Static Electricity and Charging Field Theory

Static Electricity Look up the following key terms/law: Ion Elementary Charge Conductor Insulator Law of Conservation of Electric Charge

Static Electricity Law of Conservation of Electric Charge –when charging objects by rubbing, the net change in the amount of charge is zero. Structure of the atom –positively charged nucleus –surrounded by one or more negatively charged electrons Only electrons move in solid objects

Key Terms Ion – atom which has gained or lost an electron Elementary charge – the magnitude of the charge on ONE electron or proton Conductor – many of the electrons are bound very loosely to the nuclei and can move about freely Insulator – almost no loosely bound electrons

How do you charge an object? 3 ways: –Friction: objects can be charged by rubbing them together to exchange charge –Conduction: electrons are transferred to or from a charged object to a neutral object –Induction: charged object is brought near neutral object. Electrons in the neutral object redistribute themselves

You Try It Charge by Friction: –Rub wool along a balloon (etc) Conduction: –Touch an electroscope Induction –Stick a balloon to the wall

Quick Lab How does an electroscope work? –An electroscope will move when there is a non-neutral charge –Example: A neutral electroscope’s metal “pole” will turn if you put a charged item near or touching it.

Electroscope

Difference between induction, conduction, and friction charging: –Friction: objects can be charged by rubbing them together to exchange charges (one item will be + and one – charged) –Conduction: electrons are transferred to or from a charged object to a neutral object –Induction: charged object is brought near neutral object. Electrons in the neutral object redistribute themselves. –*** Induction: The object is not actually charged!!! Just appears to be in different parts of the object. –

What happens when you move your hand close to the electroscope? If the electroscope is not charged –Nothing! Your hand is neutral. –If the electroscope is charged The electroscope will deflect from your neutral hand as your neutral hand will redistribute the electrons. It will go back once your move your hand away as it is still charged.

What happens when you touch the electroscope? Why? If you touch the electroscope and it is not yet charged nothing as both are neutral. If you touch the electroscope and it is charged, your hand will “ground” it or make it neutral by allowing electrons to travel into or out of the electroscope.

How do you charge an electroscope positively? Put your hand on the electroscope to allow movement of electrons At the same time put a negatively charged object near the electroscope (inductive charging) Remove hand then remove the negatively charged object V96dKQhttps:// V96dKQ

OR Contact a positively charged object to the electroscope

How do you charge an electroscope negatively? Contact a negatively charged object to the electroscope OR…

What happens when you touch the electroscope and it is already negatively charged? You ground the electroscope. It will be neutral. Electrons will escape through you hand. ONLY ELECTRONS MOVE

What happens when you touch the electroscope and it is already postively charged? You ground the electroscope. It will be neutral. Electrons will come through you hand into the electroscope. ONLY ELECTRONS MOVE

What works best for charging? Why do you think this is? Depends on situation but if you want a more “permanent” charge it must be conduction or friction. Different materials will make charging easier. –Materials that tend to gain or lose electrons include wool, human hair, dry skin, silk, nylon, tissue paper, plastic wrap and polyester (depends on the material’s electron affinity) – a.cfmhttp:// a.cfm

How does a van der Graaf generator work? A3pgkQhttps:// A3pgkQ A3pgkQhttps:// A3pgkQ

If an object is positively charged what will it attract? Negatively charged Neutral (if it is charged inductively)