Scenario -

Capacitors are widely used in electronic circuits and the following tasks will familiarise students with their function, types and uses, as well as to calculating the values in some simple circuits.

Task 1 -

a. With the aid of diagrams describe the construction of the following types of capacitors. Your diagrams should clearly indicate the plates and dielectric material.

I. Variable air capacitors

II. Mica

III. Paper

IV. Ceramic

V. Plastic

VI. Electrolytic

b. For each of the above capacitors state at a typical range of capacitance values AND a common maximum working voltages.

c. Describe the function and the applications of capacitors.

Task 2 -

This is a practical task to be carried out to determine the relationship between the voltage and current for a charging and discharging a capacitor.

Construct the following circuit using the components supplied using Electronic Workbench:

a. i. Connect the circuit shown above for the following values: C = 470μF, R = 500 kΩ

ii. Construct a table (like the one below) and record your results:

Table for Charging

iii. Measure the voltage across the capacitor at equal time intervals (say 5 seconds). You must take readings up to at least 5 times the time constant for the circuit.

iv. Repeat the above process measuring the voltage across the resistor.

Note: If you use a spreadsheet program, you can let It plot the graph that will be needed in later steps.

v. Discharge the capacitor through the resistor and measure the voltage across the capacitor taking readings every 5 seconds. You must take readings up to at least 5 times the time constant for the circuit.

vi. Record your results.

Table for Discharging

b. Repeat the steps (i) to (vi) again with the new value of C = 220 μF, keeping R = 500kΩ

From your results plot graphs, Use the vertical axis to show voltage and current and the horizontal axis for time.

Using the information from the graphs:

vii. State the relationship between voltage and current when a capacitor is charging.

viii. State the relationship between voltage and current when a capacitor is discharging.

Task 3 -

a. For circuit 1, calculate:

i. The total capacitance

ii. The total charge

iii. The charge on each capacitor

iv. The voltage across each capacitor

v. The energy stored in the circuit

Capacitors = 10μF, 15μF and 20 μF and the voltage is 12Vdc.

b. For circuit 2 calculate:

i. The total capacitance

ii. The total charge

iii. The charge on each capacitor

iv. The voltage across each capacitor

v. The energy stored in the circuit

Capacitors = 10μF, 15μF, and 20μF and the voltage is 12Vdc.

Task 4 -

For the circuit shown, calculate:

i. The equivalent capacitance of the network

ii. The voltage across each capacitor

iii. The charge on each capacitor

iv. The energy stored in the circuit

If the supply voltage is 25 V dc and each capacitor is 47μF.