Herefordshire College of Technology
Center Number 024150
Student:
Course: : BTEC Level 3 Subsidiary
Diploma in Engineering / Diploma in
Electrical/Electronic Engineering
Unit/s: 6 – Electrical & Electronic Principles
Outcome/s: 2 - Capacitance
Grading criteria:
P5 Carry out an experiment to determine the relationship between the voltage and
current for a charging and discharging capacitor.
Pass:
Merit:
Distinction:
Instructions:
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All work is to be your own.
Attempt all questions.
Work to be legible and succinct, with an adequate grasp of grammar,
punctuation and spelling.
Calculators may be used but show working step by step.
Ensure sketches & diagrams are clear, accurate & labelled.
True graphs, titled & axes labelled.
List sources where appropriate.
Student feedback:
Student declaration – The assignment attached is my own work.
Signed:
Date:
Assessor feedback:
Signed:
Date:
Internal verification
(Before issue)
CRT
Issue date
Student hand in date
Internal verification
(assessment decision)
10/11/10
TUTOR R.A.KERSHAW.
Unit 6: Electrical & Electronic Principles
Assignment - Capacitors - Practical
Page 1 of 6
HCT. BTEC. Assessment
Center Number 024150
Grading Criteria and Feedback
P5 Carry out an experiment to determine the relationship between the
voltage and current for a charging and discharging capacitor.
Unit 6: Electrical & Electronic Principles
Assignment - Capacitors - Practical
Page 2 of 6
HCT. BTEC. Assessment
Center Number 024150
Capacitance Charging and Discharging Practical Task
Objective
To investigate the charge and discharge of a capacitor.
Components and test equipment
Breadboard, 9 V DC power source (a DC power supply with an output of 9 V at up
to 400 mA), 2 digital multimeters with test leads, resistors of 100, 220 and 47
kΩ, capacitor of 1,000 µF, insulated wire links (various lengths), assorted
crocodile leads. A watch or clock with a seconds display will also be required for
timing.
Procedure
(a) Charging circuit
Connect the charging circuit with R = 100 kΩ and C = 1,000 µF, as shown below:
A
Place a temporary shorting link across the capacitor. Set the voltage meter to
the 20 V DC range, the ammeter to a suitable DC current range and remove the
shorting link. Measure and record the capacitor voltage and current at 25 s
intervals over the range 0 – 250 s after removing the shorting link. Record your
result in the table shown below. Repeat with R = 220 kΩ and R = 47 kΩ.
Charging circuit with R = 100 kΩ, C = 1,000 µF
Time (s)
Voltage (V)
Current (µA)
0
25
50
75
100
125
150
175
200
225
250
125
150
175
200
225
250
Charging circuit with R = 220 kΩ, C = 1,000 µF
Time (s)
Voltage (V)
Current (µA)
0
25
50
75
100
Unit 6: Electrical & Electronic Principles
Assignment - Capacitors - Practical
Page 3 of 6
HCT. BTEC. Assessment
Center Number 024150
Charging circuit with R = 47 kΩ, C = 1,000 µF
Time (s)
Voltage (V)
Current (µA)
0
25
50
75
100
125
150
175
200
225
250
(b) Discharging circuit
Connect the discharging circuit with R = 100 kΩ and C = 1,000 µF, as shown
below:
A
Leave the link in place for a few seconds after the supply voltage has been
switched on, and then remove the link. Measure and record the capacitor
voltage and current at 25 s intervals over the range 0–250 s from removing the
link. Record your result in a table showing capacitor voltage against time.
Repeat with R = 220 kΩ and R = 47 kΩ.
Discharging circuit with R = 100 kΩ, C = 1,000 µF
Time (s)
Voltage (V)
Current (µA)
0
25
50
75
100
125
150
175
200
225
250
150
175
200
225
250
150
175
200
225
250
Discharging circuit with R = 220 kΩ, C = 1,000 µF
Time (s)
Voltage (V)
Current (µA)
0
25
50
75
100
125
Discharging circuit with R = 47 kΩ, C = 1,000 ΩF
Time (s)
Voltage (V)
Current (µA)
0
25
50
75
100
Unit 6: Electrical & Electronic Principles
Assignment - Capacitors - Practical
125
Page 4 of 6
HCT. BTEC. Assessment
Center Number 024150
Graphs and calculations
Use the graph sheets to plot graphs of voltage and current (on the vertical axis)
against time (on the horizontal axis) for both the charging and discharging
circuits (and for each C–R combination).
Calculate the time constant for each combination of resistance and capacitance
that you used in the investigation.
Time Constant Calculations
R = 100 kΩ, C = 1,000 µF
R = 220 kΩ, C = 1,000 µF
R = 47 kΩ, C = 1,000 µF
Conclusion
Comment on the shape of the graphs. Is this what you would expect? For each
combination of resistance and capacitance, estimate the time constant from the
graph. Compare these values with the calculated values. If they are not the
same suggest possible reasons for the difference.
Comments
Unit 6: Electrical & Electronic Principles
Assignment - Capacitors - Practical
Page 5 of 6
HCT. BTEC. Assessment
Center Number 024150
Capacitor current (µA)
Graphs of voltage plotted against time for the charging circuit
Capacitor current (µA)
Graphs of voltage plotted against time for the discharging circuit
Unit 6: Electrical & Electronic Principles
Assignment - Capacitors - Practical
Page 6 of 6