Download STUDENT COPY Capacitor Student Copy

SHORT EXPERIMENTAL INVESTIGATIONS 1
EXPERIMENT 1: Capacitor Investigation
Science Department
Subject Details
10 Physics
2
Subject:
Semester:
Unit:
Name:
Electronics
Year:
Teacher:
Item:
Mr Carson
SEI1
Conditions
You must adhere to the school assessment policy.
Formulae booklet will be supplied and calculators allowed.
Show all working, neatly and well set out, in the exam booklets provided
Criterion
Overall Grade
DATE SET:
Draft Due Date:
DUE DATE :
Knowledge and
Conceptual
Understanding
Investigative
Processes
Evaluating and
Concluding
Criterion
A
B
C
D
E
Knowledge and
conceptual
understanding
The student work has the following
characteristics:
The student work has the following
characteristics:
The student work has the following
characteristics:
The student work has the
following characteristics:
reproduction and interpretation of
complex and challenging
concepts, theories and principles
reproduction and interpretation of
complex or challenging concepts,
theories and principles
reproduction of concepts, theories
and principles
reproduction of simple ideas
and concepts
The student work has
the following
characteristics:
comparison and explanation of
complex concepts, processes
and phenomena
comparison and explanation of
concepts, processes and
phenomena
explanation of simple processes
and phenomena
description of simple
processes and
phenomena
recognition of isolated
simple phenomena
linking and application of
algorithms, concepts, principles,
theories and schema to find
solutions in complex and
challenging situations.
linking and application of algorithms,
concepts, principles, theories and
schema to find solutions in
complex or challenging situations.
application of algorithms,
principles, theories and schema
to find solutions in simple
situations.
application of algorithms,
principles, theories and
schema.
application of simple
given algorithms.
The student work has the following
characteristics:
The student work has the following
characteristics:
The student work has the following
characteristics:
The student work has the
following characteristics:
 formulation of justified
significant questions/hypotheses
which inform effective and
efficient design, refinement and
management of investigations
 formulation of justified
questions/hypotheses which
inform design and management of
investigations
formulation of questions and
hypotheses to select and
manage investigations
implementation of given
investigations
The student work has
the following
characteristics:
assessment of risk, safe selection
and adaptation of equipment,
and appropriate application of
technology to gather, record and
process valid data
assessment of risk, safe selection of
equipment, and appropriate
application of technology to
gather, record and process data
assessment of risk, safe selection
of equipment, and appropriate
application of technology to
gather and record data
safe use of equipment and
technology to gather and
record data
safe directed use of
equipment to gather
data
systematic analysis of primary and
secondary data to identify
relationships between patterns,
trends, errors and anomalies.
analysis of primary and secondary
data to identify patterns, trends,
errors and anomalies.
analysis of primary and secondary
data to identify obvious patterns,
trends, errors and anomalies.
identification of obvious
patterns and errors.
recording of data.
The student work has the following
characteristics:
The student work has the following
characteristics:
The student work has the following
characteristics:
The student work has the
following characteristics:
 analysis and evaluation of
complex scientific
interrelationships
 analysis of complex scientific
interrelationships
 description of scientific
interrelationships
 identification of simple
scientific interrelationships
The student work has
the following
characteristics:
 exploration of scenarios and
possible outcomes with
justification of conclusions/
recommendations
 explanation of scenarios and
possible outcomes with discussion
of conclusions/ recommendations
 description of scenarios and
possible outcomes with
statements of conclusion/
recommendation
 identification of scenarios
or possible outcomes
 statements about
outcomes
 discriminating selection, use
and presentation of scientific
data and ideas to make
meaning accessible to intended
audiences through innovative
use of range of formats.
 selection, use and presentation of
scientific data and ideas to make
meaning accessible to intended
audiences in range of formats.
 selection, use and presentation
of scientific data and ideas to
make meaning accessible in
range of formats.
 presentation of scientific
data or ideas in range of
formats.
 presentation of
scientific data or
ideas.
