10-065 Van de Graaf Generator Instructions

Transcription

© Science First® 2005
Science First®
10-060/ 10-065 Van de Graaf
Generator Instructions
Instructions by: Dr. Zafar A. Ismail, Professor of Physics, Daemen College, Amherst, N.Y.
Caution:
People with cardiac
pacemakers should never
operate the generator or come
in contact with it. Discharge
of static electricity could
cause the pacemaker to be
damaged or to malfunction.
80-0161 Upper Comb Assembly
29-1016 Belt
80-0160 Upper
Pulley Assembly
80-0164
Column
Assembly
60-0601 Oblate
Introduction:
The Van de Graaf Generator
deposits a very large amount of
positive electrical charge on the
metal dome (oblate, globe). This
massive volume of positive electrical charge produces a spectacular display of lightning and other
phenomena.
When two insulators are
rubbed together, one loses electrons to the other and becomes
electrically positive. It has acquired positive electrical charges.
The other insulator, having gained
excess electrons (negative electrical charges) becomes electrically
negative. These charges are static
because they do not move on
their own. When you walk on a
carpet in a dry room with dry feet
you deposit a large amount of
electrical charge on your body;
the impact is felt when you touch
a door knob. Electrical charges
can also be induced on a neighboring insulator or conductor by a
process known as induction. In
the case of a flat insulator, the opposite side acquires opposite electrical charge by induction.
29-1070
Hose Clamp
26-2020
Motor
36-1062 Motor Mount
36-0605 Lower Pulley
Ground
Terminal
80-0163 Base
Use ground terminal to
attach 10-074 Discharge
Wand or other accessories
described in this booklet.
80-0161 Lower
Comb Assembly
The generator uses a plastic
(teflon) pulley at the lower end of
the machine, attached to an electric motor. A rubber belt passes
over the pulley. As the pulley
turns, rubbing occurs; the pulley
22-6025 Rubber
Feet
acquires negative charges while
the inside surface of the rubber
belt (in the vicinity of the plastic
pulley) acquires an equal amount
of positive charge. The outside
surface of the rubber belt acquires
95 Botsford Place, Buffalo, N.Y. 14216 U.S.A.
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Science First®
Schematic shows positive charges
carried upward from teflon pulley to
collector sphere
an equal amount of negative
charge by induction. An electrode,
in the form of a comb or brush, is
provided to drain away these
negative charges from the outside
surface of the rubber belt to the
"ground."
A similar comb (electrode) is
provided at the upper end where it
will provider a path for positive
charges to be taken to the collector dome. The plastic pulley retains the negative charges that it
acquired.
Positive charges stay on the
inside surface of the belt and
travel upwards as the belt moves
up. At the top, it runs over a me-
Start-Up
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tallic pulley (aluminum) which
picks up these positive charges
and retains them. Free electrons
from the metallic pulley flow on
the electron-deficient belt and are
carried down to the plastic pulley.
As the belt keeps running, more
charges are deposited on both
pulleys, resulting in heavy
buildup of charges on each. Soon
this buildup reaches ionization
intensity in the vicinity of the two
comb assemblies and a large number of positive and negative
charges are generated. The positive charges are transferred to the
collector dome by the upper comb
and the negative charges are
drained to the ground by the
lower comb. The belt plays an
important role in transporting
negative charges from upper to
lower comb and positive charges
(on other half of the belt) from
lower to upper comb.
Once on the metallic collector
dome, the positive charges spread
out due to electrostatic repulsion
and become uniformly distributed
because of the dome's spherical
shape. The buildup of positive
charge on the dome continues until ionization intensity is reached.
This is the equilibrium state and
limits the quantity of charge that
the generator can place on its
dome. It is measured in volts.
Combs reach
ionization intensity
Once this limit is reached
(200,000 potential for 10-060,
10-065, 10-061 and 10-066),
the air between dome and lower
housing gets ionized and a discharge with spark. The discharge
causes the potential to fall below
the ionization intensity but is
brought up to the limit again in
seconds, and another similar discharge occurs. The process continues as long as the generator is
running.
Teaching with Van de Graafs
Concepts: Frictional charge
generation. Electrostatic
repulsion (& attraction.)
Charging, discharging.
Discharge through sparks.
Plasma. Lightning.
Curriculum Fit: Grades 6 - 8, PS/
Electricity and Magnetism.
Units: Static Charge. Also,
Moving Charge & Magnets.
Concepts: Electrostatic Fields,
electric potential. Coulombs
Law demonstration.
Curriculum Fit: Grades 9-12, PS/
Electricity and Magnetism.
Unit: Static Charge.
Stand on plastic
stool to raise hair.
Dome reaches ionization
intensity
Science First®
Demonstrations:
(1) Hair Raising:
Approaching a running generator can be a hair raising experience. This is because the charges
are transferred to your body and specifically - to the hair. Due to
electrostatic repulsion between
similar charges, every hair tends to
get as far away from every other
hair as possible. This raises hair
and can be felt on head, arms and
all over the body.
For best results you need two
people and a plastic footstool.
