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14.2 The Flow of Electric Charge How much charge moves when current flows? 1 Measuring voltage Table 1: Capacitor discharge data Time (s) 0 2 a. Voltage (V) Time (s) 70 10 80 20 90 30 100 40 110 50 120 60 130 Voltage (V) How much current flowed? Use Ohm’s law to write down a formula for the current flowing through an electrical device if you know the voltage and the resistance. Investigation 14.2 The Flow of Electric Charge Page 1 of 4 b. Use the relationship you found in question 2a to fill in Table 2 by calculating how much current was flowing through the resistor. Table 2: Capacitor discharge data Time (s) Current (A) 0 10 20 30 40 50 60 3 a. Time (s) Current (A) 70 80 90 100 110 120 130 Thinking about what you observed Make a graph of the current versus time for the capacitor. Draw a smooth curve through the points on your graph. Investigation 14.2 The Flow of Electric Charge Page 2 of 4 b. Describe what your graph shows about the current over time. Explain the reason for the current to change in this way. c. Suppose a light bulb had been used instead of a resistor. What would you have noticed about the light bulb as time went on? Why? d. Calculate the power of the resistor at a time of 10 seconds and at a time of 60 seconds. Do your answers support your explanation in question 3c? 4 a. Calculating charge from your graph Write down a formula that allows you to calculate charge if you know the current and the time. b. If current is in amperes and time is in seconds, what is the unit of charge represented by your formula from question 4a? c. Look at the scale on your graph and determine the time and current represented by one block. Draw one graph block and label its dimensions. Investigation 14.2 The Flow of Electric Charge Page 3 of 4 d. Use your answers to questions 4a and 4b to calculate the amount of charge represented by one block on your graph. Show your work. 19 20 1 21 2 6 3 7 10 4 8 11 13 15 5 9 12 14 16 17 18 22 23 24 Count the total number of grid blocks under the curve. Add partial blocks together to make whole blocks. e. Count the number of blocks between the curved line on your graph and the x-axis as shown above. Include fractions of blocks in your count, and estimate as accurately as you can. f. In question 4d you figured out the amount of charge represented by one block. Use this information and the number of total blocks under your graph to calculate the total charge that flowed from the capacitor and through the circuit. g. One coulomb is equal to 6.24151 × 1018 electrons. Calculate the number of electrons that flowed from the capacitor. h. Explain how the results for your investigation would differ if you used a 30 resistor instead of a 20 resistor. If you have time you may want to try the experiment with a resistance of 30 (20 and 10 resistors in series) to see if you are correct. Investigation 14.2 The Flow of Electric Charge Page 4 of 4