Transcript Van de Graaff Generator - Talkington YWL AP Physics 1

Van de Graaff Generator
Goals
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Learn how a Van de Graaff generator
works and what it is used for
Explain demonstration/experiments that
involve the Van de Graaff generator
What is it?
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The Van de Graaff generator is a device
that separates electric charges
mechanically.
This produces a high voltage with a low
current.
Low current means its safe to learn with!
How much voltage?
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Voltage is…is commonly used as a short
name for electrical potential
difference
Which means is a measurement of the
energy contained within an electric field,
or an electric circuit, at a given point
This VdG generator can produce anywhere
from 10-200 thousand volts (V).
It is safe because the current is quite low.
What does it look like inside?
Metal Sphere
Insulating tube
Conveyor belt (rubber)
Metal Combs
Base (Electric motor)
Electrons jump off
the belt at the top
Electrons jump
onto the belt at the
bottom
How does it work?
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The VdG generator is a charge separator.
When turned on, the belt begins to move,
picking up negative charges deposited by the
metal comb at the base.
The belt then transfers the charges to the metal
comb at the top of the generator.
The metal comb is attached to the metal sphere
and thus transfers the negative charges to the
sphere.
How is the VdG like the cashier’s
check out at the grocery store?
Think of the groceries
as charges.
Metal Sphere
Insulating tube
Base (Electric motor)
Discharging The VDG
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By completing the circuit, we neutralize
the static charges!
Touch the wand to the VDG
Safety
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Do not allow students to use the Van de Graaff generator
unsupervised.
People with cardiac pacemakers should never operate the
generator or come in contact with it.
Still, we are dealing with high voltage here. Stay about three feet
away from the collector while it is charged, or unless instructed
otherwise.
Always discharge the collector dome between experiments and
when you are finished.
The motor produces a lot of heat that could damage the belt or
the motor itself. Do not run the generator continuously for long
periods of time.
Leave the upper and lower combs alone.
Keep the entire device clean and dry.
Handle the aluminum parts with care.
What is it used for?
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Used during early research into radioactivity and
atomic structure, used as power source for
particle accelerators.
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Still used to power high energy x-ray machines
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Useful in laboratory study of electrostatics
VdG Demos
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Mop Head
Sparks!
Flying Pie
Crazy Hair
Shock Line
Mop Head
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The charge stays there when the power
is turned off – that’s why it’s called static
electricity!
When there is no net charge present, the
mop strands fall down - the charges has
been neutralized, or rather, discharged
VdG Demos
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Mop Head
Sparks!
Flying Pie
Crazy Hair
Shock Line
Sparks!
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You can see a brief glimpse of static
discharge!
The light bulb lights up because on
electrons are need to carry electricity –
No protons required
VdG Demos
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Mop Head
Sparks!
Crazy Hair
Flying Saucers
Shock Line
Electrons Flow out!
Hair stands up because the electrons trapped in
your hair are repelling each other!
VdG Demos
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Mop Head
Sparks!
Crazy Hair
Flying Saucers
Shock Line
Flyin’ Pie!
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The pie tins fly away because as they gain
a negative charge due to transferring
electrons – the repel each other!
Back to law of charges!
VdG Demos
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Mop Head
Sparks!
Crazy Hair
Flying Saucers
Tinsel Time
Shock Line
Push/Pull?
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When I hold them, the tinsel has a
positive charge, so it pulls towards the
VdG generator.
When it touches and gains a negative
charge – it immediately is repelled by the
negative charges!
VdG Demos
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Mop Head
Sparks!
Crazy Hair
Flying Saucers
Tinsel Time
Shock Line
Shocking!
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They human body makes an excellent
conductor – not because of water, but
because of the electrolytes stored in our
bodies’ water!(We are about 70 percent
electrolitic water!)
When the discharge occurs, everyone gets
discharged!
Questions for Test on Monday
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Explain in your own words how the VdG generator
works.
Be sure you can explain in words and using a diagram
how:
a. Someone’s hair can stand up
b. How a shock can occur
c.
How something can be repelled by the VdG