These slides include a presentation about the connections between math and electricity (Ohm's law, calculating voltage and resistance) as well as how-to slides so that you can make your own math quiz that lights a bulb to confirm when you have the correct answer. Note, the animations won't come through in this upload but for several slides I had the kids try to calculate the answers to my questions before I showed the answers.

1. Hands-on Science and
Engineering at Pasadena
Public Library
April 11, 2018

2. *Conductors and resistors
*The mathematical link between voltage and
resistance
*Building an electrical circuit

3. The Science of Electricity by Louise Spilsbury, pg. 10-11

4. The Science of Electricity by Louise Spilsbury, pg. 10-11
An open circuit
doesn’t allow
electrons to flow in
a loop from the
battery to the LED
and back to the
battery
A closed circuit
creates a loop
through which
electrons flow again
and again through
the LED, constantly
lighting it up

5. The Science of Electricity by Louise Spilsbury, pg. 10-11
A closed circuit
creates a loop
through which
electrons flow again
and again through
the LED, constantly
lighting it up
An open circuit
doesn’t allow
electrons to flow in
a loop from the
battery to the LED
and back to the
battery

7. The Science of Electricity by Louise Spilsbury, pg. 18

8. Eyewitness Electricity by Steve Parker, p. 22
Georg Ohm did a series of experiments
around 1825 demonstrating that there is no
such thing as a perfect conductor of
electricity. All substances put up resistance
to electrical current.
Ohm also found that long wires have more
resistance than short ones, and thin wires
have more resistance than fat ones.
Ohm discovered that, the more resistance
you have, the more volts you need to push
electric current through your wire.
Inversely, if you don’t have enough
resistance and too much voltage, your light
bulbs will blow a fuse!

9. https://magareyphysics.wikispaces.com/Resistance+%26+Ohm%27s+Law
Expressed as a
mathematical equation, this
means that the current (I) is
equal to the voltage (V)
divided by the resistance
(R), or:

10. • Red, yellow and white
LEDs typically use only
1.8V of energy to light
up. You shouldn’t use
too strong a battery—3V
is a good strength—
unless…
• You have a resistor!

11. Engineers use resistors to decrease or
divide up the voltage in a circuit. This is
important whenever you have different
electronic outputs needing different
voltages.

12. https://www.youtube.com/watch?v=NfcgA1axPLo
We will use resistors today so that our LED bulbs
(which work best with 1.8V of electricity) don’t
burn out when connected to a 9V battery.
(If you connect an LED to too much power…it
could explode!)

13. • Your LED will take about 1.8V of energy, so let’s calculate how many volts
will be left.
9V (power source) – 1.8V (voltage drop from LED) =
20mA = 0.02 amperes
7.2V
• We also need to know the current, expressed in amperes. For LED diodes
like ours, the maximum current they can handle is 20mA, the “I” that we
want to get when we add a resistor.
• How many Ohms do we need in a resistor to bring our current down
below the max current of 20mA?
1 Ohm is equal to 1 volt divided by 1 ampere: 1Ω = 1V / 1A
• How many amperes is 20mA, or 20 miliamperes?
(Hint: mili comes from Latin mille, or a thousandth)

14. Now let’s plug those numbers into our Ohm’s law
equation:
R = V / I
R = 7.2V / 0.02A
R = 360 Ω
Our resistor needs to be at least 360Ω.

15. We know we need at least 360Ω to get our voltage low enough for our LED.
We actually want less than 20mA of current—under the maximum amperage.
So it’s okay to use a resistor that is higher than 360Ω. Our resistors are
1000Ω.
How much current are we going to have with a 9V
battery and a 1000Ω resistor?
I = V / R
I = 7.2V / 1000 Ω
I = .0072A, or 7.2mA
7.2mA < 20mA

16. Make an electric
quiz that can test
your friends’ math
skills, using a
circuit that powers
a light bulb only
when they get the
correct answer!

18. The longer side is the “positive” side, and the
shorter side is the “negative” side. This is important
because in an electric circuit, electrons flow in only
one direction, from negative pole to positive pole.
(Incidentally, electric current itself is considered to
go in the opposite direction, from positive pole to
negative pole.)

19. 9V
1kΩ

20. 9V
1kΩ

21. http://dccircuit.wikispaces.com/01+Circuit+Symbols

22. Write questions and their
answers on post-it notes,
then line them up in two
columns on a sheet of
cardstock. Randomize the
order that the answers are
listed.
Poke a brass paper fastener
all the way through, next to
each question or answer
post-it.

23. Flip your cardstock over.
Wrap the cut segments of
copper wire to connect the
brass paper fasteners so that
questions will be connected
to their answers. Twist the
copper wire around the
fastener tightly so that you
will have a good electrical
connection.
Very Important:
Don’t let the wires touch
each other!

24. Attach the connector to the
top of your 9V battery. Then
adhere your 9V battery to
the front of your quiz using
tape. You can put tape on
the plastic coverings of your
wires so that they point in
different directions. Try to
point the red cable toward
the left side and the black
cable toward the right. This
will help you make sure your
wires never cross.

25. Find the positive (long) wire
of your LED, and twist one
wire of your resistor around
it tightly.

26. Make a loop with the other
wire of your resistor and
make another small loop with
the thin wires coming out of
the positive (red) cable of
your battery connector. Twist
them together tightly. Your
red cable should be pointing
toward the column of
questions on the left side of
your quiz.

27. Attach one of your silver
colored wires to the wires
on the black cable of your
battery connector, and
attach the other silver
wire to your negative
(shorter) wire of your
LED.

28. Keep your wires from touching
each other! You need them for
touching the brass fasteners!
You also need to keep the
connections taut. For my
sample, I had to weave my
“positive” wire around the
cardstock to keep it away from
the “negative” wire and
tighten the connections.
You could trim the wires if
needed. Your wires still need to
be long enough to touch all the
fasteners.

29. Press the wire connected to
your LED to one of the
“questions.” Press the wire
connected to your black
battery cable to one of the
“answers.” You may have to
press hard at first.
If it’s the correct answer, the
circuit should close, allowing
electrical current to pass
from one silver wire to the
other, by way of the copper
wires on the other side of
your quiz!

30. What if your LED won’t light up?
* The legs of your diode may need to be switched
around
* Jiggle or bend your quiz a little
* Make sure all the wire connections are tight
* Make sure no wires are touching that shouldn’t be
touching
What if your LED is lighting up when it’s not supposed
to?
* Make sure no wires are touching that shouldn’t be
touching

31. Electricity by Joseph Midthun and Samuel Hiti
The Science of Electricity by Louise Spilsbury
How Conductors Work by Victoria G. Christensen
A Project Guide to Electricity and Magnetism by
Colleen Kessler
Batteries, Bulbs and Wires by David Glover