PART 1: MOVIES / INTRODUCTION / QUIZZES
(maybe do the demonstrations first)
I) nice introduction from brainpop
(also thunderstorm electricity )
II) watch
this video as an introduction ( 9th grade)
24 minutes - questions:
1) electricity is defined as the flow of _________________
2) the centre of an atom is called the ________________
3) objects that don't allow easily electrons to flow through them are called ___________
4) there are 2 kinds of electricity. static and _______ .
5) charges that are unlike will ____________.
6) what kind of charge does a proton have ?
7) what kind od charge does a neutron has?
8) What kind of charge does an electron have ?
9) name some things you shoud avoid if a lightning storm comes near. Are you safe in a car? why ?
(another
movie interesting for younger learner (8th grade) )
15 minutes
III) prepare the quiz. study and you will take the quiz in class.
IV) EXTRA CREDITS watch
this movie and answer the questions (30 minutes)
_______________________________________________________________________________
V) shart to keep in mind :
(it means if you rub rubber (ebonite) with fur (fair), the rubber becomes - and the hair + )
Hold electrons tightly
Sulfur
brass
copper
ebonite
wax
silk
lead
fur
wool
glass
hold electrons lightly
_________________________________________________--
V) FILL THE BLANKS - This will be part of our nexy quiz . :-)
1) Fill blanks:
An atom is made of the __________ in the center and a cloud of __________ around.
The nucleus is __________ charged and the electrons are ____________ charged.
The diameter of the nucleus of H is about 10-12 cm. or a millionth of a millionth of 1 cm. ( __________________ in standard notation)
It means you have to divide 1 cm in to 1 _____________________ parts to get the size of a nucleus.
The diameter of the whole atom (from center to cloud) is 10-8 cm. THis is ______ billionth of 1 centimeter. (1 billionth = 10-9)
It
means you need to divide 1 cm into 1__________________ parts to
vizualise the size of an atom. (not possible with the naked eye).
The atom is ______________ times greater than the nucleus. (find ratio 10-8/10-12). This is _____________ orders of magnitude.
(hint: 100 is 2 orders of magnitude )
If a nucleus were to be of a size of a marble (1cm), then the electrons would be at a distance of ___________ cm = _________ m
that is _________ meter sticks away. Or ________ miles away (1mile=1600m).
This is like one block away. (South-North in New York city)
2) Fill blanks:
remember rubbing glass +silk = makes the glass positive and the silk negative. (the silk takes the_________, it has more affinity for them)
rubbing ebonite (kind of plastic) + car fur = makes ebonite negative and the fur positive
(the ebonite takes the ________, it has more ________ for them)
A
conductor have a small amount of ___________ that are free to move
around, like a fluid can flow from a high position to a lower one.
This model of electrons, behaving like a fluid, was introduced by Benjamin Franklin who didn't know about electrons.
In
an insulator the electrons are attached to their atoms and are not free
to flow. However, if you rub insulators, they can lose electrons
(they
become _______ ________) or gain electrons (they become _________ __________) .
Although electrons can not flow in an insulator, they
can be taken away from an insulator or added to an insulator.
An
insulator can ________ electrons or __________ electrons. (it is called ________ separation).
3)
A)Like charges __________, unlike charges _________. When ebonite
is rubbed with wool, some ________ leave the _________
and move to the ________ so the ebonite becomes _______ charged and the wool is left __________ charged.
B) A negatively-charged object attracts a piece of paper because it _________ electrons away from the surface of the paper.
This leaves the surface of the paper ________ charged so that it is _______- to the object. These separated charges
are called po_________ charges.
C) In a gold-lead electroscope, the leaf rises because like charges _________
D) conductors (unlike _________ ) allow _________ to travel through them.
3) A)What is meant by saying charge is conserved ?
B) What part of an atom is negatively charged and what part of the atom is positively charged?
C) What kind of charges does an object acquire when electrons are stripped from it.
