrical current can cause the heart to not operate
properly.
Commercial devices are shielded
No substitute for knowledge
• Fire : Heat generated from current flow through conductor.
– Excessive currents can raise the temperature of a conductor to the
ignition temperature of the insulating material.
– Arc jump across a gap from high voltage to low voltage. Condition of
several thousand degrees.
SAFETY: PROTECTION
SAFETY: STANDARDS AND ORGANIZATIONS
• prevent unsafe electronic equipment from reaching the
general public – formed by manufacturers
• Example: Electronic Industry Association (EIA)
• Manufacturers have products tested by Underwriters
laboratory (UL)
– UL is private service lab - not a government agency
– testing electrical/electronic products for safety
– UL labels on product are important to assure safety
• Occupational Safety and Health Administration (OSHA)
is enforcement arm of the govt
• Standards: written set of recommendations and rules
that define how a technology will operate and includes
safety issues
• Personnel: prevent contact between people and high
voltage
– Enclosures and insulating materials are used
– Energized materials are unaccessible
– Potentially dangerousmade more difficult to access
• Equipment:
– Insulators to protect heat
– Fuses and circuit breakers
– Open circuit and closed circuit
• Other Dangers:
– Electrical and magnetic fields – vicinity of high voltage high
current
– Mobile phones
• Electrical Appliances– stoves, refrigerator 120V Lethal
• Picture tube – 5000V B/W 25000V color
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Conductors, Insulators and Semiconductors
• Conductors:
– materials - electrons move easily, produce easy flow of current.
– copper, aluminum, gold, silver, iron, lead and carbon, some
gases, such as used in fluorescent tubes, and water containing
some chemicals.
Electronic Components – Passive and Active
• Passive – can not amplify or modify shape of signals
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RESISTOR: to intentionally resist the flow of current
POTENTIOMETER; Resistors with variable value
CAPACITORS: store electrical energy in the form of charge
INDUCTORS: stores electrical energy in the form of magnetic field
• Insulators (non-conductors):
– Exchange of electricity is extremely difficult – very high voltage
required
– Rubber, pvc, paper, polysterine, oil
• Semiconductors:
– Compromise between conductors and semi-conductors
– Silicon, germanium
• Active – can amplify or modify shape of signals
– DIODES: allow current to flow in one direction. Two electrical
contacts, AC to DC power supply
– TRANSISTORS: allow control of large current using small current.
Used as switch, amplifiers. Three electrical contacts – one for control
– Complex active devices (integrated circuits): integrate a collection of
other individual components, tens to millions. Number on the
package will indicate the function and content of the package.
RESISTORS
RESISTOR: to intentionally resist the flow of current
– Cylindrical, rectangular.
– Band of colors indicate value of the resistance (ohms)
– Size: power handling capability
CAPACITORS
• CAPACITORS: store electrical energy in the form of charge
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DIODES
• allow current to flow in one direction. Two electrical contacts, AC
to DC power supply
TRANSISTORS
• allow control of large current using small current. Used as
switch, amplifiers. Three electrical contacts – one for control
INTEGRATED CIRCUITS ICs)
• integrate a collection of other individual components
CIRCUIT OARDS
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Basic Structure
Components
Single sides
Double sided
Surface-Mount
Multi-layer
DISPLAY DEVICES
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Light Emitting Diodes (LED)
Liquid Crystal Displays (LCD)
Seven Segment Displays
Switches
CIRCUIT DIAGRAM
• Logical and functional representation of the actual circuit
lamp
lamp
Switch
Battery
Battery
Switch
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The Resistor Color Code
red (2), violet (7), yellow (4 zeros)
and gold bands.
So its value is 270000 = 270 k.
Small Value Resistances
red, violet, gold bands represent 27 × 0.1 = 2.7
blue, green, silver bands represent 56 × 0.01 = 0.56
Voltage
UNIT 1 Lab:
Identification of Components
• Voltage is the electrical force, or "pressure", that
causes current to flow in a circuit. It is measured in
VOLTS (V or E). Take a look at the diagram. Voltage
would be the force that is pushing the water (electrons)
forward.
Current
• Current is the movement of electrical charge - the flow of
electrons through the electronic circuit. Current is measured in
AMPERES (AMPS, A or I). Current would be the flow of water
moving through the tube (wire).
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