Stand on the footstool and place
one hand palm down on the globe
of the Van de Graaf before your
helper turns on the generator.
Keep your hand on the globe, with
your other hand at your side taking
care not to touch anything else, the
entire time the machine is running.
Shake your hair lightly to loosen
the strands; wait 1 - 2 minutes.
You should now feel each individual strand start to lift. Have
your helper angle a mirror (taking
care not to get too close to you!)
so you can see the results. Fine,
light, long hair works best. Make
sure you do not remove your hand
from the globe, touch anyone or
step down from the footstool
while the machine is running. If
you do, you will feel a mild shock.
This is because, by doing so, you
have completed the electrical connection and grounded yourself.
(The footstool serves as an insulator.) The static electricity, instead
of remaining on your body, passes
to earth. You feel the results.
This experiment works best on
days when humidity is low. Water
vapor drains static charge. If you
do demonstrate on high-humidity
days, dry the inside of column and
globe with a hair dryer immediately before experimenting.
To raise hair, stand on footstool or
other plastic (nonconducting)
platform to insulate yourself.
(2) Electric Wind:
Charge distribution on the collector dome is isotropic because
the dome is predominantly spherical in shape. The distribution will
not be isotropic for irregularly or
asymmetrically shaped objects.
This is because narrower parts
always carry much greater concentration of charges than broader
parts. The effect would be maximum for pointed objects like thin
rods or large needles.
Try attaching a conductor in
the form of a sturdy, light, thin
metallic rod six to eight inches
long (for instance, a darning
needle) on the body of the collector dome, radially outwards. Use
tape or clay to attach. The concentration of charges at the tip of the
needle will be so intense that it
will ionize air in its neighborhood.
Negative ions will rush towards
the collector dome and neutralize
their charges. Positive ions, however, move away (due to electrostatic repulsion) from the generator and do not get neutralized. As
the generator is continuously running, it keeps supplying more and
more positive ions at a fast speed.
The ions running away form a
wind called electric wind which
blows away (radially outward)
from the generator. By attaching
the conductor or needle, you have
created an electric wind.
Generate Statics.
The wind is strong enough for
its effects to be experienced as far
away as 10 feet from the generator. It may not deflect a flame that
far away but will certainly impart
statics to your clothing which
would cling to your body; or to a
paper that would cling to your
hand or to the wall.
Turn a vane.
Place a vane, such as a childs
pinwheel, in front of the conductor. It will turn in the direction of
the wind. See for yourself what
the wind direction is and see if
you can form some idea of how
strong the wind is. Try a vane
that is slightly stiff and requires a
stronger wind to turn it.
Spin a spinner.
Make a small spinner using
aluminum foil 1" across with 4 - 6
blades. Use a sharp pin to act as
axis for spinner and mount the pin
on a wooden or plastic stick. Try
placing 2 beads on each side to
localize the spinner. When
brought near the conductor, the
electric wind will spin it.
Deflect a Flame.
Bring a lighted candle near the
conductor. The flame is deflected
away from the generator in the
same manner as an air draft.
Rotate the collector dome.
Show how an actual (electric)
wind can be created by ionized air
molecules running away from the
pointed conductor.
The ionized molecules move
away from the sharp or rounded
end of the conductor in great
numbers and at great speeds.
This, according to Bernoulli's
Principle, produces a low-pres-
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sure region in front of the tip of
the conductor. The rear end of the
conductor (attached to the dome)
remains at normal pressure. This
sets up a pressure differencenear
the conductor. By using it, you
can rotate the dome.
Attach two identical sharp or
rounded conductors tangentially
(not radially) to the collector
dome at its equator (along the
seam) on opposite sides and in
opposite directions. Conductors
can be attached with clay or tape.
Observe how pressure differences
in the vicinity of these conductors
exert torques on the collector
dome which begin to rotate
slowly but steadily. The dome
continues to rotate as long as the
generator is running. The mass of
the dome is in excess of 200
grams excluding masses of the
conductors. The fact, therefore,
that the dome will rotate solely
due to the electric wind that is
generated is a testimony to the
strength of that electric wind.
Electric Wind. Conductor is needle
attached with clay.
Science First®
needles eye. Attach the other end
of the wire to the collector dome
with transparent tape. Carry the
needle as far as the wire will allow you to carry it. Place it near a
candle and watch the electric
wind (emanating from the
needles tip) deflect the flame or
turn a vane or rotate a spinner.
(3) Lightning:
Lightning, an awesome natural
phenomenon, is an electrical discharge between clouds and the
ground. Create it in miniature
with a Van de Graaf Generator
due to the buildup of positive
electrical charges on the dome.
Bring a rounded object (metallic, for best results, such as a mixing bowl or juice can or 10-074
Discharge Wand) near the dome.
You may wish to wear a glove or
use a dry towel to hold the objects
as you approach the dome to
minimize the likelihood of receiving a shock. The discharge that
occurs between rounded object
and collector dome is accompanied by a crackling sound and can
be made brighter and more frequent by bringing the rounded object closer (from 2" to 1/2" away.)
If you withdraw the rounded object, the discharges become feeble
and less frequent and may be seen
only in a darkened room.
