# capa07 - Solution Derivations for Capa#7 1 Consider the...

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Solution Derivations for Capa #7 1) Consider the behavior of the circuit, when various values increase or decrease. (Select I-increases, D-decreases, If the ﬁrst is I and the rest D, enter IDDDD). QUESTION: A) If R1 decreases, the current through R3 . B) If R3 decreases, the current from the battery . C) If R6 decreases, the power output from the battery . D) If R1 decreases, the current through R6 . E) If the voltage V decreases, the total current from the battery . F) If R3 decreases, the current through R4 . ANSWER: A) Increases, The equivalent resistance of the parallel resistor decreases. From V = IR , the current will increase. B) Increases. Same as (A). C) Increases. P = IV . If the current rises due to a decrease in resistance, the power will also rise. D) Increases. See (A). E) Decreases. Less voltage to push current through the circuit. F) Decreases. More will want to ﬂow through R3 with a now lower resistance. 2) A battery with an emf of 12 . 00 V has an internal resistance r . When connected to a resistor R the terminal voltage is 11 . 70 V and the current is 0 . 11 A . What is the value of the external resistor R? Use “Ohm” as units of resistance. V E = Given (EMF) V = Given I = Given r = ? R = ? 1

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To solve this problem, you don’t have to worry about the internal resistance. Thus, Ohm’s law applies directly to the given information. V = IR R = V I Note that the voltage is not equal to the supplied EMF when the resistor is connected. 3) What is the internal resistance r of the battery? Internal resistance of a battery is similar to having two resistors in series. Thus, the equivalent resistance of the circuit is simply R tot = r + R From V = IR , R tot = r + R = V E I Thus, the internal resistance is r = V E I - R This time the total voltage supplied by the EMF is used since we are taking into account that there is internal resistance. In the previous problem, we used the remaining voltage available after the voltage drop across the internal resistor. 4) The picture shows a battery connected to two cylindrical resistors in parallel. Both resistors are made of the same material and are of the same length, but the diameter of resistor A is twice the diameter of resistor B. (For each statement select T True, F False). QUESTION: A) The resistance of wire B is four times as large as the resistance of wire A. B) The current through the battery is ﬁve times larger than the current through wire B. C) The power dissipated in wire A is 16 times the power dissipated in wire B. D) The resistance of wire B is twice as large as the resistance of wire A. E) The voltage drop across wire B is larger than the voltage drop across wire A.
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capa07 - Solution Derivations for Capa#7 1 Consider the...

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