PHY122_L04 - PHY122 Physics for the Life Sciences II PHY122...

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HY122 HY122 - hysics for the Life Sciences II PHY122 PHY122 Physics for the Life Sciences II Physics for the Life Sciences II Lecture 4 Electric Energy and the Electric Potential Capacitors Lecture 4 1 09/08/2011
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Channel Setting Instructions for ResponseCard ResponseCardNXT NXT 1. Press and release the “ Channe l" button. 2. Use the number pad to enter the 2 digit channel code (i.e. channel 21 = 21): ur Channel is 21 Our Channel is 21 nce the channel number has been typed press 3. Once the channel number has been typed, press the (c)enter button. The should appear to confirm success. 09/08/2011 Lecture 4 2
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Recap: Q Coulomb Force (for point charges): Field: E F / q xamples: 2 0 1 4 qQ F r  1 Q 1 Q 1 Q examples: otential (“ olatage ifference”) across the plates of a point or 2 sphere 0 ; 4 E r single plane 0 ; 2 E A  capacitor 0 E A Potential ( volatage difference ) across the plates of a charged capacitor: pacitor elec U Fd WQ E d d  Energy: capacitor 0 VE qq q A ; Uq V  09/08/2011 Lecture 4 3
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Choose the correct answer … The Voltage across the terminals of an (unconnected) capacitor depends … 66% 1. Only on the charge Q 2. Only on the plate-to- late distance plate distance d 3. Only on the area A of the plates 4. On all three quantities Q , A , and d 5% 3% 2% 1% 12% 11% 5. On Q and A alone 6. On Q and d alone n nd lone 09/08/2011 Lecture 4 4 1234567 7. On A and d alone
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Allesandro Allesandro Volta Volta Inventor of the electro-chemical battery – a pile of cells made of a zinc electrode and a copper electrode, separated by card board saturated with sulfuric acid or a brine mixture of salt and water. – The electrolyte exists in the form 2H + and SO 4 2– . The zinc, which is higher than both copper and hydrogen in he electrochemical series reacts with the negatively Alessandro Volta the electrochemical series, reacts with the negatively charged sulfate ( SO 4 2– ). – The positively charged hydrogen ions ( protons ) capture electrons from the copper, forming bubbles of hydrogen (1745-1827) gas, H 2 . This makes the zinc rod the negative electrode and the copper rod the positive electrode. – Essentially, the difference in electro-chemical ionic inding energies provides the charge umping action ! binding energies provides the charge-pumping action ! – We now have two terminals, and the current will flow if we connect them. The reactions in this cell are as ollows: follows zinc Zn Zn 2+ + 2e sulfuric acid 2H + + 2e H 2 09/08/2011 Lecture 4 5
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