You should hear intermittent
crackling sounds and see feeble
sparks in darkness.
(4) St. Elmos Fire:
Carry the Electric Wind.
In this experiment you bring
the wind to the candle instead of
bringing the candle to the generator to observe its effect on the
flame. Prepare a large darning
needle by securely attaching a
well-insulated copper wire in the
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Electrical discharges from
clouds to the earth are of three
different types.
Point Discharge.
There is no visible light or
sound. Point discharges are responsible for the bulk of discharge between clouds and
ground.
Corona Discharge.
It is accompanied by visible
light but no audible sound. This is
known as St. Elmos Fire.
Lightning Discharge.
This is accompanied by blinding light and deafening sound.
You can create St. Elmos Fire
in a dark room by installing a
sewing needle perpendicular to
the dome using a drinking straw
or small plastic strip. Tape the
needle to one end of the straw,
hold the straw by the other end
and press it lightly against the
dome. (The object, of course, is
not to obtain a shock as you approach the dome with your hand.)
A small but significant glow or
fire appears at the tip of the
needle.
St. Elmos Fire can also be created by attaching a 3' long electrical wire (not solid, but stranded)
to the eye of a sewing needle. As
the strands are passed across the
eye, fold and twist them with pliers to join the needle solidly to
the wires end. Connect the other
end of this wire to the ground
connector on the base of your Van
de Graaf. (This procedure will not
work if your receptacle has only
two flat holes.) Now tie the needle
perpendicularly to one end of a
drinking straw using cord or tape.
Hold the far end of the straw and
bring the needle close to the dome
to watch the fire glow.
With this method, you can
study the effect of distance on the
glow. The glow will be stronger in
the vicinity of the dome. As distance increases, the glow dims.
Determine the firing distance - the distance over which
the glow is visible.
(5) Lighting:
You can light a variety of light
emitting devices with your Van de
Graaf - incandescent (filament)
light bulbs, fluorescent tubes or
lamps, gas filled tubes, old radio
tubes, even tiny neon tubes. For
best results, do these experiments
in a darkened room or at night.
Bring your bulb toward the
dome as the generator is operating. You may wish to make a nonconducting holder for the light
bulb to avoid receiving a shock as
you approach the dome. The outside glass surface nearest the
dome acquires negative charge by
induction. The charge builds up
on the glass surface to discharge
intensity. As discharge occurs,
negative charges rush through the
entire bulb, lighting it up for the
duration of the discharge.
Experiment with distances between bulb and dome. The bulb
will light even when 12' away
from the dome. Here, discharges
will be stronger but the intervals
between them will be longer. The
light bulb will also glow more
brightly. When you bring the bulb
nearer, the discharges are more
frequent but the light is dimmer.
the bulb touches the dome, the
light may be continuous (or flickering) but the intensity is low.
Household (incandescent)
bulbs will glow with purple light.
Other gas-filled tubes will glow
with the characteristic lights of
the respective gases.
Science First®
More
Demonstrations:
These experments require a few simple
devices made from common materials.
(1) Test Probe
This can be made out of a
spherical metal object, about 1" in
diameter, threaded, such as for a
cabinet. Drill a hole in a ruler near
one end for a screw. Take a piece
of well-insulated copper connecting wire, 2-3' long, bare one end
and fold it around the screw
loosely. Fix the knob on the ruler
with the wire attached to the
probe in between two washers,
using a solderless crimp terminal.
Bare the other end of the wire and
ground it by connecting it to the
ground connection on the base.
Eye of needle
Insulated
copper wire
Washers, 2
knob
Screw
Darning
needle
Straw
Movable Electrode
ruler
Copper wire
Test Probe
(2) Neon Bulb Probe
Mount a small neon bulb (i.e.
Ne2) on a plastic ruler. Turn the
two lead wires at right angles,
with one protruding from the ruler
by 1". Solder an insulated copper
wire to the other end and ground
it by connecting it to the ground
connection on the generator base.
Lead
wire
Fluorescent bulb
approaching collector
dome glows more brightly
(3) Movable Electrode
Take a piece of well-insulated
stranded copper connecting wire
about 3' long. Bare a length 1" on
each side. Pass the strands at one
end through the eye of a darning
needle about 6" long. Twist the
wire using a pair of nose pliers
until the needle is solidly connected to the wire. Solder the copper parts (optional). Attach the
needle to a plastic rod such as a
drinking straw by passing the
needle right through the straw
near one end. Or, use a 6" plastic
or wooden ruler, attaching the
needle with cord or tape. Do not
ground this wire.
Bulb
secured
by tape
Neon bulb
Lead wire
soldered to
copper
Plastic ruler
Neon Bulb Probe
(4) Cylindrical Box
Roll a piece of clear, strong
plastic sheet into a cylinder or
tube about 6" tall and attach 2
metal caps (such as lids of mar or
peanut butter jars) to the ends.
Glue one cap to the tube but do
not glue the other.
Use this box to carry foam
pieces painted with conductive
paint. Connect the upper and
lower electrodes to the generator.
