S.V.M. PUBLIC SCHOOL
Physics ProjectAISSCE 2015-16
SUBMITTED TO: SUBMITTED BY: Mr. Purushotam Sir Aayush Tambi (H.O.D. Physcis ) XII(B)-SCIENCETo Study Various Factors On Which The Internal Resistance /EMF Of A Cell Depend
CERTIFICATEThis is to certify that AAYUSH TAMBI a student of class 12 has successfully completed the research project on the topic To Study Various Factors On Which The Internal Resistance /EMF Of A Cell Depend under the guidance of Mr. Purushotam Khandelwal (subject teacher). This project is absolutely genuine and does not indulge in plagiarism of any kind. The references taken in making this project have been declared at the end of the project.
Mr. Purushotam KhandelwalH.O.D.Physics
INDEX Certificate Acknowledgement Introduction Apparatus Circuit Diagram Theory Procedure Observation Conclusions Precautions Source Of ErrorACKNOWLEDGEMENTI would like to express my sincere gratitude to my chemistry mentor Mr.Purushotam Khandelwal for his vital support ,guidance and encouragement ,without which this project would not have come forth. I would also like to express my gratitude to the lab assistant Mr. MADAN LAL and Mr. BHAWAR LAL for their support during making of this project .
Last but not the least I thank my PARENTS for their encouragement and support .
AAYUSH TAMBI XII (B) SCIENCE APPARATUS1. A PotentiometerIt is a device used to measure the internal resistance of cell , to compare the e.m.f. of two cells and potential difference across a resistor. It works on the principle that when a constant current flows through a wire of uniform thickness and material, potential difference between its two points is directly proportional to the length of the wire between the two points. It consists of along wire of uniform cross section, 4 to10m long, of material having high resistivity. These wires are streched parallel to each other.2. An Ammeter Anammeterismeasuring instrumentuse to measure the current in acircuit. Electric currents are measured inamperes(A), hence the name. Instruments used to measure smaller currents, in the milliampere or microampere range, are designated asmilliammetersormicroammeters.The majority of ammeters are either connected in series with the circuit carrying the current to be measured (for small fractional amperes), or have their shunt resistors connected similarly in series. In either case, the current passes through the meter or (mostly) through its shunt.
3. GalvanometerA galvanometer is a device (instrument) used for detecting feeble electriccurrents in circuits.It is always connected in series in the circuit in which current is to be detected.4. A Battery (battery eliminator) A combinations of cells is called a battery. 5. Two Way Keys It has one long brass block and two small brass blocks perpendicular to it,fixed on an ebonite base.6. A Rheostat of low resistance It is a variable resistance device and is commonly used for adjusting the strength of electric current in an electric circuit.It is made by wrapping a long wire of constantan round a non conducting ceramic cylinder7. A Cell ( Leclanche or Daniel cell )A cell is a device used as source of electric current in various electricalexperiments.When a cell is connected across a conductor (electric circuit) then it maitained potential difference between its ends,to provide a suppply of electric current continuously.8. BurnerBurner is a mechanical device that burns a gas or liquid fuel into a flame in a controlled manner.9. Tripod StandA tripod is a portable three-legged frame, used as a platform for supporting the weight and maintaining the stability of some other object.
10. Wire GauzeA wire gauze is a type of of very fine, woven wire that looks like netting.11. A High Resistance12. A Jockey13. A set square connecting wires 14. Water Bath15. Thermometer ( 0-100 oC )
Circuit diagram
TheoryTHE INTERNAL RESISTANCE of a cell cell is the resistance offered by itseletrolyte to the flow of ions. The internal resistance of a cell1. is directly proportional to distance between the eletrodes.2. inversely proportional to facing surface area of eletrodes in eletrolyte.3. decrease with increase in temperature of eletrolyte.4. inversely proprotional to concentration of eletrolyte.The internal resistance of a cell is given by where l1 and l2 are the balancing lengths without resistance and with resistance (shunt), respectively and R is shunt resistance in parallel with the given cell.Procedure
STEP 11. Arrange apparatus as shown in circuit diagram.
