Science Olympiad Shock Value & Circuit Lab Workshop

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Transcript Science Olympiad Shock Value & Circuit Lab Workshop

Delaware
Science Olympiad
Shock Value & Circuit Lab
Workshop
Delaware Bay Section
1
Instructors and contacts
Gordon Lipscy - [email protected]
 Wayne Lu - [email protected]

7/17/2015
2
Science Olympiad Competitions

Division B


Middle School
Shock Value
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Division C

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High School
Circuit Lab
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DC Circuit Theory, Electrical Device Concepts, Circuit Construction
and Analysis, Magnetism, Magnetic Application
Historical Items, SI Units,
All Division B concepts, plus, Digital Logic
Both Events have the same format:

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7/17/2015
50 - 75% written test
25 - 50% hands-on lab experiment
3
IEEE
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IEEE, read I-triple-E
The largest professional association in the world
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Institute of Electrical and Electronic Engineers
425,000 members in 160 countries
Formed in 1963 by the merger of IRE (1912) and AIEE (1884)
Notable past presidents of IEEE and its founding organizations:
Elihu Thomson – co-founder of Thomson-Houston Electric Co. which eventually
became General Electric Company (GE)
 Alexander Graham Bell (AIEE) – inventor of telephone
 William R. Hewlett (IRE) – co-founder of Hewlett-Packard Company (HP)
 Ivan A. Getting – contributed to development of GPS
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IEEE Standards

IEEE standards affect a wide range of industries, including power, energy,
biomedical and healthcare, information technology, telecommunications,
transportation, nanotechnology and many more.
 In 2013, IEEE has over 900 active standards
 One notable IEEE standard is IEEE802 LAN/MAN group of standards
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IEEE 802.3 Ethernet standard – governs data communications
IEEE 802.11 Wireless Network standard – WiFi as commonly called.
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Brief History of Electricity (1)

Electricus – “like amber” in Greek
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Charles-Augustine de Coulomb (1736-1806)
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Ampere’s circuital law determines the relationship between electrical current and magnetic
field
Ampere (A) – SI unit for electrical current
Michael Faraday (1791-1867)
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Invented battery and means to study electrical potential and charge
Volt (V) – SI unit for electrical potential (voltage)
Andre-Marie Ampere (1775 – 1836)
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Discovered lightning was electrical in nature
Alessandro Volta (1745-1827)
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Coulomb’s Law – “like-charged objects repel and opposite-charged objects attract
Coulomb (C) – SI unit for electric charge
Benjamin Franklin (1706 – 1790)
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Refer to the amber’s property of attracting small object after being rubbed
Discovered electromagnetic induction, diamagnetism (superconductor) and electrolysis
Farad (F) – SI unit for capacitor
Joseph Henry (1797-1878)
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Discovered electromagnetic induction independently of Michael Faraday
Invented the electric door bell.
Henry (H) – SI unit of inductance
SI - International System of Units
cgs – centimeter, gram and second
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Brief History of Electricity (2)

