chapter25

# chapter25 - )dica gnorts a netfo etylortcele dellac yrettab...

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How do we charge a capacitor? People knew how to make a brief spark, but not how to keep charges moving. Volta invented the battery in 1800’s. - - - - + + + + Liquid or Paste inside battery called electrolyte (often a strong acid) Two metal plates are called electrodes. Battery Device that generates and maintains an electrical potential difference.

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By using two different metals for the electrodes, we can have two different chemical reactions. The reactions build up charges creating the electrical potential difference between the metal electrodes. One unit is called a “cell”. Many cells put together is called a battery. Example: Car battery is six 2 V cells = 12 V battery Battery Each cell consists of a lead (Pb) electrode and a lead oxide (PbO 2 ) electrode immerse in a solution of water and sulfuric acid (H 2 SO 4 ). The “Mac Gyver” Battery
EMF When the battery is not connected, the charges have nowhere to go: they feel a potential, but they stay in the electrodes When we “close” the circuit, charges can move, can circulate, producing a “current” Analog between a battery and an escalator. --------------------- +++++++++++++ + + + V bat Electro motive force (EMF)

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Charging a capacitor The electrons will flow through the wires. However, they cannot jump through the empty space between the plates. Charges will accumulate in the plates until the potential difference or voltage equals the one in the battery. Electric current 8 = = dt dQ t Q I Rate of flow of charge Units [ I ] = Coulombs/second = Ampere (A) or “Amp”
Electrons flow in metals, not the protons, so the negative electric charges are moving. -e E E e E q F v v v = = Electrons go “upstream” against the electric field vector. What or “who” is carrying the current? Flow of negative charge in one direction is equivalent to flow of positive charge in the opposite direction.

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