Transcript PHYS111_26 - MrLaFazia.com

Conceptual Physics
TUESDAY November 23rd, 2010
LESSON GOALS:
• Discuss electrical background (think & share, and then general discussion)
• Go over important definitions and their applications
• include units for quantities (when applicable)
• Demonstrate 3 different ways to gain/give charge
• Demonstrate Van de graaff Generator use
• Take notes on Parallel and Series circuits
• Take notes on Ohm’s Law and Power calculations
• Complete Interactive Physics lab exploration on charged particles
• Take quick quiz on Ohm’s Law
• Recite Simply Shocking poem
http://mrlafazia.com/PHYS111/lessons/201011Fall/PHYS111_26.ppt
1/11
Discussion: Electricity
“What do you think of first when you hear the
word electricity? Describe a direct experience
you have had with electricity.”
(Share your thoughts with a fellow student).
Teacher-led Discussion:
• “Why do most people hire electricians”?
– what does “electricity” actually do to you...
• …on the small scale?
• …on the large scale?
2/11
Important Vocabulary to Discuss
(Part 1 of 2)
Charge (difficult to truly define) – consider it simply how “positive” or
“negative” (if not neutral) an object is. For us, this is considered to
be due to an imbalance of electrons and protons.
Unit of Charge?
Conductor, Semi-conductor, Insulator, and Super-Conductor
What are their characteristics, and when are they usually used?
Electric Field – discuss “positive test charge” (we will use this on our lab,
today) and draw out “electric field lines.”
Units?
Electric PE (and how does this relate to Voltage)?
3/11
3 Methods of “Charging”
Demonstrations on the following:
Charge by friction
Charge by conduction
Charge by induction (see “FIRST” note, below)
(FIRST, Consider “Coulomb’s Law” – don’t bother with the math, just
get the inverse-square relationship…will need to prove this
relationship in lab, today, as well).
(Define all of these, and know when they are occurring).
Danger: Many times they are used together, but they are certainly
happening at different times for the affected charges!
4/11
Important Vocabulary to Discuss
(Part 2 of 2)
Current
Unit of current?
Resistance
Unit of resistance?
Alternating and Direct Current (AC & DC, like the band)
What do graphs of these look like (Current vs. time)?
Where do we USE these different types of current?
Note: We can generate electricity based on the principle that electric
and magnetic fields are closely dependent on each other.
5/11
Van de graaff discussion and demo
How does the generator work?
Demonstrations:
Cup of Hanging Chads
a.k.a. the custodians hate me, now
Electric Field affect
a.k.a. Zeus’ lightning bolt
6/11
Circuitry: Series & Parallel
Ohm’s Law and Power calculation (as both equations and as triangles)
Simple sketch and rules for a series circuit.
Give example on finding resistance and then power.
Give example on finding current and then power.
Simple sketch and rules for a parallel circuit.
Give example on finding resistance and then power.
Give example on finding current and then power.
Where do we see these in our everyday lives?
7/11
Lab: Charges
Using the Interactive Physics program, create the following situations
and record your results: (Note that you may need to decrease charge
values if the results are too quick for you to notice!)
1)
2)
3)
4)
5)
A single positively charged object, anchored, with a “positive test charge” placed at
different points around it (draw the electric field for the anchored charge!)
A single negatively charged object, anchored, with a “positive test charge” placed at
different points around it (draw the electric field for the anchored charge!)
Two unanchored positively charged objects some distance apart.
Two unanchored (one positively and one negatively) charged objects some distance apart.
(Graph the velocity of one of the above objects (from #4) and show that the Force acting
on these charges probably does follow a non-linear pattern (as suggested by the inversesquare relationship with distance from Coulomb’s Law).
Experiment with your own charge configuration and record what happens!
8/11
Quiz: Ohm’s Law
“A 4 Ω resistor is in parallel with an 8 Ω resistor.
These are part of a circuit supplied with a
voltage of 12 V. What current is running
through the battery”?
9/11
Poem:
Simply Shocking, by D. LaFazia
Some of us learn the hard way.
Some choose to do the math.
Some people simply do not know,
Charge takes the easiest path.
When looking at the big picture,
You must know about the small.
Electrons are the reason,
That these circuits work at all.
Do not touch a live circuit,
If you know what's best for you.
Electricity will not be stopped,
By those simple tennis shoes.
Do not forget that people,
Are made of circuitry as well.
This is a lesson worth the learning,
'though it's not an easy sell.
When resistance is very high,
A car battery is tame,
But let a dipstick cross those leads,
And it will be YOU who deserves that name.
I hope that I have struck a nerve,
With all of these connections.
My series of words and parallel verbs,
I feel dispel perplexion.
No matter how a charge is gained
--whether friction or conduction or induced-If there is more or less charge than neutral,
SOMEthing is about to get "juiced".
If there is more you hope to know,
Be sure we have not made an end.
Electricity has more to tell,
And to the library I thee send.
I would not have you be afraid,
Of circuits (though I've not lied).
But be sure you're grounded when you work on
computers,
Or its components may get fried.
10/11
Looking Ahead:
• Next class (Tuesday, November 30th) we will cover
Selected Topic #2 (fluid dynamics!) This is the only truly
“math intensive” topic of the 3.
11/11