CIRCUIT LAB 1:– Pre-lab Questions
1. Which side of the LED is positive? Circle the correct answer: flat side, shorter wire OR round side, longer wire
2. Identify the following symbols used in circuit diagrams:
________________________
__________________________
_________________________
___________________
3. What colors, in order, are the bands on the 10K Ω resistor?
4. On the breadboard below, identify hole j3 with an arrow.
5. To which hole is j3 electrically connected ?
A. j4
B. f3
C. +3
D. -3
E. B,C,and D are correct
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EXPERIMENT #1: The LED
Parts Needed:
• a 9V battery or power supply
• one Switch
• one each of the following resistors:
• 10kΩresistor (marked brown-black-orange-gold, in that order)
• 1kΩresistor (marked brown-black-red-gold, in that order)
• 100kΩresistor (marked brown-black-yellow-gold, in that order)
• one LED
• 2 wires
Snap the battery into its clip. Make sure the r e d w i r e i s a t t a c h e d t o t h e p o s i t i v e t e r m i n a l a n d t h e b l a c k
w i r e a t t a c h e d t o t h e n e g a t i v e t e r m i n a l Always remove the battery from its clip when finished.
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Now insert the components for this circuit into your breadboard according to the Wiring Checklist below (the first
item is for the battery/power supply which you already did above). When you’re finished your wiring should look like the
diagram shown at right, with the exception of the
WIRING DIAGRAM
POWER
SUPPLY
RESISTOR
Wiring Checklist:
LED
(symbol shows flat
side is on right)
10k
(RED)
Insert red battery wire or positive power supply into
hole j4 and black battery wire or negative power
supply (ground) into hole (–)3.
Insert switch into holes f4 and f5.
Insert the 10kΩresistor into holes j5 and j9.
Insert the LED into holes g20 and g21. NOTE: The
“flat” side of the LED (as shown on the picture
above, and usually the shorter wire) goes into g21.
Insert a short wire between holes h9 and j20.
9V
BATTERY
Insert a short wire between holes f21 and (–)21.
(BLACK)
Be sure all your wires are securely in place and not
loose. Also make sure the metal into each hole is
not touching any other metal, including other parts
of the same component.
SWITCH
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WIRES
NOTE: The Wiring Checklist and Wiring Diagram show you ONE way of connecting the circuit components using
your breadboard. There are many other ways that are also correct. The important thing is that the electrical connections
are as shown in the circuit diagram (see below).
Press the switch and the LED lights up, and turns off when you release the switch. Well done! You’ve just built your first
electronic circuit!
Take a look at the water diagram (left, below) that follows. It shows the flow of water from the pump through the faucet,
the small pipe, the water meter, the large pipes, and back to the pump. Now compare it to the circuit diagram next to
it. Circuit diagrams, also called schematics, are the “maps” for electronic circuits. They show the flow of electricity from
the battery through the switch, the resistor, the LED, the wires, and back to the battery. They also use the symbols for
the battery, switch, resistor, and LED already shown.
Press the switch again and observe the brightness of the LED. Now remove the 10kΩresistor and replace it with a
1kΩresistor (marked brown-black- red-gold, in that order) in the same holes. Press the switch.
Q1. Does the LED get brighter, dimmer, or stay the same?____________________
Now replace the 1kΩresistor with the 100kΩresistor (marked brown-black-yellow-gold, in that order) and press the
switch again.
Q2. Does the LED get brighter, dimmer, or stay the same?____________________
Ohm’s Law: You just observed that when you have less resistance in the circuit, more current flows (making the LED
brighter). The relationship between voltage, current, and resistance is known as Ohm’s Law: I = V / R .
The units of current are Amperes (A), the units of voltage are Volts (V) and the units of resistance are Ohms (Ω).
Assume the battery voltage for the circuit to be 9.0 V and that the only resistance in the circuit is due to the resistor. What
is the value of the current in the circuit for each resistor you used in the experiment?
