Herefordshire College of Technology Center Number 024150 Course: : BTEC Level 3 Subsidiary Diploma in Engineering / Diploma in Electrical/Electronic Engineering Student: 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: 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: Internal verification (Before issue) CRT 10/11/10 Date: Issue date Student hand in date Internal verification (assessment decision) TUTOR R.A.KERSHAW. Unit 6: Electrical & Electronic Principles Page 1 of 6
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 Page 2 of 6
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 Charging circuit with R = 220 kω, C = 1,000 µf Unit 6: Electrical & Electronic Principles Page 3 of 6
Charging circuit with R = 47 kω, C = 1,000 µf (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 Discharging circuit with R = 220 kω, C = 1,000 µf Discharging circuit with R = 47 kω, C = 1,000 ΩF Unit 6: Electrical & Electronic Principles Page 4 of 6
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 Page 5 of 6
Graphs of voltage plotted against time for the charging circuit Graphs of voltage plotted against time for the discharging circuit Capacitor current (µa) Capacitor current (µa) Unit 6: Electrical & Electronic Principles Page 6 of 6