Investigate methods of finding and comparing the e.m.f and internal resistance of different cells and power supplies and factors that can affect these values.

5. Repeat experiment with another power source.

Results

Source1: Mitsubishi R20-1.5V

Resistance/?

Current/mA

Voltage1/V

Voltage2/V

Average Voltage/V

500

2

.36

.36

.36

450

3

.36

.36

.36

400

4

.36

.36

.36

350

4.5

.35

.36

.355

300

5

.35

.36

.355

250

6

.35

.35

.35

200

7

.35

.35

.35

50

0

.34

.35

.345

00

4

.33

.34

.335

50

26

.32

.32

.32

Source2: Sony R6-1.5V

Resistance/?

Current/mA

Voltage1/V

Voltage2/V

Average Voltage/V

500

2

.46

.46

.46

450

2.5

.46

.45

.455

400

3

.46

.45

.455

350

3.5

.45

.45

.45

300

4

.45

.45

.45

250

5

.45

.44

.445

200

6

.44

.44

.44

50

8

.44

.43

.435

00

3

.42

.42

.42

50

25.5

.39

.39

.39

Source3: Duracell R6-1.5V

Resistance/?

Current/mA

Voltage1/V

Voltage2/V

Average Voltage/V

500

2

.47

.47

.47

450

2.5

.47

.47

.47

400

3

.47

.47

.47

350

3.5

.47

.47

.47

300

4

.46

.46

.46

250

5

.46

.46

.46

200

6

.46

.46

.46

50

8.5

.45

.45

.45

00

0.3

.44

.43

.435

50

26

.39

.39

.39

Source4: Four-Way Rectified Output Power Supply-2V

Resistance/?

Current/mA

Voltage1/V

Voltage2/V

Average Voltage/V

500

8

3.32

3.33

3.325

450

8

3.32

3.32

3.32

400

8.5

3.31

3.32

3.315

350

0

3.31

3.31

3.31

300

1.5

3.29

3.30

3.295

250

3

3.27

3.28

3.275

200

7

3.25

3.26

3.255

50

22

3.22

3.23

3.225

00

32

3.19

3.20

3.195

50

62

3.15

3.15

3.15

Below is a list of the e.m.f and internal resistance of each of the cells and power supplies.

Source

Electromotive force/V

Internal resistance/?

Mitsubishi R20 1.5V

.364

.9

Sony R6 1.5V

.463

3.5

Duracell R6 1.5V

.482

4.4

Four way rectified output power supply 2V

3.355

5.0

Analysis of results

According to the result, the four-way rectified output power supply gave the largest e.m.f and internal resistance, and the Mitsubishi R20 gave the smallest values. This proves that the source with the largest voltage gave the largest e.m.f and largest internal resistance. However, it does not prove that the internal resistance is due to chemical reaction and amount or not, because the Mitsubishi R20 had more chemical content than the Sony R6 or the Duracell R6. Therefore it disproves the theory that internal resistance is greater in sources with greater chemical content, although chemical reaction does affect internal resistance as it provides heat that is also internal resistance.

Errors and improvements

The cells and supply used should have had an initial voltage of the same value to make the test much fairer. This would mean that the cells would have similar starting voltage of about 1.5V rather than a varied range.

The power supply used was supposed to give voltages less than 2V. Instead it gave values within the 3V-4V ranges. Either a fixed voltage power supply, or the supply set to about 2V (through the use of an external resistor) should have been used to gather more efficient results.

A second power supply could be used to compare the values of e.m.f and internal resistance. This could be the second set of p.d values and may give a more accurate result. The power supply could be set to 1.5V rather than 2V, or the additional 0.5V could be eliminated from the initial 2V by adding a resistor in series with the power supply. This method can also be tested on the four way rectified output power supply.

There should have two or more R20 cells to compare the values from the Mitsubishi cell. This would show whether the e.m.f was similar or not, the experiment was designed to compare e.m.f and internal resistance.

The e.m.f and internal resistance, for the same cell type at the same initial voltage, could have been averaged to get a more accurate result, or several values for the gradient could be taken and the internal resistance could be the average result. Then the formula stated above

E.m.f = current (external resistance + internal resistance)

could be used to discover the e.m.f.

Heat is also a form of resistance and may have affected the results. This means that the values may be inaccurate, depending on the length of time each source was on for and the amount of chemical reactions that had taken place in this time. The time duration should be recorded or set to a specific period, for on and off. This means that the source will give more accurate results and the test would be considered fairer.

Evaluation

The results of the experiment could not only be inaccurate, but can also prove to be inconclusive, as there was a great deal of errors that could cause any number of faults in the experiment. The errors include:

. Initial voltage not equal to 1.5V.

2. The time period for which a source has been turned on or off for.

3. The temperature of the source at different intervals in time.

4. The age of a source (also affects the output voltage).

The faults that could occur are:

. Imprecise measurements of the terminal p.d and the current. Inaccurate values will give imprecise results for the e.m.f and internal resistance.

2. High temperatures can cause a resistance that would decrease the current.

However, these errors and faults would give slightly imprecise results, they would have little effect on the outcome of the experiment. This means that the experiment should still be considered a valid success.

Overall the experiment is correct and does prove that the greater the supply voltage, the greater e.m.f and internal resistance. Yet, it neither proves nor disproves the case of greater chemical content giving greater internal resistance.

Name: Mohammed Husnat 1 Candidate number: 9834