Q3a: R = 10kΩ, I = ________mA (milliamps or 1 x10-3 A)
Q3b: R = 1kΩ, I = ________mA
Q3c: R = 100kΩ, I = ________mA
Resistance: Resistance is the electrical “friction” between moving charges in a current and the material it is flowing
through. The result is that the kinetic energy of the moving charge is converted to heat. Resistors are made using
carbon and can be constructed with different resistive values, as shown in the preceding experiment. Incandescent light
bulbs use a small piece of a highly resistive material called tungsten. Enough current is passed through this tungsten to
heat it until it glows white hot, producing light. Metal wires have some electrical resistance, but it is very low (less than
1Ω per foot) and can be ignored in almost all circuits.
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In electronics we sometimes use a variable
resistor (see illustrations below). This is a normal
resistor (50k Ω) with an additional arm contact
that can move along the resistive material and
tap off the desired resistance. The dial on the
variable resistor moves the arm contact and
sets the resistance between the left and center
pins. The remaining resistance of the part is
between the center and right pins. For example,
when the dial is turned fully to the left, there is
minimal resistance between the left and center
pins (usually 0 Ω) and maximum resistance
between the center and right pins. The
resistance between the left and right pins will
always be the total resistance. Variable resistors like this one are used in the light dimmers and are also used to control the
volume o f radio, TV, and many electronic devices.
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EXPERIMENT #2: Brightness Control
Parts Needed:
• a 9V battery or power supply
• Switch
• one 1kΩresistor
• 50kΩvariable resistor
• one LED
• 2 wires
Wiring Checklist (
experiment):
) indicates same position as last
Insert red battery wire or positive power supply into hole j4
and black battery wire or negative power supply (ground) into
hole (–)3.
Insert switch into holes f4 and f5.
Insert the LED into holes g20 and g21 (“flat” side goes into g21).
Insert a short wire between holes f21 and (–)21.
Insert the 1kΩresistor into holes j5 and j15.
Insert the 50kΩvariable resistor into holes e14, g15, and e16. It
may be a tight fit, carefully press it in slowly.
Insert a short wire between holes c14 and j20.
Remove the 10kΩresistor used in Experiment #1; the other parts are used
here. Insert the new parts according to the Wiring Checklist below. Press the
switch and the LED lights up (it may be dim). Now hold the switch closed with one
hand and turn the dial on the variable resistor with the other. When the dial is
turned to the left, the resistance in the circuit is low. As you turn the dial to the right the resistance increases.
You may be wondering what the 1kΩresistor is doing in the circuit. If you set the dial on the variable resistor for minimum
resistance (0Ω) then Ohm’s Law tells us the current will be very large - and it might damage the LED. The 1kΩwas put
in to limit the current while having little effect on the brightness of the LED.
Remove the wire end from c14 and connect it to c16. Watch what happens when the dial is turned from left to right while
the switch is closed.
Q1: Explain what was different and why:
Q2: Remove the 1kΩresistor from hole j15 and insert it into hole c14 (the other end stays in j5). What do you think will
happen when you close the switch and turn the dial on the variable resistor?
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EXPERIMENT #3: RESISTORS IN SERIES
Parts Needed:
• a 9V battery or power supply
• Switch
• one 3.3k Ωresistor
• one 100k Ωresistor
• one LED
• 1 wire
WIRING DIAGRAM
POWER
SUPPLY
LED
+9V
0V
RESISTORS
Wiring Checklist ( indicates same position as
last experiment):
Insert red battery wire or positive power supply into
hole j4 and black battery wire or negative power
supply (ground) into hole (–)3.
Insert switch into holes f4 and f5.
Insert the LED into holes g20 and g21 (“flat” side
goes into g21).
Insert a short wire between holes f21 and (–)21.
Insert the 3.3k Ωresistor into holes i5 and i12.
Insert the 100kΩresistor into holes j12 and j20
(avoid touching other components).
100k
(RED)
3.3k
(symbol shows flat
side is on right)
9V
BATTERY
(BLACK)
SWITCH
WIRE
Q1: Draw the circuit diagram for the circuit in the
space provided. Note how the 2 resistors are
connected in series. The same current will flow
sequentially through each resistor.
