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
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Time
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VCapacitor
|
VResistor
|
|
0 Seconds
|
0 V
|
?
|
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5 Seconds
|
?
|
?
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10 seconds
|
?
|
?
|
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...
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?
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|
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...
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|
|
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...
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|
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?
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?
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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
|
Time
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VCapacitor
|
VResistor
|
|
0 Seconds
|
Max v ?
|
?
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5 Seconds
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less ?
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?
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10 seconds
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Less ?
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?
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...
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?
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...
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?
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...
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?
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?
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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.