Georg Ohm (1789-1854)
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James Clerk Maxwell (1831 – 1879 )
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Ohm’s law – direct proportionality between the potential difference (voltage) applied to a
conductor and the resultant electric current
Ohm (Ω) – SI unit for electrical resistance
Unified Electricity, Magnetism and Light (Electromagnetic Theory of Light)
Johann Carl Friedrich Gauss (1777-1855)
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German mathematician and physical scientist contributed significantly to many fields
including number theory, algebra, statistics, analysis, differential geometry, geodesy,
geophysics, electrostatics, astronomy and optics
Gauss Law of Magnetism
His student, Gustav Kirchhoff, discovered Kirchhoff’s circuit laws
Gauss (G) – cgs unit for a magnetic field, magnetic flux density
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Heinrich Rudolf Hertz (1857-1894)
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SI unit for magnetic field is Tesla, named after Nikola Tesla
Proved existence of electromagnetic waves and the electromagnetic waves can travel over
distance in space
Hertz (Hz) – SI unit for frequency, or circle per second
Albert Einstein (1879- 1955)
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Won Nobel Prize for his work on photoelectric effect
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not for Theory of Relativity
Photoelectric effect is used in photocell, solar panels
SI - International System of Units
cgs – centimeter, gram and second
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Electrical Safety (Static Electricity)
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Sources - friction between materials including clouds
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Characteristics - 30,000 volts per centimeter of air gap,
ionization of air = spark, current levels can be huge
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Hazards - Shock/burns, power line surges harm motors,
destruction of microelectronics can occur from clothes or
carpet static
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Electrical Safety (Alternating Current = AC)
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Sources - rotating generators in power plants (mechanical to
electrical) & inverters (DC to AC)
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Characteristics - sine wave with frequency and amplitude, ease of
generation, ease of voltage transformation, easy arc suppression
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Hazards - heart fibrillation from milliamp currents (120 volt
household power can be deadly), shock/burns, downed wires,
insulation breakdown from moisture, contamination or abrasion
(frayed cords), outlets, portable appliances, contact resistance
(burns/fires)
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AC Circuits are not covered in the Science Olympiad events
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Electrical Safety (Direct Current = DC)
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Sources - batteries (chemical to electrical), rotating alternators and
generators (mechanical to electrical), solar panels (light to
electrical), fuel cells (chemical to electrical), piezoelectric (heat to
electrical), power supplies (AC to DC), solar wind (ions moving
through space -northern lights)
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Characteristics – By convention, current flows from (+ ) to (-)
[flow of holes], no easy voltage transformation, arcs difficult to
suppress.
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Hazards - high voltage shock/burns, low voltage/high current
burns/welding [car batteries] , no switch at some sources [solar
panels]
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Magnets
- Properties
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2 Poles – The pole of a magnet which is attracted to the earth’s
North pole is defined as the North pole of that magnet, the other
pole being South.
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Like poles repel each other, unlike poles attract.
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Three types of magnets: naturally occurring, man-made &
electromagnets.
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The direction of magnetic lines of force is defined as coming out of
the North pole and going into the South pole.
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Bar magnet lines of force
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Electromagnetism
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Electrical coil or solenoid magnetic field – Right hand rule
1. Current coming out of page at
top (head of arrow).
2. Current going into page at bottom
(crossed feathers on arrow).
3. With fingers wrapped in direction of
current, outstretched right thumb points in
direction of induced magnetic field.
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Electrical coil magnetic lines of force
Force from current in a magnetic field -
Force = V X B
where: V is the velocity vector of the moving charge
X is the cross operator for vectors and
B is the magnetic field vector
This is a second right hand rule – All fingers initially point in direction of V and then
bend to direction of B. Outstretched right thumb points to direction of force, F.
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Basic Circuit Theory – Electric Charge
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Charge is an electrical property of the atomic particles of which
matter consists, measured in coulombs (C).
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The charge e on one electron is negative and equal in magnitude to
1.602 ×10-19 C which is called as electronic charge. The charges
that occur in nature are integral multiples of the electronic charge.

Before electrons were discovered, experiments in electrolysis
suggested a current that moved bit of metal from one electrode to
another. That current, which is basically the movement of positive
ions, led to the electrical convention of current being the flow of
positive charge.
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Basic Circuit Theory – Electric Current (1)
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Electric Current (I) is a flow of electric charge. In electric circuit. This charge is often
carried by moving electrons in a wire. It can be carried by ions in an electrolyte (like
battery), or by both ions and electrons such as in a plasma.
The unit of ampere can be derives as 1A = 1C/s
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C – Coulomb,
s – second
Electric Current is measured by an Ampere Meter.
A direct current (DC) is a current that remains constant with time
An alternating current (AC) is a current that varies sinusoidally with time
Current flows in the same direction as positive ions but the opposite direction as
negative ones.
Positive Ions
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Negative Ions
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Basic Circuit Theory – Electric Current (2)
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Example 1
A conductor has a constant current of 5A
How many electrons pass a fixed point on the conductor in one minute?
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Solution
Total number of charges pass in 1 min is given by
5A = (5C/s)*(60 s/min) = 300 C/min
Total number of electrons pass in 1 min is given by
300 C/min / 16.02 x 10-19 C/electron) = 1.87 x 1021 electrons / min
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Basic Circuit Theory – Electric Voltage
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Voltage (potential difference) is the energy required to move a unit
charge through an element, measured in volts(V)
Voltmeter measures voltage
Electric Voltage (V) is always across the circuit element or between
two points in a circuit

