Van de Graaff Generator

Goals 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? 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? 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? 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 By completing the circuit, we neutralize the static charges! Touch the wand to the VDG

Safety 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? Used during early research into radioactivity and atomic structure, used as power source for particle accelerators. Still used to power high energy x-ray machines Useful in laboratory study of electrostatics

VdG Demos Mop Head Sparks! Flying Pie Crazy Hair Shock Line

Mop Head 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 Mop Head Sparks! Flying Pie Crazy Hair Shock Line

Sparks! 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 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 Mop Head Sparks! Crazy Hair Flying Saucers Shock Line

Flyin’ Pie! 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 Mop Head Sparks! Crazy Hair Flying Saucers Tinsel Time Shock Line

Push/Pull? 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 Mop Head Sparks! Crazy Hair Flying Saucers Tinsel Time Shock Line

Shocking! 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 Explain in your own words how the VdG generator works. 2. Be sure you can explain in words and using a diagram how: Someone’s hair can stand up How a shock can occur How something can be repelled by the VdG