Physical Sciences
Prescribed Experiment for formal Assessment
Knowledge Area: Electricity and Magnetism
Topic: Internal resistance and Series-Parallel networks
Part 1
Aim
To determine the internal resistance of a battery
Precautions
Do not leave the switch closed at all times. The battery will run flat. Close the switch only
for taking the readings on the voltmeter and Ammeter. Take your readings accurately. Do
not conduct the experiment with wet hands.
Instructions
Place 4 x 1,5V cells in a cell holder in a series connection. Connect a Switch, Ammeter and a
Rheostat in series to the battery. Connect the Voltmeter across the battery.
If a rheostat is not available, resistors or bulbs could be used in the place of a rheostat. The
resistors or bulbs must be connected in series. One resistor/bulb must be connected first and then
the resistors/bulbs be increased to two in series, three in series, etc.
Draw the electrical circuit diagram. Set the Rheostat at 10. Close the switch and reduce the
resistance in the Rheostat step by step, increasing the current at the same time. Take the
ammeter and voltmeter readings in each case/step. Open the switch while recording the readings
in order to spare the batteries’ life span.
Take and record a minimum of 5 readings. Interpret and analyse the data in order to determine the
internal resistance. Write a conclusion and prepare a report (write-up).
Part 2
Aim:
1. To determine the equivalent resistance in a Series-parallel network electrical circuit.
2. To compare the experimental values of the equivalent resistance to the theoretical values.
Instructions:
Place 4 x 1.5V cells in a cell in a cell holder in a series connection. Connect a voltmeter (V1)
across the battery. Connect three resistors of different resistance. One resistor must be connected
in series with a voltmeter (V2) across and the other two resistors must be connected in parallel
with a voltmeter across (V3). Connect a switch and an ammeter.
1
Draw the electrical circuit. Determine the equivalent resistance experimentally and compare the
readings to the calculated values of equivalent resistance. Submit a report (write up)
Part 1 Possible Marking Memorandum and Rubric
Internal resistance
Topic: Internal resistance and Series-parallel networks.
Aim: To determine the internal resistance of a battery.
Apparatus:
 4 (Size RD) 1.5V cells 
 Voltmeter
 Ammeter
 10 Rheostat or Resistors or Bulbs
 Connecting wires
 Cell holder
 Switch
Precautions:
Do not leave the switch closed at all times. The battery will run flat. Close the switch only for
taking the readings on the voltmeter and Ammeter. Take your readings accurately
Method:
STEP
Procedure
1
4 cells, 1,5V each were placed in a cell holder and connected in series. 
2
A switch was connected to the positive terminal of the battery. 
3
The negative terminal of the ammeter was connected to the one end of the switch.
(2)
(7)
(1)
(1)
(1)

4
5
6
A rheostat was set at 10 and its negative terminal was connected to the positive (2)
terminal of the ammeter. Its positive terminal was connected to the negative terminal
of the battery. 
(1)
A voltmeter was connected in parallel across the battery
Electrical circuit:
(5)
Allocate one mark for each

component of electrical the
V
circuit drawn and

connected correctly.
r

A


That is: The voltmeter,
Ammeter, Rheostat, switch
and the battery with
internal resistor.
NB: Resistors/ bulbs connected in series could be used in the place of a rheostat,
starting with one bulb/resistor and increasing the resistance after taking and
recording the readings
2
7
8
9
The switch was closed. The ammeter and the volmeter readings were taken and (1)
recorded when the rheostat was set at 10.
The resistance in the rheostat was reduced five times and each case a volmeter and (2)
the ammeter readings were taken and recorded.
The switch was closed to take the readings and it was opened immediately after (1)
taking the readings. 
3
Results:
(NB: the results below are hypothetical and illustrative. The learners must be assessed on
their recorded results accordint to the experiment conducted.)
1.
Tabulating results
(3)

I (A)
VT(V)
2. Labelling Columns (Quantity with units)
0
6
0.6
5.76
3. Correct Experimental values
1.2
5.52
1.8
5.28
2.4
5.04
Interpretation and analysis:

Graph
1. Suitable caption
2. Labelled axis
(7)
3. Calibration on the axis
4. Shape of the graph
Gradient is the internal resistance and therefore:
Conclusion:
 The y-intercept of the graph is the EMF.
 The x-intercept of the graph is the maximum electrical current (I).
 The gradient or slope of the graph is the internal resistance (r) = 0,42
Grand total
(1)
35
4
Part 2 Possible Marking Memorandum and Rubric
Equivalent resistance
Comparing experimental equivalent resistance values to theoretical values
Topic: Equivalent resistance in series-parallel circuits
Aim: To determine the equivalent resistance in series-parallel electrical circuits
To compare experimental values of the equivalent resistance to theoretical values.
Apparatus:
 4(RD) 1,5V cells
 Cell holder
 Switch
 3 Voltmeters
 Ammeter
 3 resisters (different sizes)
 Connecters
Precautions:
Do not conduct the experiment with wet hands. Ensure that the ammeter and the voltmeter are
connected together. If the bulbs are used in place of resistors, the current (amperes) and the
voltage labelled on the bulbs should be taken into account.
Method
STEPS
PROCEDURE
1
4 cells (1,5V each) were placed in a cell holder and were connected in series.  (1)
2
(1)
The switch was connected to the positive side of the battery.
3
(1)
The negative terminal of the ammeter was connected to the switch in series. 
4
(1)
One resistor was connected to the positive terminal of the ammeter in series.
5
Two resistors were connected in parallel and connected to the other resistor.  (1)
6
Volmeters, V1, V2 and V3 were connected across the battery, a resistor in series (1)
and the parallel combination of resistors, respectively. 
7
(9)

V1
Allocate one mark for each
component of electrical the
circuit drawn and
connected correctly.

r

A


R1


R2
R3

V2
That is: Each voltmeter,
Ammeter, each external
resistor, switch and the
battery with internal
resistor.
V3

5
8
The switch was closed, the reading on the ammeter and the voltmeters were
taken and recorded. 
Results: NB: The values are hypothetical
EMF (V1)
Terminal
voltage (V1)
V2
V3
I
(1)
Internal
resistance
6V
6