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Experiment no. 8

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Basic Electrical Engineering

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Experiment no. 8

  1. 1. Maharashtra Institute of Technology, Aurangabad LABORATORY MANUAL Practical Experiment Instruction Sheet EXPERIMENT TITLE : Verification of Ohm’s Law. EXPERIMENT NO.8 : MIT(T)/ETC/Basic Electrical Engineering /Manual No.1 FY(All) DEPARTMENT: Electronics & Telecommunication Engineering LABORATORY : Basic Electrical Engineering Location Part I Page 37 Aim: Verification of Ohm’s Law. Apparatus: 1. 4 varied value of resistors 2.Power supply 3. Connecting wires 4.Multimeter Theory : The most basic quantities of electricity are voltage, current and resistance. Ohm's law shows a simple relationship between these three quantities, hence this law can be considered as the most basic law of electrical engineering. This simple, easiest to remember, three character law of electrical engineering helps to calculate and analyse electrical quantities related to power, efficiency and impedance. The statement of Ohm’s law is simple, and it says that whenever a potential difference or voltage is applied across a resistor of a closed circuit, current starts flowing through it. This current is directly proportional to the voltage applied if temperature and all other factors remain constant. Thus we can mathematically express it as: V ∝I Now putting the constant of proportionality we get, V=IR This particular equation essentially presents the statement of this law where I is the current through the resistor, measured in Ampere (Ampere, or amps), when the electric potential difference V is applied across the resistor in unit of volt, and ohm(Ω) is the unit of measure for the resistance of the resistor R.It’s important to note that the resistance R is the property of the conductor and theoretically has no dependence on the voltage applied, or on the flow of current. The value of R changes only if the conditions (like temperature, diameter length etc.) of the material are changed by any means. Prepared By: Mr. S.S. Chate Approved By: Dr. G.S. Sable
  2. 2. Maharashtra Institute of Technology, Aurangabad LABORATORY MANUAL Practical Experiment Instruction Sheet EXPERIMENT TITLE : Verification of Ohm’s Law. EXPERIMENT NO.8 : MIT(T)/ETC/Basic Electrical Engineering /Manual No.1 FY(All) DEPARTMENT: Electronics & Telecommunication Engineering LABORATORY : Basic Electrical Engineering Location Part I Page 38 The applications of ohm’s law are that it helps us in determining either voltage, current or resistance of a linear circuit when the other two quantities are known to us. Apart from that, it makes power calculation a lot simpler, like when we know the value of the resistance for a particular circuit, we need not know both the current and the voltage to calculate the power dissipation since P = VI. Rather we can use Ohm’s Law V=IR I= V R To replace either the voltage or current in the above expression to produce the result P=VI= V 2 R =I 2 R These are the applications of Ohm’s law as we can see from the results, that the rate of energy loss varies with the square of the voltage or current. When we double the voltage applied to a circuit, obeying Ohm’s law , the rate at which energy is supplied (or power) gets four times bigger. This phenomena occurs because increasing the voltage also makes the current rise by the same amount as it has been explained above. Limitation of Ohm’s Law The limitations of Ohm’s law are explained as follows: 1) This law cannot be applied to unilateral networks. A unilateral network has unilateral elements like diode, transistors, etc., which do not have same voltage current relation for both directions of current. Prepared By: Mr. S.S. Chate Approved By: Dr. G.S. Sable
  3. 3. Maharashtra Institute of Technology, Aurangabad LABORATORY MANUAL Practical Experiment Instruction Sheet EXPERIMENT TITLE : Verification of Ohm’s Law. EXPERIMENT NO.8 : MIT(T)/ETC/Basic Electrical Engineering /Manual No.1 FY(All) DEPARTMENT: Electronics & Telecommunication Engineering LABORATORY : Basic Electrical Engineering Location Part I Page 39 2) Ohm’s law is also not applicable for non – linear elements. Non – linear elements are those which do not give current through it, is not exactly proportional to the voltage applied, that means the resistance value of those elements changes for different values of voltage and current. Examples of non – linear elements are thyristor, electric arc, etc. Procedure: The experiment setup consists of a simple circuit with a variable resistance and simple power source, which are 3 batteries (1.5 Volt each). The diagram beside shows the single circuit that we will use for this experiment: Choose a Voltage range and then vary the value of the resistance over the range. As expected from Ohm’s law, it will be seen the voltage range and value of the resistance chosen will be linear and the value of resistance will be perpendicular to the current. 1. Set up the apparatus to be the circuit as shown in diagram of hypothesis. 2. Set the value of electromotive force into 3 V. 3. Put the 12-ohm resistor and see the value of current in the Multimeter. Prepared By: Mr. S.S. Chate Approved By: Dr. G.S. Sable
  4. 4. Maharashtra Institute of Technology, Aurangabad LABORATORY MANUAL Practical Experiment Instruction Sheet EXPERIMENT TITLE : Verification of Ohm’s Law. EXPERIMENT NO.8 : MIT(T)/ETC/Basic Electrical Engineering /Manual No.1 FY(All) DEPARTMENT: Electronics & Telecommunication Engineering LABORATORY : Basic Electrical Engineering Location Part I Page 40 4. Change the 12-ohm resistor with 82 and 470-ohm resistor varied and repeat step 3. 5. Change the value of electromotive force into 6 V. 6. Repeat steps 3 and 4 (use 56-ohm resistor instead of 12-ohm resistor, because the value of 12-ohm resistor is too small for 6V of electromotive force). Observation Table: Experiment In Calculation Current Resistance Voltage V = IR 3 V 3 V 3 V 6 V 6 V 6 V Conclusion: Write your own conclusion. From this experiment, we can see that the values of voltages depend on how big are the values of resistors. The bigger the values of resistors, the bigger the values of electromotive force will be resulted. This shows that the voltage range and resistor value is linear to each other, while perpendicular with the value of current. For more clear details, see the table of the experiment data above. Prepared By: Mr. S.S. Chate Approved By: Dr. G.S. Sable

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