Investigative
processes
Evaluating and
concluding
reproduction of isolated
facts
guided use of given
procedures
 identification of
obvious scientific
interrelationships
Writing your Report
Once you have collected your data and analysed it, you can begin to compile your report. The outline and checklist for
each of these sections is provided.
SECTION
Outline of Section
TITLE
An accurate, concise description of the
project, which provides the reader with an idea
of what the investigation is about
CONTENTS
A single page listing the contents of the report,
and what page each section is on. A Table of
Diagrams may also be relevant.
THEORY
A theoretical and descriptive introduction to
the project. It should outline the theoretical
background of the project
METHOD
An accurate description of materials used and
experimental procedures, allowing the
investigation to be repeated
RESULTS
A full description of all data, with use of tables
and figures to summarise and present findings
ANALYSIS
The place to describe the relevance of your
results and any limitations in your approach
i.e. Providing the reader with an interpretation
of both qualitative and quantitative data
CONCLUSION
A summary of your analysis. What are the
key points that can be drawn from the results
and analysis
BIBLIOGRAPHY
An alphabetical list of all sources used during
the project.
Student Activity
28
Charge and time constant of capacitors
TASK
To investigate some properties of a capacitor, including charge and discharge characteristics and the time constant of an
R–C circuit.
THEORY
A capacitor is a device that stores charge. The total charge on a capacitor is normally zero—there being equal positive
and negative charge on the respective plates. The charge on a capacitor is the amount of charge that flows onto one plate
(of the capacitor) and will be equal to the amount that flowed off the other plate. The capacitor will be charged to +Q on
one plate and –Q on the other.
The amount of charge on the plates depends directly on the voltage across the capacitor: C = Q/V or Q = CV, where Q is
in coulombs; C, in farads; and V, in volts. As 1 coulomb is a huge amount of charge, normal capacitors are rated in
smaller units, such as microfarad (F).
The rate at which a capacitor charges or discharges within a circuit is the key to many important electronic circuits.
The time that a capacitor takes to discharge or charge depends on both the capacitance and the resistance in the circuit.
The time constant  = RC, where R is the resistance (in ohms) and represents the time (in seconds) for the capacitor to
reach 63% of its full charge.
EQUIPMENT
•
•
•
•
•
AC/DC power supply
multimeter
Labquest
470, 3300 F electrolytic capacitor
10 k resistor(if using 3300μF) and 100kΩ (if using
470μF)
• connecting wires
• circuit ‘breadboard’
• 6V battery
WARNING: An electrolytic capacitor could explode if it is connected incorrectly. Check your circuits with
your teacher.
NOTES ON METHOD
Part I: Charging and discharging a capacitor
1. Using a multimeter, measure and record the voltage of the battery. Connect up the circuit shown below. Make sure
the electrolytic capacitor is the correct way around. The positive lead must be connected to the positive terminal of
the power supply. An electrolytic capacitor could explode if it is connected incorrectly. (Non-electrolytic capacitors
can be connected either way.) DO NOT SWITCH ON YET! Put the data logger where the voltmeter would go –
red lead on positive.
continued
2. The circuit you have constructed is set up so that the data logger monitors the voltage across the 10 k resistor and
therefore the current charging the capacitor. Check that the data logger is connected properly and switched on. By
observing the changing voltage, describe how the current changes during the charging process.
ICT
A voltage sensor and graphing software will give an immediate graph of the change in voltage. Keep your
sampling rate at a minimum of 20 samples per second to enable changes to be clearly observed. Higher samples
rates will increase the resolution of small changes at the expense of larger data tables.
3. Disconnect the leads from the battery. Set the data logger up for another run. Press the record button on the data
logger and another person in your group immediately connects the two leads, that had been connected to the battery,
together.
Part II: Capacitors with AC and DC voltages
4. Connect the circuit shown in the diagram below. A battery must be used. Leave the battery disconnected initially.
ICT
Use the same settings as for Part A of this activity. There is no need for separate settings for AC/DC voltage as
described for voltmeters.