Clear
plastic
cylinder
body
Cylindrical Box
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Experiments:
1. To determine the effective
spark distance of the
generator
For best results, do in a dark room.
When the grounded spherical
test probe is brought near the
dome, lightning discharges occur,
accompanied by a crackling
sound. You can enhance the effect
by bringing the probe close to the
dome. As it is moved farther
away, the intensity of light and
sound will diminish. To find the
maximum effective distance at
which visible light and audible
sound occurs, move the probe
back systematically until lightning
can just barely be noticed. This is
the effective spark distance of the
generator. Repeat in different directions. -Expect equal effective
distances on all sides. Look for
any deviations.
2. To study the electric field
intensity around the
collector dome.
The grounded neon bulb draws
energy from an electrostatic field
such as the field around the collector dome. If this energy is sufficient to excite the bulb, the bulb
will flow.
Bring the bulb probe close to
the dome (without touching it
with the exposed terminal of the
probe) and find the location where
it just barely lights up. Study the
extent of the field by moving the
bulb in all directions. You should
expect the field to be symmetrical
but you might wish to look for abnormalities or defects where the
intensity diminishes.
6
Science First®
3. To set up jumping balls in
a box.
Cut some small foam circles
from foam packing material and
cover them with electrically conductive material such as soot or
graphite (from soft pencils). Or
rub them against carbon paper.
Place conductive balls in the
cylindrical box (described earlier). Connect the upper and lower
electrodes (caps) of the box to the
DOME and GROUND respectively, using well insulated copper
connecting wires. The two caps
will become electrically charged.
Observe that at first the balls
will be on the lower cap. Here
they become charged negatively
and are repelled away toward the
upper cap. The upper cap becomes positively charged and attracts the balls.
The balls continue to move upward until they hit the upper cap.
On impact, their negative charge
is neutralized and they become
positively charged instead.
The balls now fall down to the
lower cap where the balls will
once again acquire a negative
charge. The up and down motion
continues as long as the generator
is running.
against a buildup of charge. Use a
tongs to bring the flask in contact
with the dome. A greenish-pink
glow should develop inside. This
is a replica aurora borealis.
5. Demonstrate electrostatic
repulsion
Use metal streamers such as
Christmas tinsel or graphitecoated pith balls* placed in a
bundle with one end tied together.
Attach the tied end to the dome
with tape and start your generator.
All strands will be charged positively and will stand erect, moving as far away from one another
as possible. The effect is similar
to HAIR RAISING and is a direct
result of electrostatic repulsion.
You get the same effect if you
use long, thin strands of paper
coated with graphite from a soft
lead pencil. Tape to the dome;
start the generator; watch the
strips repel each other.
4. Create miniature aurora
borealis
You Need: Pyrex flask
Fill a pyrex flask 1/3 full with
water and heat until the water
boils. When the flask is filled
with steam, remove from your
heater or burner and immediately
cork. Allow to cool. As the steam
settles and changes to water, a
partial vacuum is created. It will
be saturated with fine water vapor
but there will be no air inside the
flask. Do not handle the flask directly, even with gloves or plastic
as you will not be protected
Electrostatic
Repulsion
6. Electrostatic spray
painting.
You need: food coloring, spray atomizer
The electrostatic field of the
generator can be used to direct the
fine mist of paint as it comes out
of a sprayer nozzle. The particles
in the mist are charged electrically
which causes them to remain
within the electrostatic field. This
reduces the loss of paint due to
random scatter. The use of this
technique in commercial spray
painting requires only half the
paint otherwise needed.
To test this feature of the electrostatic field, use a perfume atomizer. Fill an empty atomizer
bottle with water colored with
food coloring. Spray the colored
water from the atomizer in the vicinity of the collector dome, tangentially across (not radially toward) the dome.
Notice how the spray gets
trapped in the electrostatic field
and bends toward the collector
dome. The spray is localized and
there is little waste.
Safety, Operation
and Maintenance:
Safety:
This generator is safe when used
properly. As with all electrical
appliances, follow these general
safety rules.
1. Plug the generator into a
grounded (3-prong) 110 volt
60 Hz outlet only. (10-061,
10-066 use 220 v 50/60 Hz.)
2. Do not operate in a wet or
damp location or outdoors (to
avoid shock).
3. Check for loose, worn or
frayed wires. Replace any defective parts. (See parts list).
4. Since discharge of electricity
can damage electronic devices,
keep away from appliances
such as televisions, computers,
stereos, microwave ovens.
5. The shock caused by touching
the generator directly is not
harmful and is similar to the
Science First®
shock received when walking
across a carpet and touching a
metallic object. It may feel uncomfortable however and
should therefore be avoided.
6. Adult supervision required.
Getting the Right Output:
Output is determined by the
number of popping sounds you
can hear in a timed interval or by
estimating the length of spark.
10-060, 10-065 and 10-066
should pop once a second.
The size of the globe determines voltage. The voltage determines the spark length. The
200,000 volt generator should
produce a spark length up to 8"
(5" is typical).
The shape of the globe needs
to be smooth and round. Any
burrs or sharp points will cause
loss of charge. Dents will not materially affect performance as long
as dents are smooth and shallow
with no rough edges.
