Report Sheet Lab 9 RC Circuits Lab - Answers

12. What is the function of a capacitor in a circuit? How does it affect the amount of charge that flows? How does it affect the rate at which charge flows? How does it affect the initial and final voltage across the resistor? How does the capacitor make charge move when there is no battery in the circuit? The capacitor stores electrical energy as charge. It affects the amount of charge that flows by storing it during charging. It influences the rate of charge/discharge, affecting the time constant. It affects the initial and final voltage across the resistor by controlling the charging and discharging rates. In the absence of a battery, a charged capacitor acts as a temporary voltage source, making the charge move in the circuit during discharge. PART 2. CALCULATING THE TIME CONSTANT OF RC CIRCUIT. 1. Change the values on the capacitor and the resistor. Select R = 100.00 Ω, and C = 0.10 F and charge the capacitor. How long it takes to fully charge the capacitor? Is charging linear? The time constant of RC circuit is given by T=RC T=100*0.1=10s After a time of 5T the capacitor is now fully charged. So, the time taken to fully charge is 50s. No, the charging is not linear and is given by [1-exp(-t/T)] 2. Follow the steps in the Procedure and complete Table 1 below: Table 1. V(V) t 1 (s) t 2 (s) t 3 (s) ´ t (s) ln ( ɛ /V) 8 7 6 5 4 3 2 1 ɛ = R = C = Calculated (theoretical) RC = Slope = RC from the graph (experimental) = Calculations 1. Calculate the average times ´ t and record them in the table. 2. Calculate the values of ln ( ɛ /V) and record them in the table. 3. Perform a linear least squares fit of the data with ln ( ɛ /V) as the vertical axis and ´ t as the horizontal axis. 4. Record the value of the slope. 5. Calculate RC as the reciprocal of the slope and record it.