Ohms Law and Direct Current - Lab Report Example

Ohm’s Law and Direct Current Name Course Institution Instructor Experimental Date Submission Date Table of Contents Table of Contents 2 1.0 Abstract 3 2.0 Introduction 3 2.1 Aims 3 3.0 Ohm’s Law 4 4.0 Materials and Method 6 4.1 Apparatus 6 4.2 Procedure 6 4.3 Results and Calculations 7 4.4 Analysis 8 5.0 Task 2: Estimate the Resistance of an Unknown Resistor 9 5.1 Results and Calculations 10 5.2 Analysis 11 6.0 Conclusion 12 7.0 References 14 1.0 Abstract This report describes an experimental method that was used to validate Ohm’s law; a relationship between electric current and potential difference. The experiment involves use of various electronic components including resistors, digital multi-meters and voltmeters. A simple circuit was constructed from these components. Adjustments were made from the variable power supply to produce various current and voltage values which were recorded and graphically represented with the aim of ascertaining Ohm’s law. The relationship was also used to determine the value of unknown resistance. When current and voltage values through unknown resistor are known, Ohm’s law can be used to calculate the magnitude of resistance offered by that element. Two circuit experiments were used for this case. 2.0 Introduction Ohm’s law is an experimental formula relating potential difference across a conductor to the current through the same conductor. According to Ohm’s law the product of current and resistance is equal to voltage across the conductor. In view of the fact that current and voltage values were being recorded, Ohm’s law could be used to calculate the resistance of the conductor that was in use. Verification was possible through the comparison of calculated values and nominal values. This report describes the Ohm’s law and offers a detailed explanation of the experimental procedure of proving it. Two tasks were involved for this case. Formal definitions are given together with their mathematical expressions. 2.1 Aims The purpose of this experiment was to: Familiarise with resistor colour codes and the practical values of resistors Verify Ohm’s law Familiarize with tolerance and power rating of resistors Familiarize with use of a digital multi-meter and an AVO for measuring voltage, current and resistance 3.0 Ohm’s Law It is a fundamental law for comprehending electrical principles. It states that the current passing through a conductor is directly proportional to the potential difference applied across the ends provided the temperature and other physical conditions remain constant. If is taken to be the current and is taken to be the voltage drop, then according to Ohm’s law, . Introducing a proportionality constant represented by, the relationship becomes; . Or or This expression is referred to as Ohm’s law. The proportionality constant is referred to as resistance of the conductor. Resistance is that characteristic of materials that tends to inhibit movement of electrons. It is measured in ohms (). Electric current is the rate of flow of charge through a conductor or simply the flow of electrons from positive terminal towards the negative terminal. It is expressed as. Its SI unit is ampere (A). There are three different types of currents. They include; direct current, pulsating direct current and alternating current. Direct current was used in this experiment and it originated from Direct current power supply (PS). With this type of current, electrons move in only one direction in a conductor. An Ammeter is used to measure current. An AVO multimeter was set to measure electric current in this experiment. The AVO multimeter was connected in series because it is a low resistance instrument. It does not inhibit the flow of current. Voltage or potential difference is the electrical pressure resulting to flow of electrons. In simple terms, it is the amount of work done in moving a unit charge through a conductor. The quantity of electrical pressure is expressed in volts. A mathematical expression for this is; Potential difference = Work done (Joules)/Charge moved (Coulombs) Where; ; The quantity of work done ; The amount of charge A voltmeter is used to measure voltage or potential difference. In this experiment, a digital multimeter (DMM) was set to measure the voltage drop in the resistor. It was connected in parallel to the resistor. This is due to the fact that it has a very high resistance to flow of current. It therefore permits little current to pass through. Ohm’s law is useful in the calculation of potential difference across a conductor, resistance offered by a conductor and the current passing through the conductor provided that any two other values are known. 4.0 Materials and Method 4.1 Apparatus Strip board Soldering Iron Variable DC Power Supply (PS) Digital Multimeter (DMM) AVO Multimeter Two 0.4W carbon resistors 4.2 Procedure Task 1: Ohm’s law for the resistor To ascertain Ohm’s law, a circuit was created for experimental analysis. A diagrammatic representation of that circuit is given below; AVO Ps R1 DMM The circuit was connected as shown above. While connecting, variable voltage output from the power supply was set at a zero and the power supply unit was switched off. Variations were then made on the voltage output from 0 to 15and the corresponding current values were taken and recorded. Current values were recorded in Milliamperes. A graph of voltage against electric current for these values was drawn and its gradient determined. 4.3 Results and Calculations Voltage V (v) Current I (mA) 0.00 0.00 0.99 1.00 1.93 1.85 2.86 2.90 3.78 3.90 4.80 4.80 5.72 5.80 6.71 6.70 7.64 8.50 8.57 8.60 9.49 9.60 10.98 11.00 11.92 12.50 13.93 13.93 14.96 14.96 4.4 Analysis The experimental value of resistance when Ohm’s law is applied is. The nominal value of the resistor used as indicated by digital multimeter is. Variation between the nominal and experimental values is as a result of errors encountered. Percentage error = Estimation of the colour band resistor (Brown, black, red and gold) .Tolerance: Tolerance of the resistor used does not lie within the tolerance value of this resistor. The power dissipated in the resistor when 10V is applied. Power is given by; Substituting the values then; 5.0 Task 2: Estimate the Resistance of an Unknown Resistor To estimate the resistance of an unknown resistor, a circuit was set up as shown below. It was similar to the experiment in task 1 difference being the change of resistor. AVO Ps R2 Dmm The circuit was connected as shown above. While connecting, variable voltage output from the power supply was set at a zero and the power supply unit was switched off. Variations were then made on the voltage output from 0 to 15and the corresponding current values were taken and recorded. Current values were recorded in Milliamperes. 5.1 Results and Calculations Voltage drop V (v) Current I (A) 0.0053 0.00 0.7773 0.036 1.639 0.076 3.000 13.000 3.890 18.000 4.860 23.000 5.820 28.000 6.770 33.000 7.81 38.000 Resistor got burnt beyond this value A graph of voltage against electric current for these values was drawn and its gradient determined. 5.2 Analysis The estimated value of the resistor is. It is given by the gradient of the graph. At 7.81 volts, the resistor ceased from working. At this point, the tolerance band was exceeded. 6.0 Conclusion The experiment on task 1 was able to prove the validity of Ohm’s law. The nominal value was comparable to the experimental value. Variation was brought about by errors experienced when experimenting. It was able to show the relationship between voltage and current. In addition to this, the same findings were used to estimate the value of resistance used in each case. In task 2, the set up was used to estimate the value of unknown resistance. Similarly, there was a direct relationship between the current values and voltage values. As stipulated by Ohms law, plotting a graph of the voltage against current, the resultant graph is a straight line graph passing through the origin. Its gradient gives the value of resistance of the element used. In that matter exhibits the importance of this experimental method. Sources of Errors The possible sources of errors were; Resistance from wires used Dirty terminals could have resulted to inefficiency Voltage drop as a result of prolonged withdrawal of charges from direct current source Possible Solutions to these Errors Use of thicker wires to reduce resistance Ensure that the terminals are clean before the experiment begins Switching off the circuit when not in use 7.0 References Lerner L, S. Physics for Scientists and Engineers (Vol2). Burlington: Jones & Bartlett Learning, 1997. Kubala, T, S. Electricity. New York: Cengage Learning, 2008. Read More