Vab > 0 means the potential of a is higher than the potential of b
 Vab <0 means the potential of a is lower than the potential of b
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Basic Circuit Theory – Power Energy
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Power (p) is the time rate of expending or absorbing energy measured
in Watt (W)
Mathematical Expression:
p=v*i
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p is the power,
v is the voltage (potential difference) across the circuit element
i is the electric current flow through the circuit element
Law of conservation of energy
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The sum of total power supplied and absorbed by the elements in a
completed circuit is ZERO
p = + v*i
p = - v*i
Absorbing power
Supplying power
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Basic Circuit Theory – Circuit Elements
Independent
sources
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Dependent
sources
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Basic Circuit Theory – Ohm’s law
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Voltage (V) across a resistor is directly proportional to the current (I)
flowing through the resistor.
Mathematical express:
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R = Resistance
Two extreme possible value of R:
0 (zero) and ∞ (infinite)
are related with two basic circuit concepts:
short circuit and open circuit
Ohm meter is to measure resistance
The power dissipated by a resistor
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V=I*R
P = V*I = I2 * R = V2/R
The power dissipated in resistors is typically converted to heat
and/or light as in light bulbs.
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Basic Circuit Theory – Branches, Nodes, Loops
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A Branch represents a single element such as a voltage source or a
resistor
A node is the point of connection between two or more branches
A loop is any closed path in a circuit
Original circuit
Network schematics
or graph
It has 5 branches, 3 nodes, 6 loops
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Basic Circuit Theory – Kirchhoff Current Law (1)
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The algebraic sum of currents entering a node (or a closed
boundary) is zero
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Basic Circuit Theory – Kirchhoff Current Law (2)
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Determine the current I for the circuit shown in the figure
I + 4 –(-3) -2 = 0
-3A
2A
4A
I = -5A
I
This indicates the actual current for I
is flowing in the opposite direction
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Basic Circuit Theory – Kirchhoff Voltage Law (1)
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The algebraic sum of all voltages around a closed path (or loop) is
zero
V1 + V2 + V3 + V4 + V5 = 0
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Basic Circuit Theory – Kirchhoff Voltage Law (2)
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Applying the KVL equation for the circuit of the figure below
Va –V1-Vb-V2-V3 = 0
V1 =I*R1
V2 =I*R2
V3=I*R3
Va-Vb = I * (R1+R2+R3)
I = (Va-Vb)/(R1+R2+R3)
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Basic Circuit Theory – Series Circuit
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Series: Two or More elements are in series if they are cascaded or
connected sequentially and consequently carry the same current
The equivalent resistance of any number of resistors connected in a
series is the sum of the individual resistances
Req = R1 + R2 + R3 + … + Rn
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Basic Circuit Theory – Parallel Circuit
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Parallel: Two or More elements are in parallel if they are connected to the same
two nodes and consequently carry the same voltage across them
The equivalent resistance of any number of resistors connected in a series is the
sum of the individual resistances
1
1 1 1
1
    ... 
Re q R1 R2 R3
Rn
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Basic Circuit Theory – Example
10V and 5 Ω are
in series
2A, 2 Ω and 3 Ω
are in parallel
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Basic Circuit Theory – Superposition Theorem
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The principle of superposition helps us to analyze a linear circuit with
more than one independent source by calculating the contribution of each
independent source separately.
Superposition Theorem:
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Voltage across (or current through) an element in a linear circuit is the
algebraic sum of the voltage across (or currents through) that element due to
EACH independent source acting alone
We consider the effects of the 8A and 20V source one by one , then add
the two effects together for final V0
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Basic Circuit Theory – Superposition Theorem
Turn off all independent sources except one source. Find the output
(voltage or current) due to that active source
1.

When we say turn off all other independent sources:


2.
3.
Independent voltage sources are replaced by 0V (short circuit)
Independent current sources are replaced by 0A (open circuit)
Repeat step 1 for each of the other independent sources
Find the total contribution by adding algebraically all the contributions
due to the independent sources
3A is discarded
by open circuit
Answer: V = 10V
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6V is discarded
by short circuit
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Basic Circuit Theory – Norton Equivalents (1)
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Norton equivalent circuit is used for circuit analysis, simplification
and to study circuit’s initial condition and steady state response
To find the equivalent:

Find the Norton current INO. Calculate the output current IAB, with a
short circuit as the load (meaning 0 resistance between A and B). This
is INO
 Find the Norton resistance RNO. When there is no dependent source
(all current and voltage sources are independent), there are two
methods of determining the Norton resistance
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Calculating the output voltage VAB, when in open circuit condition, RNO =
VAB/INO
Replace independent voltage sources with short circuits and independent
current sources with open circuits. The total resistance across the output
port is the Norton resistance RNO
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Basic Circuit Theory – Norton Equivalents (2)
Original circuit
Calculating the
equivalent output
current
Calculating the
equivalent
resistance
Norton equivalent circuit
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Basic Circuit Theory – Thevenin Equivalents (1)
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Similar to Norton equivalent circuit, Thevenin equivalent circuit is
used for circuit analysis, simplification and to study circuit’s initial
condition and steady state response
To find the equivalent:
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Find the output voltage VAB. When in open circuit condition (no load
resistor – meaning infinite resistance). This is VTh,
Find the the output current IAB, when the output are short circuited
(load resistance is 0). RTh = VTh/IAB
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Basic Circuit Theory – Thevenin Equivalents (2)
Original circuit
Calculating the
equivalent output
voltage
Thevenin equivalent
circuit
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Calculating the
equivalent
resistance
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Capacitor

