• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

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

Extracts from this document...

Introduction

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 1. 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 1. 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) 1 2 3 Average 0.1 1.46 1.47 1.46 1.46 0.2 1.42 1.42 1.41 1.42 0.3 1.36 1.39 1.36 1.37 0.4 1.33 1.33 1.33 1.33 0.5 1.27 1.29 1.28 1.28 0.6 1.24 1.23 1.23 1.23 0.7 1.18 1.19 1.20 1.19 0.8 1.13 1.15 1.14 1.14 0.9 1.10 1.09 1.11 1.10 1.0 1.04 1.03 1.06 1.04 Using these results I will be able to draw a graph to find the e.m.f. ...read more.

Middle

Therefore, if the equation of the line can be found then the e.m.f. can also be found. By using the results from the gradient calculations I know that the gradient is -0.47 � 0.03. If I use a pair of co-ordinates that lie on the line I can find the constant value, C, using the equation y - y1 = m (x - x1). Using co-ordinates (0.2,1.415) y - 1.415 = -0.47 (x - 0.2) y - 1.415 = -0.47x + 0.094 y = -0.47x + 1.509 This means that C must equal 1.51 (3sf). To find the error in this value I substituted the gradients and a set of points for the minimum line and maximum line in to the equation E = Ir + V. For the maxm line: E = 0.86 x 0.49 + 1.1 E = 1.52 (3sf) For the minm line: E = 1.0 x 0.45 + 10.5 E = 1.50 (3sf) The difference between these two values and the values calculated is 0.01. Therefore the electromotive force of the cell = 1.51�0.01V(3sf) Evaluating Evidence These were the possible sources of error: * As I was using an analogue ammeter the needle that is used to read the values off is slightly higher than the actual scale so to enable a completely accurate reading you have to look directly down at it. ...read more.

Conclusion

Although the ammeter could have been more accurate by having a smaller error and it may even be more precise if two or even three people were to perform the experiment together. One to turn the circuit on and off, one to take the voltmeter reading and one to take the ammeter reading. This way there is no loss of accuracy due to the time delay between taking readings that is caused by the operator. As the technique used was very accurate and precise, this made the conclusions drawn also very accurate. Although there may have been a human error made when drawing the best-fit, maximum and minimum lines on the graph and reading the results off accurately. To confirm my final value of e.m.f. I found the e.m.f. of the cell in the circuit each time I took a reading. These were the results. Current (Amps) E.M.F. taken from Voltmeter 1 2 3 Average 0.1 1.50 1.51 1.51 1.51 0.2 1.51 1.51 1.50 1.51 0.3 1.51 1.52 1.50 1.51 0.4 1.50 1.51 1.50 1.50 0.5 1.52 1.50 1.50 1.51 0.6 1.51 1.50 1.50 1.50 0.7 1.50 1.50 1.50 1.50 0.8 1.49 1.50 1.49 1.49 0.9 1.50 1.49 1.48 1.49 1.0 1.48 1.49 1.48 1.48 These show that the e.m.f value is actually around 1.50V, compared with my final result of 1.51V. This shows that the techniques appear to be very accurate and precise. This table also shows that at times the value overlaps the result I found which adds weight to the conclusion that my answer is accurate. Alice Salt ...read more.

The above preview is unformatted text

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

See related essaysSee related essays

Related AS and A Level Electrical & Thermal Physics essays

  1. Marked by a teacher

    Internal Resistance of a cell

    5 star(s)

    below: Measured each cell combination and then compare the prediction for each cell combination Identified which combination would be used if you wanted an EMF larger than that from a single cell Identified which combination is intended when cells are said to be "in series" and which intended when they are "in parallel".

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

    Therefore, the longer time is duration of the experiment, the larger is the internal resistance of the dry cell. As a result, we should not leave the circuit connected longer than necessary to take the readings.

  1. The potato - a source of EMF

    Internal Resistance: The internal resistance when the electrodes are 4cm apart is approximately half of what the internal resistance is at 8cm apart. However, the internal resistance does not decrease as much from when the electrodes are then moved to 2cm apart, therefore the distance between electrodes is not proportional

  2. Investigating the Emf and the internal resistance of a dry cell.

    The internal resistance = 0.57 - 0.05 = 0.07 r = 0.5 0.07 Emf The Emf of a cell is the y-intercept of the line on the graph. Therefore: The Emf of the line of best fit = 1.68v Due to the uncertainty of the results I will use the

  1. Investigation On The Resistivity Of Apples. Since we are measuring the resistance of an ...

    Total Average Resistance (� 0.05 x 103 ?) 1 66.4 � 3.2 2 104.8 � 3.0 3 114.3 � 2.2 4 125.1 � 4.8 5 165.8 � 4.6 The uncertainty for the average resistance for each length of apple is: Largest percentage error: We are not quite confident with our results.

  2. Free essay

    Finding the internal resistance of a solar cell

    product moment correlation coefficient reflects the degree of linear relationship between two variables. It ranges from +1 to -1. A correlation of +1 means that there is a perfect positive linear relationship between variables. A correlation of -1 means that there is a perfect negative linear relationship between variables.

  1. Sources of e.m.f. – internal resistance.

    A source of e.m.f. connected to an external circuit will dissipate some of its energy in its internal resistance, and transfer the rest to the external circuit. It is often desirable to transfer as much electrical power as possible from a source to a load, for example when an aerial is connected to a television.

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

    If it is present, we should remove all of them before we start the experiment. On top of that, it is very difficult for human eyes to take the readings from spring balance, as the reading of the balance is not constant throughout the whole experiment.

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