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Certificate This is to certify that I, Shaniba Rahat of class XII of Alpine Public School has successfully completely the “To study various factors on which the internal resistance / EMF of a cell depends Investigatory Project as prescribed by Miss Alina Akhtar ma'am Principal’s Signature Signature of Signature of External Examiner Internal Examiner Acknowledgement I would like to express my thanks of gratitude to our Principal mr. Shakeel Ahmed sirfor giving me the golden opportunity to do this wonderful project on the topic “Eactors on which internal resistance of cell depends" which has helped me in doing a lot of research. I would extend my heartiest thanks to my Physics teacher Miss Alina Akhtar ma'am for providing me with all the support I required at all times. I would like to gratefully thank my parents for providing me with all the facilities and a favourable environment at home. I would also thank my friends who have given me support and helped me in finalizing the project in the given time frame. THANK YOU Introduction There is a great need of batteries in our daily use electronic appliances and the use is increasing every day. Thus, the batteries need to be made more powerful so that their potential can be increased greatly. This project report is based on practical analysis for the factors affecting the internal resistance of a cell. When the internal resistance of the cell is decreased we can increase the potential difference across it, and hence make it more reliable. Internal Resistance The resistance within a battery, or other voltage source, that causes a drop in the source voltage when there is a current. Internal resistance Internal resistance is defined as the resistance offered by the electrolyte of the cell to the flow of ions. Its S.1. unit is Ohm (Q). v Emt,£ gradient =r For a cell of e.m.f. (E) and internal resistance (r), connected to an external resistance (R) such that (I) is the current flowing through the circuit, » THEORY The internal resistance of a cell is the resistance offered by its electrolyte to the flow of ions. The internal resistance of a cell * Is directly proportional to the distance between the electrodes. Let x be the distance between the electrodes, then, rox * Is inversely proportional to facing surface area of the electrodes in electrolyte. Let A be the surface area of the electrodes, then, ral/A * Decreases with increase in temperature of electrolyte. * Is inversely proportional to concentration of electrolyte. The internal resistance of a cell is given by: r=(E-V)/I >» CIRCUIT DIAGRAM Power Supply A a J B Shunt The above circuit includes: v A power supply ¥ Two one way keys v A galvanometer 7. Determine the position of the null point accurately using a set square and measure the balancing length (11) between the null point and the end P. 8. Next introduce plugs in both keys K; and Kz. At the same time, take out a small resistance (1 - 5W) from the shunt resistance box connected in parallel with the cell. 9. Slide the jockey along a potentiometer wire and obtain the null point. 10. Measure the balancing length (lz) from end P. Record these observations. 11. Now keep the electrodes 12 cm apart. 12. Then remove the plugs of keys K1 and Kz. Wait for some time and repeat steps 7 to 10. 13. Next, keep the electrodes 9 cm apart to obtain another set of observations. To study variation of internal resistance with area of electrodes 14. Keeping all other factors constant, increase the area of electrodes in the electrolyte by dipping them into the electrolyte at different depths for each observation. 15. Obtain three such observations by repeating steps 7 to 10. Record your readings. To study variation of I resi i concentration of electrolyte. 16. Keeping all other factors constant, decrease the concentration of electrolyte by adding distilled water for different observations. 17. Obtain three such observations by repeating step 7 to 10. Record your readings. 0.3 660.5 77.2 1.77 0.3 660.5 108.3 2.51 Table for effect of separation between electrodes: S. No, Separation | Balancing | Balancing | Internal r/d between point |i point la resistance electrodes (cm) (cm) r(Q) d (cm) 1; 1.2 326.6 276.9 0.456 0.38 2. 2.5 320.7 219.1 0.45 0.38 3. 3.7 660.5 350.9 1.406 0.38 Table for effect of temperature: S. | Temperature l2 Resistanc | Internal Tr No. T (°C) (cm) (cm) e Resistance R (2) r(Q) ad 1, 1.2 326.6 | 276.9 | 0.456 0.38 | 301.44 2. 2.5 320.7 | 219.1 | 0.95 0.38 | 291.96 3. 3.7 660.5} 350.9 | 1.406 | 0.38 | 283.87 >_ RESULT AND INFERENCES * The Electromotive Force of the cell is constant and is equal to E=0.98 Volt. * The internal resistance of a cell is directly proportional to the separation between the electrodes. rad * The internal resistance of a cell is inversely proportional to the area of the electrodes dipped in electrolyte. >» SOURCES OF ERROR * The auxiliary battery may not be fully charged. * The potentiometer wire may not be of uniform cross-section and material density throughout its length. « End resistances may not be zero. Flowchart CONCLUSION Factors Affecting Internal Resistance of a Cell Distance between the electrodes Directly Proportional Area of electrodes Inversely Proportional Temperature of Electrolytes Inversely Proportional Concentration of Electrolyte Inversely Proportional 