A capacitor is a passive two-terminal electrical device used to store energy electrostatically
in an electric field. It contains:
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Two electrical conductors and
An insulator called dielectric separates the two conductors
When there is a potential (voltage) different across the two conductors, an electrical field
develops across the dielectric, causing positive charge to collect on one plate and negative
charge on the other plate. Energy is stored in the electrostatic field.
An ideal capacitor is characterized, or described, by a single constant value, capacitance.
Capacitance is the ratio of the electric charge on each conductor to the voltage potential
between them
The SI unit of capacitance is the Farad – Named after Michael Faraday
Q (Coulomb )
C ( Farad ) 
V (Volt)
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RC Circuits (1)
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RC Circuit consists of a resistor and a capacitor. It is one of the simplest forms of
analog circuit.
Vc  Vc 0  e
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
t
(
)
RC
If the capacitor is charged up, there are charges (q) stored in the capacitor.
When switch is closed, the charges (q) in the capacitor start to leak out. The
movement of the charges is the current (Idischarging)
When the capacitor losses charge (or discharges), the voltage of the capacitor
drops as the result.
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RC Circuits (2)
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The capacitor voltage will drop following the equation.
The product of RC is called RC time constant.
The RC constant determines the rate of discharging or charging (if the capacitor
is being charged)
When the time reaches 1x of time constant, the capacitor lost about 63% of its
original charge.
Vc  Vc 0  e
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(
t
)
RC
35
Wheatstone Bridge
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A Wheatstone Bridge is an electrical circuit used to measure an unknown electrical resistance
by balancing two legs of a bridge circuit.
It was invented by Samuel Hunter Christie in 1833 and improved by Sir Charles Wheatstone.
In a Wheatstone Bright:
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One leg of the bridge includes the unknown component Rx.
The other 3 resistors’ resistances are known.
R2 resistance is adjustable
If R2 is adjusted so that the ratio of R1 and R2 equals to the ratio of R3 and Rx, the voltage
between nodes B and D becomes zero. No current flows between B and D.
The Zero current can be measured with extremely high precision.
If R1, R2 and R3 values are known to very high precision, Rx can also be measured in very
high precision.
R1 R3

R 2 Rx
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R2
Rx  R3 
R1
36
Basic Circuit Theory – Electronic Color Code

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The electronic color code is used to indicate the values or ratings of
electronic components, very commonly for resistors, but also for capacitors,
inductors, and others.
A separate code, the 25-pair color code, is used to identify wires in some
telecommunications cables.
Don’t try to memorize it unless you
are truly and utterly bored!
Ask Google instead.
With the advances in technology, resistor sizes
have shrunk enormously from their original
size, and Surface Mount Device (SMD) or
chip resistors are now being used in vast
quantities by equipment manufacturers.
These really are tiny by comparison which
makes the use of color coding impractical,
not only from a manufacturing point of view,
but also for the poor end user who's got to
try and read them!
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Multimeter 1.01
Metric units
Electrical potential = volts (v),
Electrical current = amperes or
amps(a)
Electrical resistance = ohms (Ω)
Electrical power = watts (w)
Electrical energy = watt hours (wh)
Metric prefixes:
Mega (M)= 1,000,000 or 106
kilo (k)=1,000 or 103
milli (m) = 1/1,000 or 10-3
micro (µ) = 1/1,000,000 or 10-6
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Multimeter 1.02

Measuring resistance - Ensure circuit deenergized, test leads in
COM & VΩmA jacks, start at highest Ω setting on meter and reduce
until most accurate reading is obtained. CAUTION: internal
resistance of the meter in Ω settings is very low and any voltage in
the circuit may damage the meter.

Measuring DC voltage - This is the safest measurement to be made
on an energized circuit since the internal resistance of the meter in
any DCV setting is near infinite: however, you should always select
the highest voltage setting that you might expect in the circuit and
reduce the range setting to get the most accurate reading. If you
always use the convention of putting the BLACK test lead in the
COM jack and the RED lead in the VΩmA jack, the meter will then
always show the voltage at RED minus the voltage at BLACK (the
voltage difference). If the reading is negative, the voltage at BLACK
is higher than at RED.
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Multimeter 1.03

Measuring DC current - CAUTION: internal resistance of the meter
in DCA settings is close to zero and any voltage applied directly to
the meter will most likely damage the meter. Rather than using this
capability of the multimeter, it is recommended that you measure the
voltage across a resistor in the circuit and use Ohm's law to
determine the current or install a low resistance into the circuit and
then measure the voltage drop to calculate the current.