Operation:
Best results are obtained in
low humidity. High humidity
causes charges to dissipate, lowering the electrostatic field, as water
vapor in the air drains your
charge. High humidity also causes
gradual deterioration of the belt.
We recommend that you operate your generator at humidity
levels of 75% or less. Your machine will run, however, at humidity levels up to 90%. At humidities in excess of 90%, the life of
the belt will be shortened drastically even though the machine
may function normally. The belt
may show signs of breakdown after 20 operating hours.
Your belt contains a special
ozone retarding formula which
should give you hundreds of
hours of operating use under lowhumidity conditions. The tension
of the belt, however, is crucial.
Belt tension is high when it leaves
our factory but may loosen with
use. If your belt is too tight when
you first receive your machine (or
have first assembled it in kit
form), you may loosen it by
stretching TWICE to twice its
normal length for a period of several seconds, then releasing. Do
not stretch further than the width
of your outstretched arms.
Stretching too far may break the
belt. By following this procedure,
you should have relaxed the belt
to its proper tension.
Common Operating
Problems:
a. Unsatisfactory Performance:
Low Current Yield
If your generator produces
weaker than normal current, it
will result in weak lightning discharges at shorter than normal distances. This is caused primarily
by a damp or dirty belt. Wash the
belt with soap and then rinse thoroughly. Check, also, for too much
clearance between belt and upper
and lower combs. Combs can be
adjusted manually by bending
them toward the belt for better
contact and should be within 1/8"
(3 mm) of the belt, but not touching it. If your comb is too short,
order replacements from us.
Another common cause of initial poor performance is high humidity. Dry the inside of the column and globe with a hair dryer
before using. This removes humidity inside the machine. You
may also run the generator for
several minutes before raising
hair. This creates enough heat to
eliminate effects of humidity.
7
b. Unsatisfactory Performance:
Low Voltage Yield
If your generator produces a
weaker than normal electrostatic
field, it will result in less intense
discharges. You may also see localized tiny flashes on the collector dome. This is due to a buildup
of dust or lint on the collector
dome itself or on the glued joint
of the two halves of the dome.
Such buildup should be cleaned
with a damp cloth. The housing
that covers the motor and plastic
pulley should be cleaned as well.
Storage:
To store for a long time, remove the belt to relax its tension
so it will not lose its original
strength. Store in a dry place.
Maintenance:
Bearings: Apply a drop of
lubricating oil once a year to
upper pulley bearings.
Belt: After every 50 opperating
hours, apply soap and scrub to
remove any deposits of
conducting material that may
accumulate on the belt. Rinse
thoroughly to remove soap.
Pulleys: Clean upper (metal)
pulley with rough cloth, sand
paper or steel wool and wipe
off any deposits caused by
wear and tear. Clean the lower
(teflon) pulley with a soft
cloth. Clean both pulleys
occasionally with alcohol,
especially if you are having
operating problems.
Science First®
Warranty and Parts:
We replace all defective or
missing parts free of charge. Additional replacement parts may be
ordered by referring to part numbers as illustrated. All products
warranted to be free from defect
for 90 days. Does not apply to accident, misuse, or normal wear
and tear. Made in U.S.A.
Van de Graaf
Accessories
These accessories may be purchased from most science education distributors or from manufacturer Science First®.
10-074 Discharge Wand
Discharge your machine at a
comfortable distance. Draw long
arcs during experimentation. Contains 7" diameter aluminum globe
mounted on PVC column and attached to a cast tripod base. Stand
discharge wand next to Van de
Graaf and watch the sparks fly.
Includes ground terminal which
can be clipped to ground terminal
to terminal on base of 10-060.
Pith Balls
29-1046 - 3/8" diameter balls
with thread. Pack 6 .
29-1073 - Graphite-coated
pith balls with attached thread,
Pack 6.
For experiments in electrostatic
repulsion.
10-615 Volta's Hailstorm
Tiny polystyrene balls, included, bounce wildly inside our
transparent chamber when near a
Van de Graaf generator. Instructions include theory. 12" high, can
be seen from a distance. Good
value.
8
10-070 Footswitch
Start and stop your machine
with a press of your foot. No danger of shocks since you don't get
too close; a useful accessory for
hair-raising. 110 volt only.
10-072 Footstool
The best way to perform the
hair-raising experiment is to stand
on our plastic footstool and place
your hand on the globe before
starting the Van de Graaf. Because
you're insulated from the ground,
your hair will start to rise as each
strand develops a positive charge.
10-055 Mylar Foil - 6 strands
For experiments in electrostatic repulsion. Tape to dome.
10-620 Static Spinner
Detect an invisible electric
wind. Pinwheel type spinner will
rotate when near a Van de Graaf
Generator. Good value.
10-610 Lightning Leaper
Show that electricity will follow the path of least resistance.
Watch sparks jump the gaps on
our insulating plate. Good value.
Replacement Parts:
Please call for prices.
