”ELECTRONIC AND ELECTRICAL ENGINEERING” Laboratory I “OHM’S LAW AND KIRCHHOFF’S LAW” Student Name: Mahroo Uris Lecturer: Miss Nohaidda. Date of Experiment: 26th-February-15 Date of Submission: 5th-March-15. Abstract: The purpose of the first lab experiment is to determine the relationship between current and voltage in a circuit. The experiment is conducted to check whether the current passing through between two points is directly proportional to the potential difference or voltage across the two points when the resistance is kept constant. In this experiment we increased voltage gradually to check whether the current is also increasing or not. As the voltage increases current also increases and when the voltage decreases current decreases too. At the end of the lab, the experiment concludes that the current and the voltage have direct relation to each other when the resistance is kept constant in standard conditions. Second experiment is to verify the two important laws that plays an important part in our daily life. The two laws which are commonly takes part our known as Kirchhoff’s Current Law and Kirchhoff’s Voltage Law. KCL and KVL commonly known. The experiment tells us that in a parallel circuit the current “I” and the voltage “V” remains constant throughout. The division of current and joining is discussed in this experiment. Objective: The purpose of this experiment is to verify Ohm’s Law using resistor in DC and AC circuits. To get familiar with the series and parallel circuits. Also to get to understand the principals under Kirchhoff’s Laws. Introduction: The principal of Physics where the electric current passing through a conductor is directly proportional to the voltage across it keeping in mind that the temperature is kept constant as well as the resistance this theory is known is Ohm’s Law. Ohm’s Law can be used to solve simple circuit’s resistive electronic circuits. Ohm’s Law is given by: V=IR Where “V” is equal to voltage between two points which include resistance “R” and “I” is the current flowing through resistance. Property SI Units Voltage Volts (V) Current Ampere (A) Resistance Ohms (Ω) Kirchhoff’s circuit laws are two equations that address the conservation of energy and charge in context of electrical circuits. Kirchhoff’s laws are two equations first published by Gustav Kirchhoff in 1845. Kirchhoff’s Current Law States that any node in an electrical circuit, the sum of the current entering into that node is equal to the current leaving from that node. Kirchhoff’s Voltage Law States that the algebraic sum of the voltages across any set of branches in a closed loop is equal to zero. Apparatus: List for Experiment 1: S.NO COMPONENTS RATING QUANTITY 1. Ammeter Multimeter 1 2. Voltmeter Multimeter 1 3. Variable Power Supply 0-30V, DC 1 4. Resistance R1=? R2=? 1 5. Breadboard - 1 6. Connecting Wires - Few List for Experiment 2: S.NO COMPONENTS RATING QUANTITY 1. Ammeter Multimeter 2 2. Voltmeter Multimeter 2 3. Variable Power Supply 0-30 V, DC 1 4. Resistance R1=? , R2=? 2 5. Breadboard - 1 6. Connecting Wires - Few Experimental Methods: For Ohm’s Law: To begin the lab experiment first step was to use ohmmeter and by using ohmmeter the value of resistance R1 was to be measured and recorded into Table 3. Then the resistance was to be connected and the circuit was to be made similar to the one shown below in Figure 1. Figure 1: Circuit Diagram 1 As the circuit was created, the next step was to connect voltmeter across the resistor R1 and the ammeter was to be connected in series with the resistor. As all the components of the circuit were connected properly, the DC power supply was switched on and for different values of input voltage, “E”, voltage “V” across R1 and current “I” flowing through R1 was to be found. The readings were noted down in the table respectfully. Now with the other resistor having different value was to be used and the same procedure was to be repeated and the readings were to be taken. For Kirchhoff’s Law: Series Circuit: In this lab experiment we had to use ohmmeter to measure and record the value of the resistance R1 and R2 in table 4. Then after recording the values