NEW ZEALAND TARANAKI


You can build your own static electricity detector ...

Static shocks shoppers in Supermarket

"Customers heading for New Plymouth's newest supermarket really are in for a shock.

Due to an unexplained static electricity problem, dozens of shoppers have literally buzzed while doing their weekly shop at Countdown Waiwhakaiho.

Static electricity was caused, in simple terms, when electrons were transferred from one object to another by things rubbing together, Mr Fenton said.

The teacher and some students plan to head to the store on Sunday with a static field detector to find out more."

source; Taranaki Daily News,  21 August 2009

The static electricity sensor used by the students




But  what does friction have to do with lightning or electicity?


Friction and Electric Charges:

Whenever two object rub together, electrically charged particles call electrons are lost from one object and transferred to the other. The electrons will try to get back, attracted to the now positvely charged object by an invisible force.

(A bit like North and South poles of a magnet)

This electric force can be felt as "static electricity" that can make your hairs stand on end! Ever felt this from a TV or from a woollen jersey (jumper)?

A man-made lightning storm:

A special lightning machine called a Van de Graaf generator uses friction (rubbing) to generate lots of static electricity. Here the electrons can be seen leaping back to where they came from as a huge spark...a lightning bolt!
The static electricity from this machine is safe to touch...Mikaela is quite happy! Her whole body and the hairs on her head have the same electric charge so push away from each other...a bit like two North poles on a magnet push away...

What creates thunder and lightning?

We said that two objects rubbing together create static electricity. Think about the clothes coming out of a tumble dryer...sometimes a sock is "stuck" to a jersey...as you pull the sock off you can here the crackle of electricity as tiny bolts of lightning return electrons to where they belong. What about at night when your remove a woollen jersey? The same sort of rubbing on your body creates the same sort of tiny lightning bolts.

Lets think BIG! Imagine the whole sky; the air (as wind) rubbing against trees, houses, people, the oceans, creating static electricity...LOTS of it! This electricity finally is able released as a giant electric spark...lightning. Unlike our Van de Graaf machine, lightning electricity can kill!

Here is a neat little circuit that can show how far the invisible lines of electric force can reach due to static electricity .

static electricity sensor
A field effect transistor (FET) is connected to a Light Emmitting Diode (LED). One leg of the FET acts as an antenna, able to switch the LED on (or off!) depending on the type of electric field nearby.

Note that we added a 1 mega ohm resistor  going from the antenna to the FET. The antenna can be cut to a length that suits the sensitivity desired.

Even simple walking generates an electric field that can be detected with this circuit.

  • Negatively charged objects turn the LED off, it lights again when the object is removed.
  • Positively charged objects make the LED brighter, then it goes dark when the object is removed.


FIND OUT MORE:-

  1. Can you detect the electric field generated by someone combing their hair at the other end of the room?
  2. Carry out a survey of items and places that generate static...does your supermarket shock its shoppers?
  3. Can you detect a field (the LED lights up) from a nearby object and see what happens when someone walks inbetween it and the sensor? Can you use this as a simple alarm system?
  4. Build sensors to detect acidity, temperature, infra-red, conductivity, etc
  5. How are electric, magnetic and gravitational fields similar? Different?
  6. Use magnets to build a motor and a generator.

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