MOPANI WEST DISTRICT

PRACTICAL TEST 02
TERM 3
PHYSICAL SCIENCES
GRADE 12

TITLE: INTERNAL RESISTANCE AND EMF OF BATTERY

SURNAME

FIRST NAME

SCHOOL

DATE

Duration : 1hour

Learner’s Marks:
50
INSTRUCTIONS AND INFORMATION

1. Write your name on the cover of this booklet.

2. Answer ALL the questions in the space for it.
3. You may use a non-programmable calculator.
4. You may use appropriate mathematical instruments.
5. Show ALL the formulas and substitutions in ALL calculations.
6. Where necessary, round off your final numerical answers to a minimum of TWO decimal
places.
7. Provide brief motivations, discussions, and so on, where necessary.

FORMULAS

V=IxR Ԑ = I (R + r)

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QUESTION 1 : Internal resistance of a battery [15]

Learners want to determine the internal resistance of a cell. They follow an excerpt
from the worksheet below:

WORKSHEET:
METHOD:
1. Measure the EMF of the cell.
2. Configure the circuit as shown in the diagram above.
3. Set the rheostat to any resistance.
4. Take the reading on the voltmeter and ammeter.
5. Repeat step four 5 (or more) times after changing the resistance provided by
the rheostat each time.
6. Tabulate the terminal potential difference (volts) and electric current
(amperes) obtained by the experiment.
PRECAUTION: Do not keep the switch on for too long.

1.1. Describe how you will measure the EMF of the cell by referring to the current
and the placement of the voltmeter. (2)

1.2. Explain why the switch should not be turned on for too long. (1)

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1.3. After using the data in the table, the following graph is obtained when you
draw the voltmeter readings opposite the ammeter readings.

V (V)

1 I (A)

1.3.1. From the graph determine the value of the EMF of the cell. (1)

1.3.2. Use the graph to determine the internal resistance of the cell. You may NOT
use the equation Ԑ = I (R + r). (4)

1.3.3. Calculate the resistance of the rheostat when the current was 1 A. You may (3)
use the equation Ԑ=I(R+r).

1.3.3. Calculate the Vlost (internal potential difference) of the current is 1A. (1)

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1.4. A 3Ω resistance is added to the rheostat in series and the experiment is
repeated as shown above. The voltmeter and ammeter remain in the same
position.

1.4.1. What will be the impact of this change on the y-intercept of the graph? Write (1)
down only MORE, LESS or THE SAME.

1.4.2. What will be the impact of this change on the internal potential difference? (1)
Write down only MORE, LESS or THE SAME.

1.4.3. What will be the influence of this change on the internal resistance of the (1)
cell? Write down only MORE, LESS or THE SAME.

[15]

QUESTION 2 : Internal resistance of a battery [20]

A group of learners do an experiment to identify the emk (ɛ) and internal

determine resistance (r) of a certain battery. They connect the battery to a rheostat (variable
resistance), a low-resistance ammeter and a high-resistance voltmeter. Part of the circuit
used for the experiment is shown below.

2.1. Write down Ohm's law in words. (2)

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2.2. Plot the above circuit diagram in the space below. Draw the ammeter and
voltmeter to indicate how they should be connected in the circuit to perform
the experiment (2)

2.3. The data obtained from the experiment are given in the table below. Draw a
graph showing the results, V (V) vs I (A), on the grid below. Clearly label all
axes. Also, draw in the line of best fit on the chart. Lengthen the line so that
it intersects with both axes. (8)

Table showing the results: Potential difference vs. current.

Potential difference (V in V) Current (I in A)

0.90 3.75
1.60 3.40
2.40 2.60
3.50 1.70
4.30 1.00
4.45 0.65

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2.4. Use the information on the graph to answer the following questions.

2.4.1. Write down the value of the emk (ɛ), in V, of the battery. (1)

2.4.2. Calculate the internal resistance of the battery. (4)

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2.4.3. Calculate Vlost (internal potential difference) if the current is 0.8 A. (3)

[20]

QUESTION 3 : Compare circuits [5]

In another experiment, learners want to measure the resistance, ammeter and voltmeter
readings of different circuits. They connect circuit 1 using identical resistors. The internal
resistance of the battery and the resistance of the battery connecting wires are negligible
and can be ignored. The same components are used to switch circuit 2; the ONLY difference
is the arrangement of the resistors. The reading on voltmeter V1 is 3 V.

Circuit 1 Circuit 2

3.1. Write down the value of the EMF (ɛ), in V, of the battery. ____________ (1)

3.2. Compare the reading on the ammeter of circuit 2 with that of circuit 1. Write
only GREATER THAN, SMALLER THAN or EQUAL TO. (1)

3.3. Compare the reading on V2 with that of V1. Just write down BIGGER
IF, SMALLER THAN or EQUAL TO. (1)

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 3.4. Compare the resistance of R1 with that of R2. Just write down
GREATER THAN, SMALLER THAN or EQUAL TO. (1)

3.5. Which circuit is a potential divider? ______________________ (1)

[5]

QUESTION 4 : Compare circuits [6]

The circuit diagram below is used to investigate the relationship between the current in and
the potential difference over resistance R .

The results obtained are used to plot the graph below.

I (A)
V (V)

For the investigation, write down the following:

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4. Independent variable (1
1. )

4. Dependent variable (1
2. )

4. Conclusion that can be deduced from the graph (1

3. )

4.4. Calculate the resistance of resistance R using the gradient of the graph . (3)

[6]

QUESTION 5 : Compare circuits [4]

Several possible options are presented as answers to the following questions. Select the
answer and write down only the letter (A – D) next to the question number below.

5.1. In the circuit diagram below, the internal resistance of the battery and the
resistance of the conductive wires are negligible. The emk of the battery is ε.

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 If switch S is closed, the reading on voltmeter V1 is equal to ε and the reading
1
on voltmeter V2 is ...
3
A 1
ε.
2
B 1
ε.
3
C 2
ε.
3
D ε.
(2)

5.1 _________________

5.2. Consider the circuit diagram below.

Which ONE of the following combinations correctly represents the change in

the readings on the ammeter and the voltmeter when switch S is closed?

AMMETER READING VOLTMETER READING

A Decreases Decreases

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 B Decreases Increases
C Increases Decreases
D Increases Increases (2)

5.2 __________________
[4]
GRAND TOTAL: [50]

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