ECE323 Basic Electronic Circuits Assignment 5

  1. I measured a capacitance of about 5 nF for a capacitor made up of two Aluminum foil sheets (11 inches by 11 inches square) with a food wrap dielectric (estimated relative dielectric constant of 2.5). Based on these measurements, calculate the approximate thickness of the dielectric layer (in mm).

  2. A voltage of 50 V appears across a 10-mF capacitor. Determine the magnitude the charge and the energy stored on the capacitor.

  3. Given two capacitors, one of 5 nF and the other 800 pF, Find the capacitance if the capacitors are connected in series (end-to-end) and if they are connected in parallel (side-by-side).

  4. Show that the units of RC are seconds, given that C = Q/V and R = V/I.

  5. Given the circuit below, with R=1500 W and C = 300 nF. Find the time constant t and the equation for the voltage across the capacitor as a function of time if the voltage input is 2 V for t < 0 and 6 V for t > 0. Plot the results for a time of at least five time constants.

  6. I measured the rise time as a function of the resistance in an RC circuit. The capacitor was nominally 0.2 mF and the signal generator panel says that the equivalent resistance of the device is 50 W. The results I found are shown in the following table.

    R (ohms)rise time
    1000460 ms
    2000870 ms
    30001.05 msec
    40001.75 msec

    Plot this data and fit a straight line to the plot. The slope should be the capacitance and the x-intercept should be the negative of the equivalent resistance of the signal generator. Find these values and compare them to the nominal values.

Maintained by John Loomis, last updated 13 February 2008