Build the circuit according to the wiring diagram and
your circuit diagram and press the switch.
Q2: Observe the LED brightness. Calculate the
equivalent resistance of the circuit:
Press the switch one more time and observe the
LED brightness for comparison the next circuit.
EXPERIMENT #4: RESISTORS IN PARALLEL
In this experiment, you will build a circuit with the same components. The only difference is in how the 2 resistors are
connected. The 3.3k Ω resistor and the 100k Ω resistor are in parallel (connected between the same points in the
circuit). In the preceding experiment, the series combination of the two resistors was additive, it made less current flow
than either resistor by itself. In this experiment we will see how parallel wiring affects the current flow.
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Parts Needed:
• a 9V battery or power supply
• Switch
• one 1kΩresistor
• one 3.3kΩresistor
• one 10kΩresistor
• one 100kΩresistor
• one LED
• 2 wires
Wiring Checklist ( indicates same position as last
experiment):
Insert red battery wire or positive power supply (P. S.) into j4 and
black battery wire or negative power supply (ground) into (–)3.
Insert switch into f4 and f5.
Insert the LED into g20 and g21 (“flat” side goes into g21).
Insert a short wire between f21 and (–)21.
Insert the 3.3kΩresistor into i5 and i12.
Insert the 100kΩresistor into j5 and 12.
Insert a short wire between h12 and j20.
WIRING DIAGRAM
100K
Q1: Examine the circuit diagram. The current splits at the connection between the 2 resistors. Which do you think is
most likely?
A. The current flows equally through both resistors.
B. More current flows through the 100kΩ resisitor
C. More current flows through the 3.3kΩ or does more flow through one resistor than the other?
Q2: Explain your choice:
Q3: Compare the LED brightness (and therefore the amount of current in the circuit) with that of the series circuit in
Experiment 3. Is it brighter, dimmer or the same?
Q4: Calculate the equivalent resistance of the circuit (this formula can be found in your text or online). How does the
value that you calculated explain the behavior of the LED?
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EXPERIMENT #5: WATER DETECTOR
You’ve seen how current flows through copper wires easily and how carbon resistors resist the flow. In this experiment
you will test tap water, deionized water, and bottled water, and compare how well works to complete an
electrical circuit and light up the LED.
Wiring Checklist ( indicates same position as last experiment):
Insert red battery wire or positive P. S. into j4 and black battery wire
or negative P. S. (ground) into (–)3.
Insert an LED into g20 and g21 (“flat” side goes into g21).
Note: Keep the switch in the breadboard (unconnected) until later
experiments, as it can be difficult to remove and insert.
Insert the 470 Ωresistor into j12 and j20.
Insert the 1k Ωresistor into i4 and i12.
Insert the 3.3k Ωresistor into h20 and (–)18.
Insert the 10k Ωresistor into f20 and (–)21.
Insert a long wire into j21 (the other end is unconnected for now).
Insert a long wire into (–)25 (the other end is unconnected for now).
Parts Needed:
a 9V battery or power supply
small lab jack
one 470Ωresistor
one 1k Ω resistor
one 3.3kΩresistor
one 10kΩresistor
one LED
2 long wires
2 glasses of “unknown” water
Optional: glass of bottled water
TO GLASS
OF WATER
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Construct the circuit according to the wiring diagram and circuit diagram. Obtain 1 cup each of the unknown water types.
Dip the wires of the water detector in each one.
Q1. How can you tell which glass is the tap water and which is the de-ionized water? Why is this the case?
Fill another cup with bottled water if available. Be sure to rinse the cup with the bottled water first!
Q2: How does the bottled water compare with the other 2 types of water?
Q3: Calculate the equivalent resistance of the resistors:
a. Find the equivalent resistance of the 2 resistors in series: ________________________
b. Find the equivalent resistance of the 2 resistors in parallel________________________
c. Find the total equivalent resistance of all resistors in the circuit by assuming intermediate equivalents are in series with each other
(show your work below):
________________________ Ω
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