Measuring AC voltage - No AC circuits are used in the Science
Olympiad and students are discouraged from using their multimeters
to measure AC voltages around home or at school due to the lethal
shock hazards and the potential for severe burns from high currents.
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Digital Logic – Concept

Rather than referring to voltage levels of signals, we should consider
signals that are logically 1 or 0 (or asserted or de-asserted)
Truth
tables



Gates are simplest digital logic circuits, and they implement basic logic
operations (functions)
Gates are designed using transistors
Gates are used to build more complex circuits that implement more
complex logic functions.
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Digital Logic – Basic Laws of Boolean Algebra
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Operation AND: *
Operation OR: +
A
Inverse of A:
Identity Laws: A + 0 = A, A * 1 = A
Inverse laws: A+ A = 1, A * A = 0
Zero and one laws A + 1 = 1, A * 0 = 0
Commutative laws: A+B = B + A, A * B = B * A
Associative laws:


A*(B*C) = (A*B)*C
Distributive laws:


A+(B+C) = (A+B) + C;
A * (B+C) = (A*B) + (A *C); A + (B * C) = (A+B) * (A +C)
DeMorgan’s laws:
(A  B)  A * B
(A* B)  A  B
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Digital Logic – Minimization using Boolean Laws

Consider one of logic equations:
y1  x1 * x 2 * x 3  x1 * x 2 * x 3  x1 * x 2 * x 3  x1 * x 2 * x 3
 x1 * x 2 * ( x 3  x 3)  x 2 * x 3 * ( x1  x1)
 x1 * x 2  x 2 * x 3

But if we start grouping in some other way, we may not end up with the
minimal equation.
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Digital Logic – Venn Diagram



A Venn Diagram is a diagram that shows all possible logical relations
between a finite collection of sets.
It is conceived by John Venn in 1880.
It is used to teach elementary set theory, as well as illustrate simple set
relationships in probability, logic, statistics, linguistics and computer
sciences
A-Not
A and B
A or B
A xor B
Exclusive Or
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44
Lab 1 – Component Identification

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
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fixed & variable resistors including color codes
switches
relays
batteries including voltages
capacitors
diodes
inductors
transformers
photocells
transistors, integrated circuits & circuit boards
motors, electromagnets & fuses
vacuum tubes
speakers & microphones
45
Electrical Symbols
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46
Lab 2 – Mystery Component
Using your multimeter, determine all of the
electrical parameters of the mystery device
and diagram the device in the space below
showing resistance values and the connection
points of the various colored wires. Hint:
Symbol for a potentiometer (variable resistor)
is
Black White Red Gray White/Red Yellow Brown White/Green Extra Credit- 47K resistor -
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47
Lab 3 - DC Motors & Electromagnets

Measure and record the resistance of the motor. ________

Connect the electric motor to the 3 volt power source through the 25 ohm
potentiometer and connect you multimeter to measure the motor voltage. Observe
the direction of rotation of the motor and the relationship between motor speed and
the voltage applied.

Reverse the power leads to the motor and repeat the observations.

Measure and record the resistance of the electromagnet. ________

Connect the 6 volt power source to the electromagnet through the 25 ohm
potentiometer and connect the multimeter to measure the electromagnet voltage.
Observe how many washers the electromagnet will lift as a function of voltage
applied. Use the compass to determine the pole of the electromagnet.

Reverse the power leads to the electromagnet and repeat above.
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Lab 4 – Parallel /Series Resistance

Using the following labeled resistors:
4 - 68 ohm, 25 watt
2 - 830 ohm, 25 watt
1 - 1.6K ohm, 15 watt

Connect parallel / series combinations of the resistors to achieve the
labeled resistance values in the table below. When each value is achieved,
use the multimeter attached to record the Measured resistance.
Labeled
(ohms)
Measured
(ohms)
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34
68
136
272
415
551
619
830
1600
49
Lab 5 – Basic Digital Logic
A
B
0
0
0
1
1
0
1
1
C
D
0
0
0
1
1
0
1
1
E
INV
NOR
NAND
0
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F
G
0
0
0
1
1
0
1
1
OR
1
50