22_Current_and_Resistance

22_Current_and_Resistance - Electric Current and Resistance...

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1 Electric Current and Resistance Current Parts of a circuit Resistivity Ohm’s Law Ohmic and Nonohmic materials Energy and Power
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2 Electric Current • Electric current is the movement of electric charge • Very important in our lives – we use it to deliver energy and information
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3 Current in Conductors • Current in conductors is produced by electrons moving through a lattice of fixed ions • Current is a drift of the sea of electrons through the lattice • Lattice is not charged
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4 Creating a current in a wire • Currents are created by an electric field pushing the electrons along a wire • The electric field is produced by a potential difference along the length of the wire like a capacitor or a battery
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5 Conservation of current • Follows from the conservation of charge • The current is the same at all points along a wire • Similar to a water turbine, same amount of water in as water out
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6 Definition of Current Current, I, is defined as the rate of change of positive charge: t Q I Units: Coulombs/second or Amperes or Amps
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7 Definition of Current Current, I, is defined as the rate of change of positive charge: t Q I Units: Coulombs/second or Amperes or Amps
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8 Conservation of current: Kirchhoff’s Law The sum of currents into a junction must equal the currents flowing out of it   out in I = I j j I 0 Sometimes expressed as:
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9 Example of Kirchhoff’s Law What are the currents in B and C ?
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22_Current_and_Resistance - Electric Current and Resistance...

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