 Materials can roughly be divided into three categories:  Conductors - which easily transport electrons without trying to capture or impede them, Topic 6.2 Extended A – Electrostatic charging  Nonconductors or insulators - which capture or impede electrons,  Semiconductors - which lie between conductors and insulators.  A simple charge detector called an electroscope can be made using a glass flask, and a rubber cork (both insulators).  A metal rod with two very thin metal leaves is then placed inside the flask, exiting via the cork. Usually a metal bulb is placed on the exposed end of the rod. These components are all conductors.  The thin metal foils hang straight down if there is no net charge on them.

Topic 6.2 Extended A – Electrostatic charging  We use the electroscope to observe charge phenomenon.  For example, if we place a negative charge near the bulb (without touching it) we will observe the following reaction:  How do you explain this?  If we place a positive charge near the bulb (without touching it) we will observe the following reaction:  How do you explain this? F UN W ITH T HE E LECTROSCOPE FYI: The charged rubber or glass rods are charged by rubbing them with silk or wool. Friction transfers electrons from one to another. FYI: In these experiments, the electroscope received no net charge. It began neutral, and ended neutral.

Topic 6.2 Extended A – Electrostatic charging  For example, if we place a negative charge on the bulb we will observe the following reaction:  How do you explain this?  If we place a positive charge on the bulb we will observe the following reaction:  How do you explain this? FYI: In these experiments, the electroscope received a net charge. It began neutral, and ended charged. F UN W ITH T HE E LECTROSCOPE FYI: We call this process CHARGING BY CONTACT. Note that the charge source touches the electroscope.

 Observe the electroscope.  Is it charged, or is it neutral? Topic 6.2 Extended A – Electrostatic charging  Can you tell whether it is a positive charge?  Can you tell whether it is a negative charge?  Observe:  Can you tell whether the charge is positive or negative now?  How do you explain this? F UN W ITH T HE E LECTROSCOPE

 Observe the electroscope.  Is it charged, or is it neutral? Topic 6.2 Extended A – Electrostatic charging  Observe:  Can you tell whether the charge is positive or negative?  How do you explain this? F UN W ITH T HE E LECTROSCOPE  Is it charged, or is it neutral? FYI: We call this process CHARGING BY INDUCTION. Note that the charge source never touches the electroscope.

 Polarization occurs when charge is redistributed on an object, but not added or removed. Topic 6.2 Extended A – Electrostatic charging P OLARIZATION  For example, if a charged balloon is held near a wall, the charges in the wall redistribute themselves, causing the balloon to be attracted to the wall  The balloon sticks. Why? FYI: Note that the wall is still neutral. It has been polarized.