we were asked to connect it to the circuit as shown in figure 3 below. As the circuit the circuit was formed, the next necessary step was to switch on the DC power supply. For the values of R1 and R2, we had to record the values of VT, V1, V2 and I in the table 4. Then we were asked to check whether the RT = R1 + R2. Also we checked VT = V1 + V2. Parallel Circuit: We used Ohmmeter and measured and recorded the value of Resistance R1 and R2 in the table 5. Then we connected the circuit as shown below. We switched the DC power supply For the given values of R1 and R2 we recorded the reading for VT, V1, V2, I1, I2 and I in the table 5. Check RT= (R1 x R2) / (R1 + R2) Verify IT = I1 + I2 Voltage across parallel resistor should be same, we checked it. Result and Analysis: Table3: RESISTOR (kΩ) VOLTAGE (V) CURRRENT (mA) Practical value Theoretical value R1=4.7 3 0.635 0.635 6 1.211 1.211 9 1.879 1.879 12 2.500 2.501 15 3.100 3.100 R2=3.0 3 1.000 1.000 6 1.966 1.967 9 3.000 3.001 12 4.000 4.000 15 5.000 5.000 Sample Calculation: Below table shows the sample calculation and equation used to get theoretical values in table 3. V = IR I = V/R R1 = 4.7 k Ω R2 = 3.0 k V = 3 V V = 6 V I = 0.635mA I = 1.967mA Table 4: Study of Resistor in series and Kirchhoff’s Current Law: R1 (Ω) R2 (Ω) V1 (V) V2 (V) I (A) VT RT=VT/I V1+V2 4700 3000 6.15 3.90 0.00129 10.07 7798.45 10.05 Table 5: Study of Resistors in Parallel and Kirchhoff’s Voltage Law: R1 (Ω) R2 (Ω) V1 (V) V2 (V) VT I1 (A) I2 (A) I (A) RT=VT/I I1+I2 4700 3000 10.05 10.05 10.05 0.0021 0.0033 0.0059 1827.27 0.0055 From Table 5: For Series Circuit: RT = R1 + R2 = 7700 Ohm. (Theoretical value) VT = V1 + V2 = 10.05 (Kirchhoff’s Voltage Law Verified) From Table 6: For Parallel Circuit: RT = (R1 x R2) / (R1 + R2) = 1827.27 Ohm (Theoretical value) I = I1 + I2 = 0.0055 A (Kirchhoff’s Current Law verified. Discussion: In this Ohm’s Laws experiment which was conducted on to verify ohm’s law. The results obtained were quite similar to each other. There were very small variations between the practical value of the current and theoretical value. As the voltage value was increased, current was increasing. In this experiment I felt that there were some possibilities which would have caused errors into our readings are that there wasn’t constant temperature everywhere which might have given us some different values. Secondly the resistance should be connected to the ohmmeter directly to avoid any wrong readings. Kirchhoff’s Law, and the characteristics of current, voltage and resistance were observed in series and parallel circuits. In the series circuit the current remained the same. The current was measured using an ohmmeter and voltage using a voltmeter. However for the resistance it was equal to the algebraic sum of the individual resistors. Though the total voltage was equal to the sum of the individual voltage across the resistor. Thus the voltage conservation law the Kirchhoff’s Voltage Law was verified. However in parallel circuits the voltage remained the same and the total resistance was found by adding up the reciprocals of the individual resistors values and then taking the reciprocal of the total. The current was divided in parallel circuit but was conserved at the end proving that the current entering the circuit is equal to the current leaving it which verifies the Kirchhoff’s Current Law. Conclusion: Since we saw that the current-voltage relationship seems to be the same as one increases the other increases too which proves that the current voltage are directly proportional to each other hence proving that Ohm’s Law was verified. The results obtained through this experiment are satisfactory. From the lab experiment it is hence proved that in series circuit the current remains the same but not in parallel. In parallel current divides into branches. Also it is verified that in series circuit Kirchhoff’s Voltage Law is applied whereas in parallel Kirchhoff’s Current Law. References: http://www.physics.uoguelph.ca/tutorials/ohm/Q.ohm.intro.html http://electrical4u.com/ohms-law-equation-formula-and-limitation-of-ohms-law/ http://www.electronics-tutorials.ws/dccircuits/dcp_4.html