5. Connect the battery and immediately measure the voltage across the resistor with the multimeter switched to the DC
range. Record this voltage.
6. Leave the circuit connected for about one minute. Is there any DC flowing in the circuit one minute after the circuit
has been switched on? Record the corresponding voltage.
7. Replace the 6 V battery with a 6 V AC supply. With the multimeter switched to the AC ranges, measure the voltage
across the resistor. Record this voltage.
8. Leave the circuit connected for about one minute. Is there any current flowing in the circuit one minute after the
circuit has been switched on? Record the corresponding voltage.
9. Explain any differences in what you observed when AC or DC flow through capacitors.
DATA & ANALYSIS
• Initial DC voltage: ……………… V
• Final DC voltage: ……………… V
• Initial AC voltage: ……………… V
• Final AC voltage: ……………… V
Heinemann Queensland Science Project—Physics TRAD ISBN: 978 1 74081 872 8
Copyright © Pearson Education Australia (a division of Pearson Australia Group Pty Ltd)
28
Charge and time constant of capacitors
Part III: Measuring the time constant
Note: This section uses a CRO or voltage sensor. If you will be using a CRO, check with your teacher and ensure you
are familiar with key features before continuing.
ICT
Use the same sampling rate as per previous sections. Display a graph of voltage against time. Disregard all steps
regarding CRO set-up in the following method.
10. Adjust the time base of the CRO to obtain a straight-line trace with the 0 V line shifted downwards so that a 6 V
deflection may be observed on the screen without adjustment.
11. Connect the circuit shown, making sure that the capacitor is connected the correct way around. The clip-lead must be
in place as shown.
12. Using a stopwatch, remove the clip-lead and record the time taken for the capacitor to charge from 0 V to 6 V.
ICT
Time is measured automatically. Observe the shape of the graph as it is drawn.
13. If measuring manually, you have probably found this extremely difficult to measure. Try estimating the time constant
instead—that is, the time it took for the capacitor to become about two-thirds charged. To do this, discharge the
capacitor and measure how long it takes for the voltage to drop by about 4 V.
14. If time permits, change the combination of resistor and capacitor. Repeat steps 1–4 for each combination.
15. Comment on any discrepancies between the experimental and theoretical values of the time constant. (Remember that
resistors have tolerance levels and that the tolerance levels of capacitors are usually between –20% and +50%.)
16. If you assume that the time base measurements that you did were correct, use your results for the 100 µF capacitor to
find the actual value of its capacitance (assume the quoted resistor value is correct). Use t = CR.
DATA & ANALYSIS
• Time taken to 6 V: ……………… s
• Time taken to 4 V: ……………… s
• Value of capacitance from measured time constant: ……………… F
CONCLUSIONS
Summarise your results for the measured time constant and hence state the value of the capacitance. Compare this with
the stated value.
Heinemann Queensland Science Project—Physics TRAD ISBN: 978 1 74081 872 8
Copyright © Pearson Education Australia (a division of Pearson Australia Group Pty Ltd)
28
Charge and time constant of capacitors
continued
QUESTIONS
1. Explain the characteristic shape of the graph of charge/discharge of a capacitor.
2. Was there any current flowing in the circuit one minute after the circuit was switched on when using the battery?
Explain.
3. Was there any current flowing in the circuit one minute after the circuit was switched on when using the AC supply?
Explain.
4. Why is it so difficult to manually measure the time taken for the capacitor to be fully charged?
5. (ICT users only) How does the time taken to fully charge the capacitor compare with the time constant? Estimate the
comparison from the graph of voltage against time. Explain how you determined the point at which the capacitor was
fully charged.
Heinemann Queensland Science Project—Physics TRAD ISBN: 978 1 74081 872 8
Copyright © Pearson Education Australia (a division of Pearson Australia Group Pty Ltd)