24-1060
80-0169
29-1016
29-1070
36-1062
36-0605
60-0601
80-0160
80-0161
80-0162
80-0164
56-0605
56-6060
80-0163
80-0166
80-0167
50-0609
51-1002
56-1016
26-9016
51-1004
26-1005
22-6025
26-2018
80-0168
22-6033
Instructions
Motor, 110 v with pulley
Belt (3/4" wide)
Hose Clamp
Motor Mount
Lower Pulley (Teflon)
Globe (Oblate) (7")
Upper Pulley Assembly
Upper Comb Assembly
Lower Comb Assembly
Column Assembly
Column Only
Molded Ring
Base
Cord Set
Housing
Upper Pulley
Shaft
Shaft Collar, pair
Copper Wire
Collector Support
Lower Comb Terminal
Rubber Feet
Motor, 220 v
Cord Set, Europe
Strain Relief
Science First®
10-060/10-065
Parts
10-065
Kit Assembly:
Tools Required:
36-1062 Motor Mount
80-0169 Motor, 110 v with pulley
80-0164 Column
Assembly
Assembly should take 30-60 minutes
and can be done by ages 12 and up
with adult supervision.
Parts List
29-1070 Hose Clamp
22-6033 Strain Relief
36-0605 Lower Pulley (Teflon)
80-0160 Upper Pulley Assembly
Screwdriver
Pliers
Scissors or cutting pliers
11/32 wrench (optional)
80-0167 Plastic Housing
80-0162 Lower Comb Assembly
29-1016 Belt
Quantity
20-1202
Screws 6-32 x 3/8
20-1307
Screws 8-32 x 1/2
20-1324
Selftap 8-32 x 1/4
20-2306
Hexnuts 8-32
20-3202
Flatwasher #8
20-3331
Lockwasher #8
21-1310
Screw 8-32 x 1
21-2318
Knurl nut 8-32
22-6025
Mushroom feet
26-1000
Wire nut, gray
26-1005
Solderless terminal
80-0166
Cord set, 110 v
26-2020
Motor, 110 volt
26-9016
Copper wire #16
29-1016
Belt, neoprene
29-1070
Hose clamp
80-0160
Upper pulley assembly
80-0161
Upper brush assembly
Packed in bag with instructions.
80-0162
Lower brush assembly
80-0163
Molded base with/ holes
30-0162
Molded motor mount
80-0167
Housing with notches
56-0605
Lower teflon pulley
60-0601
Collector globe, 7"
24-0160
Instructions
22-6033
Strain relief
22-6033
Nut
220 volt version substitutes:
26-2018
220 volt motor
80-0168
Cord set, European
2
2
3
5
1
2
1
3
2
3
1
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Make sure all bare wires
are covered when
assembling this unit!
1. Rubber feet to base.
80-0161 Upper Comb Assembly
60-0601 Oblate
Turn base upside down to expose
bottom where label is attached. Twist
the 3 rubber feet into 3 molded holes
in base. Rubber feet will fit snugly.
Twist by hand as you would a screw.
9
Science First®
5. Connect wires.
Diagram 3
Diagram 1
D
2. Attach cord to base.
Turn the base right side up.
Take the end of cord with 3 exposed wires (end without plug) - two
are bare wires extending beyond
black and white plastic insulation, and
one is green. Push about 4" of the
end through 3/8" hole in rim of base
(Hole A in Diagram 2). This is largest
hole in rim of base. (Model 10-066
has yellow-green insulation connected
to ring terminal. The bare wires have
blue and brown insulation.)
Diagram 2
Hole A
Strain relief
Place 22-6033 strain relief over
wire. The stain relief is a black plastic
part which installs from the outside of
the base. Run threaded sectin through
Hole A. Tighten 22-6034 nut on
from inside.
3. Install motor mount.
With base right side up, press motor mount, circle side down, into
molded circular indentation in center
of base. Do this by lining up two
holes in base (D, E) with two notches
in base of motor mount.
The motor mount has been specially molded to fit in one way only,
since one edge has slight flattening in
an otherwise smooth curve. If mount
does not fit flush with base, rotate it
180°. Line up holes and notches until
fit is smooth.
10
E
Insert 2 short screws, 8-32 x 1/2"
(#20-1307) downward through both
motor mount and base. Turn base
over so label shows. Attach one
lockwasher (#20-3331 with slit) and
one hex nut to threaded end of each
protruding screw. Tighten with screwdriver to hold motor mount in place.
4. Install motor.
Turn the base right side up. To
attach motor to motor mount, hold the
motor with the wire coil to your right,
as shown in Diagram 4. Note the
teflon pulley is preinstalled on the
motor's central shaft. Press two (2)
threaded studs through the two (2)
holes at the rear of the motor mount.
Grasp the green wire of the cord
set, and feed the wire through the
large oval opening the back of the
motor mount. Next, using the pliers,
attach the ring terminal to the green
cord. Press the terminal ring at end of
the green cord onto top stud of motor.
Fasten in place with lockwasher (Part
20-3331) and hex nut.
Use a screwdriver to bend the
metal base of terminal ring away from
motor shaft and pulley. The ring
should bend backwards about 90°
away in the center of opening.
Make sure the terminal ring does
not touch pulley or any part of motor.
