Mechanisms for Transfer of Charge Restless Electrons Mechanisms for Transfer of Charge

Conductive Properties of Solids Friction : rubbing two electrically neutral objects together can charge both objects – they will gain OPPOSITE charge in EQUAL amounts. Conductive Properties of Solids metal alloys special When two insulators are rubbed together – the one with greater RESISTIVITY will tend to gain ELECTRONS while the other loses them. metals silicon wood rubber sea water pure water SUPER CONDUCTORS SEMI INSULATORS CONDUCTORS CONDUCTORS Conductors Do NOT hold onto charge well because it flows through them very easily High Conductivity Insulators Readily hold onto charge because it is difficult for charge to flow through them High Resistivity

Friction HIGHER RESISTIVITY

Stick Tape Video http://phet.colorado.edu/en/simulation/balloons

Grounding Grounding a charged object makes it neutral Since the Earth is so large it can: ABSORB excess electrons from negatively charged objects RELEASE free electrons to positively charged objects Grounding a charged object makes it neutral One symbol that is often used to show that something is grounded is:

Induction Negative To Neutral Induction : a charged object comes near another object WITHOUT TOUCHING – causes it to POLARIZE Induction Negative To Neutral - Polarization + - Excess electrons exert force against nearby electrons in the neutral object

Induction Positive To Neutral + Polarization - + Electrons in the neutral object experience an attractive force, which pulls them closer to the charged object

Conduction Negative To Neutral Conduction : a charged object TOUCHES another object – electrons jump from one to the other in an attempt to EQUALIZE the charge on both objects. Conduction Negative To Neutral - - Excess electrons exert repulsive forces on one another, causing them to move apart as much as possible BOTH now have the same charge!

Conduction Positive To Neutral + + Electrons in the neutral object experience an attractive force. They neutralize some of the positive charge, leaving both with a lack of electrons BOTH now have the same charge!

- - - - - - - Electroscope An electroscope is a device that detects CHARGE - - - - - When the scope is CHARGED, the LEAVES at the bottom will REPEL one another The charged LEAVES exert force on one another, forcing them apart - -

Electroscope – negative cond. Step 5 Scope is once again neutral – excess electrons are gone Step 3 Scope is now negatively charged Step 4 Scope is grounded allowing electrons to escape Step 1 Negative rod touches neutral scope Step 2 Electrons spread out and charge plates - - - - - - -

Electroscope – positive cond. Step 4 Scope is grounded – electrons from the ground are attracted to the positive scope Step 5 Scope is once again neutral – balanced charge is restored Step 2 Electrons leave scope because they are attracted to the positive rod Step 3 Scope is now positively charged Step 1 Positive rod touches neutral scope + - + - - - - + - +

Electroscope – negative ind. Step 3 Rod is removed – electrons are attracted back to the top and “re-neutralize” the electroscope. Step 2 Scope polarizes as electrons at the top try to move away from the charged rod. Step 1 Negative rod brought near grounded scope - - + -

Electroscope – positive induction Step 3 Rod is removed. Electrons are attracted back into the leaves by the protons, making the electroscope neutral again. Step 2 Electrons from the bottom of the electroscope are attracted to the positive rod – get pulled up. The leaves get a positive charge on them. Step 1 Positive rod is brought near neutral electroscope + - + - +

Electroscope – ind. with ground Step 3 Ground is removed while the rod is still nearby, keeping electrons from re-entering the scope Step 5 The rod is taken away and the positive charge remains on the scope Step 4 Scope now has a charge that is opposite to the charge on the rod Step 2 Excess electrons from the rod force electrons from the scope into the ground. Step 1 Negative rod brought near grounded scope - + - - + - +

Electroscope – ind. with ground Step 3 Ground is removed, while the rod is still nearby, pulling on electrons and keeping them from escaping Step 4 Scope is now negatively charged – the opposite charge as that of the rod Step 5 Rod is taken away and the negative charge remains on the scope Step 1 Positive rod is brought near grounded scope Step 2 Electrons from the ground are attracted to the positive rod + - - -