What is Static Electricity? Static electricity is an imbalance of positive and negative charges on an object. Charges on Objects An object may be positively charged, negatively charged, or neutral. An object becomes charged when electrons are either removed from or added to the object.

- - - Neutral object + number of protons = number of electrons + Positively charged object number of protons > number of electrons + - Negatively charged object number of electrons > number of protons

Law of Electric Charges A charged object exerts an electric force on a nearby object. The force either attracts or repels the nearby object. The Law of Electric Charges states that: opposite charges attract each other objects with like charges repel each other charged objects will attract neutral objects

Detecting the Charge on an Object: Electroscopes An electroscope is a device that is used to detect the presence of electric charges. There are two types of electroscopes: pith ball electroscope metal-leaf electroscope

With an electroscope you can determine if an object is neutral or if the object has a charge on it. You do this by observing what happens when the object is brought close to a neutral electroscope.

Pith ball electroscope This electroscope consists of a small ball made of pith or cork or Styrofoam hanging from a thread. If object is neutral, the pith ball does not move If object is positively or negatively charged, the pith ball swings toward object

Metal-leaf electroscope This electroscope consists of a metal ball connected to two thin metal strips. If object is neutral, the metal leaves hang straight down If object is positively or negatively charged, the metal leaves spread apart

Homework p471 #3-9