110 likes | 294 Views
Charging by Contact and by Induction. Detecting Charges. Electroscope: A device that detects the presence of electric charges Pith Ball Electroscope: A small light conductive ball suspended by a cotton thread When a charged object is brought near the pith ball, it causes it to move
E N D
Detecting Charges • Electroscope: A device that detects the presence of electric charges • Pith Ball Electroscope: A small light conductive ball suspended by a cotton thread • When a charged object is brought near the pith ball, it causes it to move • Metal leaf electroscopes have a sphere connected to a rod with metal leaves attached to it (all made of metal). • The leaves spread apart when a charge is near the sphere
Charging by Contact • Takes place when contact is made between a neutral object and an object that is charged • On contact, electrons flow from the negatively charged object into the pith ball • After contact, both the object and pith ball have a negative charge
The Laws of Electric Charges • An object may be electrically neutral, negatively or positively charged • The charge on an object is determined by the electrons (they can move from one object to another) • 3 Laws: Like charges repel, opposite charges attract and charged and neutral objects attract each other
The Amount and Type of Charge • Amount of charge depends on the difference between the number of protons and electrons • The size of the electric force is directly proportional to the amount of charge on each object • As the distance between two charged objects increases, the electric force decreases • To determine if an object is charged and what type of charge, you must observe repulsion between it and another object
Electric Fields • Electric Field: An electric force that exists between two objects that are not in contact if at least one of them is charged • Objects with greater charges have stronger electric fields • electric forces are transmitted at the speed of light
Charging by Induction • When a charged object is close to a neutral one, the electric field of the charged object produces a force on the neutral object - the force is attractive • Induced Charge Separation: The movement of electrons in a substance caused by the electric field of a nearby charged object without direct contact between the substance and the object