Measuring the e.m.f. And Internal Resistance of a Cell
Planning
I wish to find out the electromotive force (e.m.f.) and Internal Resistance of a direct current battery cell.
Circuit Diagram
. Set up apparatus as shown.
2. Use ammeter to adjust variable resistor to vary of currents.
3. Read voltmeter value and record.
4. Disconnect circuit and take e.m.f reading from voltmeter across cell.
5. Repeat for another 9 resistor settings. Use variable resistor and ammeter to adjust the set up to get a range of 0.1 to 1.0A.
6. Repeat entire experiment to get more accurate average.
Safety Aspects
. Do not have circuit connected up for too long, this will run the battery down and may cause it to heat up and maybe explode.
2. Wear safety goggles and lab-coats during experiment.
3. Follow standard laboratory safety procedures.
Apparatus
0 - 1.0A analogue ammeter
2 digital voltmeters
1 variable resistor
1 cell
8 connecting wires.
Safety goggles and lab-coat
Paper and pen
Arranging Evidence
Results
Current (Amps)
Potential Difference (V)
2
3
Average
0.1
.46
.47
.46
.46
0.2
.42
.42
.41
.42
0.3
.36
.39
.36
.37
0.4
.33
.33
.33
.33
0.5
.27
.29
.28
.28
0.6
.24
.23
.23
.23
0.7
.18
.19
.20
.19
0.8
.13
.15
.14
.14
0.9
.10
.09
.11
.10
.0
.04
.03
.06
.04
Using these results I will be able to draw a graph to find the e.m.f. and the internal resistance of the cell.
Calculating Internal Resistance
The current is the same in any part of the circuit and the electromotive force = the sum of the potential differences.
Planning
I wish to find out the electromotive force (e.m.f.) and Internal Resistance of a direct current battery cell.
Circuit Diagram
. Set up apparatus as shown.
2. Use ammeter to adjust variable resistor to vary of currents.
3. Read voltmeter value and record.
4. Disconnect circuit and take e.m.f reading from voltmeter across cell.
5. Repeat for another 9 resistor settings. Use variable resistor and ammeter to adjust the set up to get a range of 0.1 to 1.0A.
6. Repeat entire experiment to get more accurate average.
Safety Aspects
. Do not have circuit connected up for too long, this will run the battery down and may cause it to heat up and maybe explode.
2. Wear safety goggles and lab-coats during experiment.
3. Follow standard laboratory safety procedures.
Apparatus
0 - 1.0A analogue ammeter
2 digital voltmeters
1 variable resistor
1 cell
8 connecting wires.
Safety goggles and lab-coat
Paper and pen
Arranging Evidence
Results
Current (Amps)
Potential Difference (V)
2
3
Average
0.1
.46
.47
.46
.46
0.2
.42
.42
.41
.42
0.3
.36
.39
.36
.37
0.4
.33
.33
.33
.33
0.5
.27
.29
.28
.28
0.6
.24
.23
.23
.23
0.7
.18
.19
.20
.19
0.8
.13
.15
.14
.14
0.9
.10
.09
.11
.10
.0
.04
.03
.06
.04
Using these results I will be able to draw a graph to find the e.m.f. and the internal resistance of the cell.
Calculating Internal Resistance
The current is the same in any part of the circuit and the electromotive force = the sum of the potential differences.