ITEC1010 – Section M – Winter 2000

Practice Spreadsheet Problem

Capacitor Charging

Design and implement an Excel spreadsheet to model a capacitor charging from an applied voltage. Figure 1 illustrates a representative circuit.

Figure 1. Representative circuit for a capacitor charging

In the figure, the capacitor, C, is in series with a resistor, R. The input voltage, V_i, is applied to the RC combination when the switch closes.

The voltage across the capacitor is given by V_c. Assuming an initial discharged state, the capacitor charges following switch closure according to the formula in Figure 2.

Figure 2. Formula for a capacitor charging

In the formula, R is the resistance in Ohms (W), C is the capacitance in Farads (F), t is the time following switch closure in seconds (s), and V_i is the input voltage in Volts (V). These are constants. Set them to nominal values of R = 15 kW, C = 15 mF, and V_i = 9 V. e is the base of the natural logarithm.

Design your spreadsheet to calculate and graph the progress of the capacitor charging over a period of 1 second using dt = 0.001 s. Hint: Use Excel’s EXP formula when working with exponents to the base e.