Passage III

An electrical circuit contained a 12-volt (V) battery, a resistor (a device that resists the flow of electricity), a capacitor (a device that stores electrical charge and electrical energy), a voltmeter (an instrument for measuring voltage), and a switch, as shown in Figure 1.

Some students studied the behavior of the circuit.

Experiment 1

The students used a 1 × 107 ohm (Ω) resistor and a capacitor with a capacitance of 1 × 10–6 farad (F). (Capacitance is a measure of the maximum amount of electrical charge and electrical energy a capacitor can store.) The capacitor was initially uncharged. At time zero, the students simultaneously closed the switch and started a stopwatch. At time zero and at 12 sec intervals thereafter, they recorded the voltage across the capacitor. Their results are shown in Table 1.

Experiment 2

Using the 1 × 107 Ω resistor and several different capacitors, the students determined the length of time from when the switch was closed until the voltage across the capacitor reached 6 V. Their results are shown in Table 2.

Experiment 3

The students conducted the same procedure described in Experiment 2, except that they used a constant capacitance of 1 × 10–6 F and several different resistors. Their results are shown in Table 3.

14. In Experiment 1, the time constant of the circuit was the time required for the voltage across the capacitor to reach approximately 7.6 V. The time constant of the circuit used in Experiment 1 was:

Answer and Explanation

Your Answer is

Correct Answer is F

Explanation

Look at table 1. As the time increases, the Voltage also increases. When the time is 12 sec, the voltage is 8.4 V, which is already greater than the 7.6 V mentioned in the question stem, so the time constant should be less than 12 sec