What is an Electric Charge? • Protons have positive (+) electric charge • Electrons have negative (-) electric charge.
What is an Electric Charge? • Atoms become charged by gaining or losing electrons. • Static electricity —the accumulation of excess electric charges on an object.
Calculating Charge • Electric charge was quantified by Robert Millikan in 1909. Atomizer + + + + - charge On - - - - Battery
Calculating Charge • Millikan discovered that all the oil droplets had a charge of 1.60 x 10-19 Coulombs (C) or multiples of this charge. Electron = -1.60x 10-19 C Proton = +1.60x 10-19 C Neutron = 0 C
Charged Objects - - + • Electrically charged objects obey the following rules: - Law of conservation of charge- charges may be transferred, but they cannot be created or destroyed. • Opposite charges attract, and like charges repel.
Charged objects • How are these charges able to move towards or away from each other? Electrical force: force that is exerted by + and – charges on one another. • Like gravity, electrical force is a “field force” – force without physical contact • Objects placed close together will experience a greater force – Coulomb’s Law
Charged objects Coulomb’s Law Felectric = Kc [(q1q2 )/r²] Kc = Coulomb constant = 8.99 x 109 N • m²/C² q = charge r = distance between the two charges
Transferring Electric Charge • Charging by contact • The process of transferring charge by touching or rubbing • Example: static electricity from your feet rubbing the carpet • Works best on non-conductive materials.
Transferring Electric Charge • Charging by induction • The rearrangement of electrons on a neutral object caused by a nearby charged object. Occurs in conductors! - + - + - - - - + - - Charged Object + Conductor
Transferring Electric Charge • Charging by Polarization • Same concept as induction, but in insulators! • The rearrangement of electrons on a neutral object caused by a nearby charged object. =neutral = - - - - - - - - - = + Charged Object Charged Object Insulator
Transferring Electric Charge • Static discharge • A transfer of charge through the air between two objects because of a buildup of static electricity. Example: lightning • Grounding—using a conductor to direct an electric charge into the ground.