Otherwise the pulley will bind.
Diagram 4
#1
#2
Connect one wire with bare end
from cord set to one of wires from
motor (does not matter which). Twist
free (exposed) ends of cord set wire
and motor wire together. Stuff combined ends inside one wire nut
(#26-1000), a gray triangular plastic
piece, and twist wire nuts to tighten.
Do not leave any bare wire exposed
as this is a safety hazard and will affect performance. Repeat for other
pair of wires, using second wire nut.
6. Install lower brush.
The lower brush assembly (part
number 80-0162) consists of a plastic casing with terminals at either end.
One end contains the copper brush
approximately 1" long. Bend the copper brush away from terminal and
attach the terminal to the bottom stud
(see Diagram 5) of the motor. Follow
with the lockwasher and hex nut.
Tighten. Adjust the position of lower
brush so it comes within 1/8" of belt
but does not touch.
Diagram 5
7. Fasten brush assembly.
Place a knurl nut (#21-2318), hex
nut and flatwasher (#20-3202, with
slit) in that order on longest screw,
sized 8-32 x 1" (#21-1310). From
outside, with threaded stud pointing
inward toward center of base, twist
the screw into the hole in the rim of
base. This hole is to the right of the
motor mount near the lower edge of
rim, larger and lower than the hole
which is located even farther to the
right.
From inside, attach terminal on
free end of lower brush assembly to
exposed end of screw.
Science First®
Diagram 6
Refer to Diagram 6. Use second
hex nut, referred to as inside hex nut,
to attach terminal of lower brush.
This procedure is complex because
the base has been molded to fit as
tightly as possible.
Hold protruding end of screw
flush against inside hex nut as shown.
Support inside hex nut with your finger to keep it in place. Use 11/32
wrench or pliers in your other hand
to tighten outside hex nut. When fully
tightened, screw, lockwasher, outside
hex nut and knurl nut will protrude
about 3/4" beyond rim of base on outside. The knurl nut should be able to
move freely between outside hex nut
and screw head.
This creates a discharge terminal
for lighting and other experiments.
8. Install column.
Diagram 7
Use the hose clamp
(#29-1040), a metal circle
with 1 1/4" screw attached
to one end, to hold the insulator column to motor
mount. Position the hose
clamp on top of the motor
mount with the clamp section facing as shown in
Diagram 7. Loosen the
screw and square nut in
bracket to allow some
flexibility in positioning
bracket. Insert the long
PVC column into semicircular groove at rear of motor mount.
The wide black molded plastic ring is
at the top of the column. Line up Ushaped slots in the column ring with
the lower pulley and central motor
shaft. (The small holes are for inserting the upper comb.) Tighten the
screw and square nut on hose clamp
to allow the hose clamp to support the
column.
Make sure the column is straight.
Alignment of notches and motor shaft
is important since otherwise your generator will not work well. Keep looking down top of your column to make
sure notches and motor shaft are lined
up, as shown in Diagram 8. If column
has slipped, realign notches and pulley and refasten hose clamp.
11. Install upper comb.
Press two ends of upper comb into
two small holes in molded ring to top
of insulator column. Push in all the
way. See Diagram 9.
Diagram 9
9. Install upper pulley.
Lower (teflon) pulley has already
been installed on motor shaft. Should
you have any reason to install lower
pulley yourself, you must press firmly
until pulley is flush with sides of motor mount. Because lower pulley fits
snugly, you will need to use both
hands to press into place. Do not use
a hammer as it may damage motor
and shaft. Use a vice if necessary. We
use an arbor press in our plant.
To install upper (metal) pulley
assembly, take the rubber belt and
place one end over pulley. The pulley
assembly comes complete with center
shaft and plastic shaft supports. Place
attached shafts of upper pulley into
the U-shaped slots in the column top,
allowing the free end of belt to hang
down into column. See Diagram 9.
Diagram 8
Holes for
upper comb
Notch in ring
Lower
Pulley
Column
10. Position belt.
Using one hand to hold belt in
place on top of upper pulley, grasp
free end with other hand. Wrap free
end over lower pulley and adjust
again over top pulley. You must center belt around both pulleys so belt
will maintain a straight line. This is
needed for good operation.
12. Adjust upper brush.
It is important to adjust brush so it
almost but not quite touches belt and
upper pulley. Failure to adjust properly will affect the output and operation of your machine. Upper brush
comes with a supply of wire longer
than you need. Position wire strands
so they point toward center of pulley.
Use a scissors or cutting pliers
to trim and shape wire so brush is
within 1/8" of belt. Be careful not to
cut off too much. Brush may be adjusted somewhat by pressing it down
closer to belt. If you've made a mistake and brush is too short, you can
melt the solder, remove and reposition the brush, and then solder in
place again. You can also buy a replacement from us at nominal charge.
13. Test before installing
housing.
Plug into a grounded 110 volt 60
cycle typical household outlet
(10-066 uses 220 volt 50 cycle AC).
If it does not start automatically, gently stroke top pulley, unplug, replug
and try again. If it still doesn't run,
unplug, slip belt off lower pulley and
stretch it once by extending it out as
far as possible using a good firm pull.
