Ch. 17-1Electric Charge PreAP Physics Allen High School
How do you acquire charge? • Conservation of Charge • Bad Hair Day? • Permanent? • Grounding—giving or takingan infinite number of electrons.
What is Charge? • Proton • Neutron • Electron • Variable: qUnit: Coulomb (C) • Another common unit: μC
Charged Objects • Positive object = • Negative object = • Neutral object = • Equilibrium • Not necessarily zero. • The only charges that can move are ____________.
Electron Flow • Conductors • Insulators
Separating Charge • Conduction (not the heat transfer) Contact between certain materials will separate charge. • Dragging/rubbing speeds up the transfer of electrons.
Separating Charge • Polarization • Electrons shift within the object, but are not transferred. • Think of water’s polar nature.
Separating Charge • Induction • Forcing a set charge on an object by giving an alternate path for charges to flow. • Only works for conductors. • Induces a charge opposite the first charged object.
Who is Robert Millikan? • Millikan’s Oil Drop Experiment proved that charges are quantized, which means they are whole multiples of the fundamental charge. • “Discrete amounts in nature.” • He also found that a proton has a charge equal and opposite to an electron. • qp = + 1.6 x 10-19 C
Electric Charge • Electrons are the only charges that can move, or flow from one material to another. • When you scuff your feet, you borrow electrons—can be a little or a lot. • 1e = 1.6 x 10-19 C (smallest amount) • Charged objects are in multiples of e.
Example 1 • You rub a balloon on your head and acquire a charge of 4.6 μC. How many electrons did you borrow? • Which object is positive? • Which object is negative?
Example 2 • What is the charge of an object that gains 1.2 x 108 electrons?