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Chapter
13
Circuit analysis
Investigation 13.1
Series circuits
➤ Page 334
Aims
• To investigate the current at points around a circuit
that has two resistors connected in series
• To compare the voltage drops around a series circuit
with the emf of the voltage supply
• To compare the total resistance of a series circuit with
the values of the individual resistors in the circuit
Equipment
•
•
•
•
•
•
a variable power supply
2 fixed resistors of different sizes
an ammeter
a voltmeter
a switch
connecting wires
Suggested answers to questions
3. There may have been parallax errors in reading the
voltmeter and the ammeter. Poor connections in the
circuit will produce extra resistance. The ammeter
and voltmeter have a small influence on the circuit.
Handy hint
Make sure the students have the voltmeter and ammeter
correctly connected before closing the switch.
Investigation 13.2
Parallel circuits
➤ Page 334
Aims
Handy hint
Make sure the students have the voltmeter and ammeter
correctly connected before closing the switch.
Investigation 13.3
Determining the emf and
internal resistance of two
dry cells, one old and one new
➤ Page 338
Aim To determine the emf and internal resistance of
two dry cells, one old and one new
Equipment
•
•
•
•
two dry cells, one old, one new
a high-resistance voltmeter
an ammeter
resistors with values 2 Ω, 5 Ω, 10 Ω and one with a
much larger value, at least 100 Ω. (Any carbon or
metal film resistor could be used.)
• connecting wires
• switch
Suggested answers to questions
4. The highest recorded voltage is an indication of the
emf of the cell.
6. In the second arrangement the voltmeter would give
the emf of the cell when the switch was open. Readings with the switch closed should be the same as in
the original arrangement if the ammeter has negligible resistance.
7. As a dry cell gets older, the emf remains constant, but
the internal resistance increases.
Handy hint
Make sure one of the dry cells is ‘flat’ before starting the
experiment.
• To investigate the flow of current in a parallel circuit
• To investigate the voltage drops in a parallel circuit
• To calculate the effective resistance of two resistors in
parallel
• To verify that for two resistors in parallel
1
1
1
----- = ----- + ----R1
R2
RT
Equipment
•
•
•
•
•
•
a variable power supply
2 fixed resistors of different sizes
an ammeter
a voltmeter
a switch
connecting wires
jp12ech13-circuit.pdf
© John Wiley & Sons Australia, Ltd 2004