PART 2: DEMONSTRATIONS IN CLASS with the Van-Graaf generator + balloons
1) Fill blanks/ You need an aluminum helium balloon , glass rod, silk, cat fur, ebonite, regular balloon
Remember: the balloon is a conductor, its electrons are free to move on its surface.
Also, unlike charges ______________ and like charges ____________. The glass rod is not a conductor, it is a _______________.
Let's rub the glass rod. It is ________ charged. As you move it closer to the balloon (without touching it), the balloon
is
_________ to it. Explain why, using the fact that the balloon is a
conductor (electrons are free to move).
Imagine electrons being a fluid. Use the picture below.
On the balloon there is an equal number of ___________ charges and ____________ charges.
Explain what happens if we touch the balloon , several times, with the rod. (see below picture)
(remembers electrons can flow and they love positive charges)
The balloon becomes _____________ charged. (below) Explain.
Now
the balloon is positively charged. Let's now rub an ebonite rod with a cat
fur. The rod has more affinity for electrons than the fur
so
the rod becomes ___________ charged. What do you think will happen if
we get the rod close to our positively charged balloon?
(without touching it).
This kind of experiments showed Franklin that there are 2 kinds of charges.
Now in a conductor, electrons can't freely flow. They have to stay around their atoms, but they can move a tiny distance
such as the atom becomes polarized. Like a magnet has a North pole and a south pole, even if both poles are part of the same unit (atom or molecule)
Knowing that, can you predict what will happen if we now use a regular balloon (insulator) and
a negatively charged rod. The balloon is not charges, it is neutral and the electrons can;t move freely.
But the atoms can be polarized. Use the pictures below to explain the outcome.
inside the balloon:
Rub a neutral , regular balloon (insulator) against your hair. The balloon becomes charged
and will stick to a wall because the atoms in the wall, will become polarized. Try it.
2) more demonstrations
A dipole is a pair 2 charges, same magnitude but opposite charge. Much like a magnet has a North and a south pole.
We
are going to create a dipole (made of 2 conductive spheres) and try to
find out which one has the electrons (negatively charged) and which one
lost its electrons (positively charged). You need the ebonite rod +
fur, 2 spheres (ping pong covered by aluminum)
standing (stick a wood stick in it) on a non conductive bar, one electroscope.
The spheres are touching. They are not charged. Describe what happens when you bring a negatively charged rod next to them.
(rubbed with cat fur).. see below.
Now you separate the spheres, without touching them. you have an electric dipole. + -
you don't know yet which shpere is positive and which sphere is negative. You are going to find out using an electroscope.
Charge the electrocscope negatively. (touch it quickly with the ebonite rode rubbed with fur).
you should see its legs moving away from each other.
The electrons flow on the conductive legs and move away from each other as far as possible.
What do you think will happen if we bring the positively charged sphere close to electroscope ? what will happen to the reading
(will the legs move closer?) see below. What will happen if it is the positively charged sphere than you bring closer ?
This what you can tell which sphere is positivly charged and which one is negatively charged.
3) Demonstration with Van de GRaaf generator.
movie taken by a 9th grade student in class
This generator brings charges on the dome. It can be negatively charged or positively charged.
If you touch it and if you are wearing sneakers (insulator) and if you turn it on, you becomes charged and your hairs repel
each other. Charges love to accumulate in extremeties. Then you can charge your friends with your fingers,
you can make confeties dance on the dome, you can create nice sparks between the large dome and small conductive spheres.
then you can charge friends when they bring their finger close.
(videos to find)
4) demonstration you need Van de Graaf generator, aluminum helium balloon,
You can create a dipole between you and the van de Graaf generator.. Suppose you sit in front of it,
facing it. Suppose the de Graaf is positively charged. The electrons from the Earth will flow
through your body to face the positive dome. If you place a balloon between you and the generator and give it a push
so it touches the generator, it will become positive and will be repelled. It will touch you, will become negative
and will bounce back to the dome ... It will oscillate between you and the dome !