2. Clean the ends of the connecting wires with sand paper and make tight connections according to the circuit diagram.
3. Tight the plugs of the resistance box.
4. Check the e.m.f. of the battery and cell and see that the e.m.f. of the battery is more than that of the given cell, null point will not be obtained(E'>E).
5. Take maximum current from the battery, making rheostat resistance small.
6. To test the correctness of the connections (Insert the plug in the key K1 and note the ammeter reading. Take out 2000 ohm resistance plug from the resistance box. Place the jockey first at the end P of the wire and then at the end Q. If the galvanometer shows deflection in opposite directions in the two cases ,the connections are correct).
7. Without inserting the plug in the key K2 adjust the rheostat so that a null point is obtained on the fourth wire of the potentiometer.
8. Insert the 2000 ohm plug back in its position in resistance box and by slightly adjusting the jockey near the previously obtained position of null point, obtain the null point position accurately, using a set square.
9. Measure the balancing length l1 between this point and the end P of the wire.
10. Take out the 2000 ohm plug again from the resistance box R.B. Introduce the the plugs in the key K1 as well as in key K2 Take out a small resistance (1-5 ohm) from the resistance box R connected in parallel with the cell.
11. Slide the jockey along the potentiometer wire and obtain null point.12. Insert the 2000 ohm resistance plug back into its position in R.B. and if necessary make further adjustments for sharp null point.
13. Measure the balancing length l2 from end P.
14. Remove the plug keys at K1 and K2. Wait for sometime and for the same value of current (as shown by the ammeter) repeat steps 7 to 13.
15. Repeat the observations for different values of R repeating each observation twice.
16. Calculate the internal resistance of cell by using the above relation for r
STEP-2To see the effect of distance between the electrodes on internal resistance keeping the others factors constant, vary the separation between the electrodesand measure the internal resistance in each case.Draw a graph between the separation between the electrodes and the internal resistance.
STEP-3To see the effect of area of electrodes in electrolyte on internal resistance keeping the other factors constant, increase the area of electrodes in electrolyteby dipping them into electrolyte and measure the internal resistance of cell in each case. Plot the graph between the two.
STEP-4To see the effect of temperature of electrolyte on the internal resistance by keeping the other factors constant Keep the primary cell in water bath to heat the electrolyte. Determine the resistance at various temperatures. Plot the graph between the two.
STEP-5To see the effect of concentration of electrolyte on internal resistance by keeping the other factors constant. Decrease the concentration of electrolyte by adding the distilled water and determine the internal resistance of cell in each case. Plot the graph betweenthe two.CONCLUSION The emf of a cell is constant E =V. The internal resistance of a cell is directly proportional to the separation between electrodes. The internal resistance of a cell is inversely proportional to the area of the electrodes dipped in electrolyte. The internal resistance of a cell is inversely proportional to the temperature of electrolyte. The internal resistance of a cell is inversely proportional to the concentration of the electrolyte.
precautions The connection should be neat , clean and tight. The plugs should be introduced in the keys only when the observations are to be taken. The positive poles of the battery E and cells E1 and E2 should, all connected to the terminal at the zero of the wires. The jockey key should not be rubbed along the wire. It should touch the wire gently. The e.m.f. of the battery should be greater than the e.m.f. s of the either of the two cells. The ammeter reading should remain constant for a particular set of observation . If necessary ,adjust the rheostat for this purpose.
Some high resistance plug should always be taken out from resistance box before the jockey is moved along the wire . The e.m.f. of the battery should be greater than that of the cell. For one set of observation the ammeter reading should remain constant. Current should be passed for short time only ,while finding the null point. Rheostat should be adjusted so that initial null point lies on last wire off the potentiometer . Cell should not be disturbed in the experiment. Jockey should not be rubbed against the potentiometer wire.
Source of error1. The auxiliary battery may not be fully charged.2. The potentiometer wire may not be of uniform cross-section and material density .3. End resistance may not be zero.
BIBLIOGRAPHY
New corses in Physics- PRADEEPS PUBLICATIOS Comprehensive Practical Physics - LaxmiPublications www.cbse.nic.in www.icbse.com www.cbseguess.com www.google.com My Physics Mentor Mr.Purushotam Khandelwal
