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Transcript
AP Physics Chp 18 • Crooke’s Tube allowed Thomson to show that atoms possessed smaller particles that also had an electric charge • Electrons • Protons • Neutrons were later • Millikan determined the charge using oil drops • e = 1.60 x 10-19 C • Why do we call the +1 for protons and -1 for electrons? • Like charges repel and unlike attract • Within an isolated system the net charge remains constant ie. Rubbing a balloon on your hair • Conductors – allow charge to pass thru • Insulator – do not allow charge to pass thru • Charging by contact – balloon and hair • Charging by induction (coming close) – There has to be a way to allow the opposite charge to leave the object to maintain the charge • Coulomb’s Law F k q1 q2 r 2 • k is 8.99 x 109 Nm2/C2 • Can be either attractive or repulsive unlike gravity • How much force exists between two protons in the nucleus of helium if they are 3.1 x 10-15 m apart? • What’s the gravitational force? • mp = 1.67 × 10-27 kg • Electric Field F E qo • qo is a small, positive test charge • E goes in the same direction as F if qo is + • How large is the electric field that levitates a proton in the air? m = 1.67 x 10-19 kg and q = 1.6 x 10-19 C • For a point charge Ek • IF q is + then E is away from qo q r 2 • Parallel plate capacitors q E o A E o σ is the q/A (charge density) • Electric Field Lines ( lines of force) • They go away from + towards – • Don’t stop mid-way • More charge = more lines