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Capacitors and/or TV (not Emf)

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1. An empty capacitor does not resist the flow of current, and thus acts like a wire. 2. A capacitor that is full of charge will not allow current to flow, and thus acts like a broken wire. RC CIRCUITS

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When the switch is closed, the capacitor will begin to charge. RC Circuits

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If an isolated charged capacitor is connected across a resistor, it discharges: RC Circuits

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A battery with an emf of 24 V and an internal resistance of 1 Ω is connected to an external circuit as shown above. 1990B3 p.47

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a.Calculate the equivalent resistance of the combination of the 4 Ω, 8 Ω, and 12 Ω resistors R S = = 12 Ω = 6 Ω 1990B3 p.47

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b.Calculate the current in the 5 Ω resistor R E = = 12 Ω = 2 A

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c. Calculate the terminal voltage, V AC of the battery V T = E - I r = 24 V - (2 A) (1 Ω ) = 22 V 1990B3 p.47

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d. Calculate the rate at which energy is dissipated in the 12 Ω resistor P = I 2 R = (1 A) 2 (12 Ω ) = 12 W Current splits at B with 1 A through each branch 1990B3 p.47

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e. Calculate the magnitude of the potential difference V BC V BC = I R = (2 A) (6) Ω = 12 V 1990B3 p.47

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In the circuit shown above, A, B. C, and D are identical light bulbs. Assume that the battery maintains a constant potential difference between its terminals (i.e., the internal resistance of the battery is assumed to be negligible) and the resistance of each light bulb remains constant. 1998B4 p.58

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a. Draw a diagram of the circuit in the box, using the symbols to represent the components in your diagram. Label the resistors A, B. C, and D to refer to the corresponding light bulbs. 1998B4 p.58

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b. List the bulbs in order of brightness, from brightest to least bright. If any two or more bulbs have the same brightness, state which ones. Justify your answer. A > D > B = C A has the largest current V D = V C + V B so D is brighter than C or B C and B are in series = same current 1998B4 p.58

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c. Bulb D is then removed from its socket. i. Describe the change in the brightness, if any, of bulb A when bulb D is removed from its socket. Justify your answer. The brightness of bulb A decreases. R Eq increases, I A decreases 1998B4 p.58

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ii. Describe the change in the brightness, if any, of bulb B when bulb D is removed from its socket. Justify your answer. The brightness of bulb B increases. The current through bulb B increases, voltage across B increases 1998B4 p.58

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A circuit contains two resistors (10 Ω and 20 Ω) and two capacitors (12 μF and 6 μF) connected to a 6 V battery, as shown in the diagram above. The circuit has been connected for a long time. 2003B2 p.47

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a. Calculate the total capacitance of the circuit. = 4x10 -6 F 2003B2 p.47

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b. Calculate the current in the 10 Ω resistor. = 0.2 A 2003B2 p.47

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c.Calculate the potential difference between points A and B. V AB = V 20 = IR 20 = (0.2 A)(20 Ω) = 4 V 2003B2 p.47

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d.Calculate the charge stored on one plate of the 6 μF capacitor. Q = C T V = 4x10 -6 F (4 V) = 16x10 -6 C 2003B2 p.47

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e.The wire is cut at point P. Will the potential difference between points A and B increase, decrease, or remain the same? Justify your answer. ___increase ___decrease ___remain the same No current flows through A-B so it does not affect the potential difference 2003B2 p.47

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