Exercise Problem Correct. Correct. Heimadæmi 5. Part A. Part B. Due: 11:45pm on Thursday, February 18, 2016

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1 Heimadæmi 5 Due: 11:45pm on Thursday, February 18, 2016 You will receive no credit for items you complete after the assignment is due. Grading Policy Exercise In the circuit shown in the figure. the 6.0 resistor is consuming energy at a rate of 22.0 J/s when the current through it flows as shown. Ω Find the current through the ammeter. I = What are the polarity and emf of the battery, assuming it has negligible internal resistance? E E = 41.9 Problem You set up the circuit shown in, where R = 276 Ω. You close the switch at time t = 0 and measure the magnitude i of the current in the resistor R as a function of time t since the switch was closed. Your results are shown in, where you have chosen to plot as a function of t. ln i

2 Select the correct explanation of why your data points lie close to a straight line. The current in the circuit is i = Q 0 ln(i) = ln( ). Taking logs of the equation for gives i t. graph of versus will be a straight with slope equal to. ln(i) t The current in the circuit is. Taking logs of the equation for gives. i = Q 0 e t/ t i ln(i) = graph of ln(i) versus t will be a straight with slope equal to 1. The current in the circuit is. Taking logs of the equation for gives. i = Q 0 e t/ t i ln(i) = graph of ln(i) versus t will be a straight with slope equal to 1. The current in the circuit is i = Q 0 ln(i) = ln( ) e t/ e t/. Taking logs of the equation for gives i t. graph of versus will be a straight with slope equal to. ln(i) t 1 1 Use the graph in to calculate the capacitance C. Express your answer to two significant figures and include the appropriate units.

3 C = 5.4 μf Part C Use the graph in to calculate the initial charge Q 0 capacitor. on the Express your answer to two significant figures and include the appropriate units. = 200 μc Part D When i = , what is the charge on the capacitor? Express your answer to two significant figures and include the appropriate units. Q = 120 μc

4 Part E q 4 C When = , what is the current in the resistor? Express your answer to two significant figures and include the appropriate units. I = Exercise In the circuit shown in the figure each capacitor initially has a charge of magnitude 3.60 on its plates. nc fter the switch is closed, what will be the current in the circuit at the instant that the capacitors have lost 80.0% of their initial stored energy? S I = 13.9 lternative Exercise W How many 90, 120 light bulbs can be connected to a 20, 120 circuit without tripping the circuit breaker? (Note: This description of a light bulb gives the power it dissipates when connected to the stated potential difference; that is, a 25, 120 light bulb dissipates 25 when connected to a 120 line.) W W

5 26 Problem The average bulk resistivity of the human body (apart from surface resistance of the skin) is about 5.0. The conducting path between the hands can be represented approximately as a cylinder 1.6 m long and 0.10 m in diameter. The skin resistance can be made negligible by soaking the hands in salt water. Ω m What is the resistance between the hands if the skin resistance is negligible? R = 1000 Ω What potential difference between the hands is needed for a lethal shock current of 100? (Note that your result shows that small potential differences produce dangerous currents when the skin is damp.) m = 100 Part C With the current in part (b), what power is dissipated in the body? P = 10 W Problem 25.54

6 m cm cm mm m 2.0 length of wire is made by welding the end of a 120 long silver wire to the end of an 80 long copper wire. Each piece of wire is 0.60 in diameter. The wire is at room temperature, so the resistivities are as given in Table potential difference of 9.0 is maintained between the ends of the 2.0 composite wire. What is the current in the copper section? I = 81 What is the current in the silver section? I = 81 Part C What is the magnitude of E in the copper? E = 4.9 m Part D What is the magnitude of E in the silver? E = 4.2 m

7 Part E What is the magnitude of the potential difference between the ends of the silver section of wire? = 5.1 Problem lightning bolt strikes one end of a steel lightning rod, producing a current burst that lasts for 69. The rod is 2.0 long and 2.4 in diameter, and its other end is connected to the ground by 33 of 7.9 mm diameter copper wire. m cm m μs Find the potential difference between the top of the steel rod and the lower end of the copper wire during the current burst. = 180 Find the total energy deposited in the rod and wire by the current burst. W = 190 J Exercise MΩ s capacitor is charged to a potential of 12.0 and is then connected to a voltmeter having an internal resistance of fter a time of 4.00 the voltmeter reads 3.0. What is the capacitance?

8 C = F What is the time constant of the circuit? τ = 2.89 s Exercise The heating element of an electric dryer is rated at 4.1 when connected to a 240 line. kw What is the current in the heating element? I = 17 Is 12 gauge wire large enough to supply this current? yes no Part C What is the resistance of the dryer's heating element at its operating temperature?

9 R = 14 Ω Part D t 11 cents per kwh, how much does it cost per hour to operate the dryer? 45 cents Conceptual Question galvanometer G has an internal resistance r g. n MMETER is constructed by incorporating the galvanometer and an additional resistance R s. Which one of the figures below is the most appropriate circuit diagram for the ammeter? Score Summary: Your score on this assignment is 99.1%. You received 10.9 out of a possible total of 11 points.

[1] (b) Fig. 1.1 shows a circuit consisting of a resistor and a capacitor of capacitance 4.5 μf. Fig. 1.1

1 (a) Define capacitance..... [1] (b) Fig. 1.1 shows a circuit consisting of a resistor and a capacitor of capacitance 4.5 μf. S 1 S 2 6.3 V 4.5 μf Fig. 1.1 Switch S 1 is closed and switch S 2 is left