This is called an electric transfer.The balloon picks up (collects) charges from the generator and brings them
to the person. The charges can flow through the person into the ground. You can show the same phenomenon
with 2 cans of cafe and a thumbtack on a string between the cans (held by wood rod). One can has to be isolated from table
with a piece of wax. Charge one can with a large of plastic wrap rubbed with fur. (negatively charged).
The tack should oscillate between the 2 cans !
5) other thigs to try:
- place confettis on the Van-Graaf / place a paper wig
- charge a paper clip hanging on a string and let it oscillate between the Van-GRaaf and your hand.
- 2 charged paper clip hanging on a string will repell each other
- attract piece of paper with a rod
- build an electrocscope
THINK ABOUT THESE QUESTIONS
The Van graaf generator can produce 70,000 Volts ! why is it safe to touch it ?
The original Van graaf built in 1929 ? can be found in the Science Museum in Boston.
The giant generator can produce up to 150,000 volts ! Demonstrators show that it is
safe to stay in a Faraday cage.
6) exeriment to do : Kelvin's Thunderstorm : water-drop electrostatic generator
prodices 10,000 V
see here for a giant set upsee here for a simple set upsee here for more explanationsee this link for more
PART 3 - QUANTITY OF CHARGE, COULOMB's LAW - MORE MATH :-) get your TI
bring ping pong in class .
1) please read and
fill the blank:
The unit for charge is the Coulomb.
An elementary
charge, noted e, is equal, in magnitude (absolute value), to the charge of one
electron or one proton.
So one elementary charge = 1.6 10-19 C (or 1.6 E-19C in the TI)
The charge of a proton is + e = + 1.6 10-19 C, and the charge of an
electron is -e = - 1.6 10-19 C .
Is that number closer to millionth of millionth ? billionth of billionth ? trillionth of trillionth ?
______________________________
Neutrons are neutral. They don't have any charge. All atoms are
electrically neutral because they contain the same number of _________
and __________.
As seen previously, an object (an insulator like wool or
plastic) can be charged if it _________or loses _______ (by friction/rubbing for
example).
The net charge on a charged object is always an integral multiple of e.
\
That is charge on an object = an integer x 1.6 10-19C, you can have 2 e, -3e, 10e or -200 but you can't have 0.5e, 1.2e , -4/3 e .
You can't break " e" into smaller charges. So if the object can hold 2 electrons in excess, its charge will
be - 2 e
(that is charge = - 2 x 1.9 10-19C = __________ ). An The object (like hair) can lose 3 electrons so it will be charged positively . charge = 3 e = ___________C.
However, it can't hold half
of an electron, or a 5.6
electrons or 10.1 electrons. We say in Physics that charge is quantized.
Any charge stored in an object has to be an integral
multiple of _____ (3e, 5e, 1000e, - 100,000 e ....). OR Q = n e
Q is the total charge
, e is the elementary charge and n is the number of elementary charges
in Q. e= 1.6 10-19 C
The SI
of charge is the coulomb (C). One coulomb of charge (so Q = 1C ) is equal to
____________ elementary charges e (protons)
(hint: 1 proton has a charge of e = 1.6 10
-19 C and you are trying to find how many e can fit in Q = 1C. you can set a proportion
| number of e | charge in C |
| 1 | 1.6 10 -19C |
| X | 1C |
or you can use Q = n e and solve for n )
2) A) So if an object has a charge of 8 10-19 C, how many elementary
charges does it hold in excess ? _________________
(use: Q = n e
with Q = 8.0 E -19C) , e = 1.6 E -19C and
solve for n) or set a proportion as above:
| number of e | charge in C |
| 1 | 1.6 10 -19C |
| X | 8 10-19 C
|
Did it lose electrons or gain electrons ?
B) If the charge is - 1.6 10 - 18C , how many elementary charges now?
C) which particle has no charge? (neutron? electron? proton? quark ?)
3) A) A charge of 100 elementary charges is equivalent to
________________C (solve for Q, Q = ne)
B) A charge of 200,000 elementary charges is equivalent to
_______________ C
4) A strong lightning bolt transfers about 32C to EArth. How many
electrons are transferred ?
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