Replace belt, plug in and try again.
14. Install housing.
Once your machine passes this
first test, unplug it and place housing
over entire unit by lining up two large
semicircular holes in housing over
cord and outer discharge electrode
11
(screw attachment with knurl nut.)
You also need to line up 3 smaller
holes in housing with remaining 3
holes in molded base. Housing will
rest on base but bottom of housing
will not be flush with base.
Attach housing by using 3 small
self-tapping screws (#20-1324). Use
screwdrivers to screw into place.
15. Install oblate.
Place elliptical oblate over the top
of the generator. "Dimple" in oblate
will rest on apex of triangular upper
comb assembly. Plug in generator to
grounded 110 volt 60 cycle outlet.
(220 volt outlet for 10-066.)
We are often asked if globes can
be used if dropped during experimentation. You can use any globe that is
not creased. Small dents should not
impair performance.
To install motor in older kits:
If you have a pre-1997 model, please
note that we have replaced the motor that
came with your kit with one with more
starting torque.
If you are replacing the old motor with
the new, follow the instructions below.
1. Place one 6-32 x 3/8" screw through
ground wire terminal. Loosely install
screw to motor. Place second 6-32 x 3/
8" screw through brush wire. Tighten
both screws.
2. Attach wires from motor to line cored
wires using 2 wire nuts.
If you have an assembled Van de Graaf
with an old motor and would like to
replace it with the stronger motor now
available, follow these instructions:
1. Unplug, remove housing. Remove 2
wirenuts from wires to motor.
Caution:
People with cardiac
pacemakers should never
operate the generator or
come in contact with it.
Discharge of static
electricity could cause the
pacemaker to be damaged
or to malfunction.
12
Science First®
Current Capacity of a Van de
Graaf Generator
The following calculations developed by
founder F. B. Lee refer to our 10-085
400,000 volt Generator. The method can
be used for any Van de Graaf.
Basic Equations:
Capacitance in micro faraday
= .0885 K A = C
T
K = 1.000 for a vacuum, almost the
same for air
A = Area in cm2
T = dielectric thickness.
Current flow through a capacitor =
I = C de or
I = E dC
dq
dq
C = capacitance in farads,
E = potential in volts;
I = current in amperes.
For air, maximum voltage difference
is 30,000 volts/cm.
E thus is 30,000
T
Combining:
I = .0885 K d A E x 10 -12 amp
T dθ
since E is 30,000 volts
T
cm
I = (.0885) (30,000) 10 -12 dA
dθ
For 1 microamp:
dA = 10-6 = 339 cm2 or 52.5 sq in/sec
For motor speed:
3000 RPM (50 rev/sec)
Pulley diameter 1.5"
Belt width 2"
I = (50) (1.5 π) (2) = 9.0 microamps
5.25
(theoretical)
Pulley curvature affects this result. It
is less at small diameters because 30,000
volt/cm is only for flat surfaces.
Between 25 cm spheres = 29,400
volts/sec
Between 10 cm
= 28,500
Between 5 cm
= 28,200
Between sharp point
= 11,500
Pulley at top also generates a theoretical 9 microamps.
Probable cause of short fall from 18
microamps:
(1) Part of 30,000 volt/cm is voltage
difference between sides of bolt;
(2) Curvature of pulley;
(3) Nearby points or edges
P/N 24-1060
©Science First® is a registered trademark
of Morris & Lee, Inc. All rights reserved.
Revised 4-05
What To Do If Your
Generator Does
Not Work
1. Check loose, worn, frayed wires.
Replace defective parts.
2. Check humidity. See if you can
dry out the inside your generator
with a hairdryer or operate on
low-humidity days.
3. Loosen the belt. Take it out and
stretch it twice to about double its
length. Do not overstretch. Belts
may be brittle and break.
If the belt has been exposed to
cold weather, you can thaw it out
in hot water.
4. Remove lint from belt, housing
and globe. Wash belt in soap and
water. Rinse and dry thoroughly.
Lint drains your output. (For globe
and housing, you may use a
dishwasher.)
5. Wipe upper pulley with alcohol.
Remove upper pulley, wipe all
surfaces and replace. Belts vary in
composition and sometimes leave
a film or residue on the pulley
which drains charge. Lower pulley
is teflon and is not affected.
6. Adjust brushes.
There may be too much clearance
between belt and wire combs.
Adjust combs by bending until
they come within 1/8" (3 mm) of
the belt but do not touch the belt.
If you have cut your brush too
much, order a replacement.
7. Allow warm-up period. Let your
generator run a few minutes
before experiment. This often
offsets high humidity. You can dry
the inside of the column with a
hair dryer before experimenting.
8. Maintain regularly. Lubricate
upper pulley bearings with a drop
of oil yearly. Wash belt after 50
operating hours with soap, rinsing
thoroughly. To clean upper
pulleys, use rough cloth, sand
paper, scotchbrite or steel wool to
wipe off any deposits caused by
wear. Clean the lower pulley with
a clean cloth.

10-065 Van de Graaf Generator Instructions

Transcription

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