• Join over 1.2 million students every month
• Accelerate your learning by 29%
• Unlimited access from just £6.99 per month
Page
1. 1
1
2. 2
2
3. 3
3
4. 4
4
5. 5
5
6. 6
6
7. 7
7
8. 8
8
9. 9
9
10. 10
10
11. 11
11
12. 12
12

# Investigating Internal Resistance

Extracts from this document...

Introduction

Investigating the internal resistance of a specific lab power pack.

Luke Parker

Planning

Title:

Investigating the internal resistance of a specific lab power pack.

Aim:

To discover the internal resistance of a lab power pack as the EMF and current are altered.

Apparatus:

• Lab power pack
• Wires
• Variable resistor
• Voltmeter
• Ammeter
• Ruler
• Pencil

Diagram (fig.1)

Safety Precautions:

This experiment in general does not have many risks involved however safety precautions need to be taken. The experiment involves electricity; therefore water should be kept well clear. The power should only be supplied for the minimum time possible for results to be taken accurately. This is to prevent the apparatus getting hot and reduce time when the electrics are in use.

Variables:

The possible variables within this experiment are as follows:

• Voltage
• Current
• External resistance

These three will all be varied. The Voltage will be set at a specific setting on the power pack and not be altered until all voltage and current results are recorded for all resistance values. Then the voltage will be changed and once again the voltage and current values taken for each resistance level.

This means the results for each voltage setting will be compared making voltage a fixed variable for a certain set of results. However the voltage setting is changed to repeat the same experiment.

The main variable in this experiment is the external resistance.

Middle

0.07

0.07

R4

1.07

1.07

1.08

0.11

0.11

0.12

R5

1

0.99

1

0.3

0.3

0.31

4V Setting: Emf = 4.7V

 Resistance (Ohms) Voltage (V) Current (A) R1 4.36 4.36 4.35 0.165 0.17 0.16 R2 4.32 4.31 4.32 0.2 0.2 0.2 R3 4.27 4.26 4.26 0.28 0.28 0.28 R4 4.17 4.17 4.18 0.45 0.45 0.45 R5 3.77 3.77 3.76 0.85 0.9 0.9

6V Setting: Emf = 6.66V

 Resistance (Ohms) Voltage (V) Current (A) R1 6.16 6.17 6.16 0.235 0.24 0.24 R2 6.09 6.1 6.1 0.29 0.295 0.29 R3 5.98 5.98 5.99 0.4 0.4 0.4 R4 5.77 5.78 5.77 0.63 0.62 0.63 R5 5.32 5.32 5.31 1.1 1.1 1.1

Tables of averages must also be compiled as this allows voltage and current to be seen as one point and therefore more easily plotted on a graph.

Tables showing the average voltage and current for three voltage settings.

2V Setting:

 Resistance (Ohms) Average Voltage (V) Average Current (A) R1 1.12 0.04 R2 1.11 0.05 R3 1.09 0.07 R4 1.08 0.12 R5 0.99 0.3

4V Setting:

Conclusion

Referring back to my prediction: Based on my background knowledge and the theory I have researched I predict that as the resistance is changed this will affect the voltage, current and internal resistance. As the voltage decreases the current will slightly increase. This makes the internal resistance decrease. Alternatively if the voltage increases the current will decrease and therefore internal resistance will increase.

My prediction also suggests that the results are accurate. The results show that as the voltage decreases when the resistance is changed the current increases. And using the calculations and equations from the theory the internal resistance was also shown to decrease. This is more or less what was stated in the prediction.

Therefore I conclude that the results gathered are sufficient and overall the experiment was successful.

Limitations:

• Unidentified Faulty equipment: give changing or false results
• Environmental conditions: high room temperature may affect resistance and effect results for example.
• Inaccurate method of measuring the external resistance: may give different readings for repeats.

Improvements:

• Test equipment beforehand to ensure everything is working correctly
• Take all the results at the same time to keep experiment in similar environmental conditions throughout.
• Possible computerised way of setting resistance to make sure the value for external resistance is always for repeats.

This student written piece of work is one of many that can be found in our AS and A Level Electrical & Thermal Physics section.

## Found what you're looking for?

• Start learning 29% faster today
• 150,000+ documents available
• Just £6.99 a month

Not the one? Search for your essay title...
• Join over 1.2 million students every month
• Accelerate your learning by 29%
• Unlimited access from just £6.99 per month

# Related AS and A Level Electrical & Thermal Physics essays

1. ## In this experiment, we will measure the e.m.f. and the internal resistance of a ...

of the dry cell. With the key plug opened, the voltmeter reading (V ) is 2.6 V � 0.1 V. E.m.f of one cell = 2.6 / 2 = 1.3 V � 0.1 V. Total resistance: V = - Ir 1.40 = 2.60 - 0.16 r r = 7.50 ?

2. ## The potato - a source of EMF

However, the EMF calculated from the intercept of the graph decreased at first between 8cm and 4cm (0.71A - 0.60A) and then increased from 4cm - 2cm (0.60A - 0.67A). If I take into account the errors explained above for the internal resistance it would make sense for the EMF

1. ## Measuring the e.m.f. And Internal Resistance of a Cell

However the suitability of the techniques was doubtful. It was very difficult to get an accurate reading at a precise point because the meters kept flickering between readings.

2. ## The aim of the experiment is to verify the maximum power theorem and investigate ...

1.2 1.2 1.2 1.0 1.2 In the following calculations, we have made several assumptions: 1. Air resistance is neglect 2. The friction is evenly distributed on any surface of the sand paper (i.e. the friction should be the same over the whole sand paper.)

1. ## Investigating the Smoothing Effect of a Capacitor on a Resistive Load

I log C-1 f logV= log I - log C f From this we can expect a straight line graph with a negative gradient equal to -1. logV should be plotted along the y-axis and logC along the x-axis. log I/f is the point at which the line should intercept the y-axis.

2. ## I am going to investigate what the resistivity is of a pencil lead. ...

0.44 0.443 1.00 0.55 0.54 0.55 0.546 1.20 0.66 0.66 0.67 0.663 1.40 0.84 0.85 0.85 0.846 1.60 1.11 1.10 1.10 1.103 1.80 1.28 1.26 1.30 1.280 2.00 1.46 1.45 1.45 1.453 As you can see from the graph, the line of best fit does not pass through (0,0)

1. ## The experiment involves the determination, of the internal resistance of a cell.

L/m 1/L (m-1) 1/R (?-1) 0 0.1 0.4 0.5 0.8 1 2 4 6 8 10 0.890 0.098 0.014 0.034 0.075 0.099 0.213 0.357 0.456 0.526 0.573 1.124 10.204 71.429 29.412 13.333 10.101 4.695 2.801 2.193 1.901 1.745 ? 10.00 2.50 2.00 1.25 1.00 0.50 0.25 0.17 0.13 0.10 From the results taken in the trial of the experiment the following table was devised: R/?

2. ## Find The Internal Resistance Of A Power Supply

From Kirchhoff's second law we know that: E = IR + Ir (1) Where E is the Electromotive Force (EMF) of the power supply, maximum energy per unit charge that the power supply can deliver. R is the external (load) resistance. And I is the current flowing through the circuit.

• Over 160,000 pieces
of student written work
• Annotated by
experienced teachers
• Ideas and feedback to