Kathmandu University Department of Electrical and Electronics Engineering BASIC ELECTRICAL LAB (ENGG 103)

Transcription

1 Kathmandu University Department of Electrical and Electronics Engineering BASIC ELECTRICAL LAB (ENGG 103) EXPERIMENT 1:- Resistor Color Coding and Verification of Ohm s Law, KVL, KCL, Voltage and Current Divider Circuit Objectives: 1. Familiarization of resister color coding and tolerances. 2. Get familiar with the use of the GPC-3020D power supply digital multimeter and breadboard. 3. Verification of ohm s law and theory of voltage and current division rule. Materials and Equipments Required: Theory: 1. Digital multi-meter (GDM-352) 2. Power supply (GPC-3020D) 3. Resistors 1 KΩ (1/4 W) [4], 10KΩ (1/4 W) [4] 4. Breadboard. i) Resistor Color Coding: Each resistors value is designated in terms of color code usually four band. Each color band represents a number and the order of the color band will represent a number value. For four band resistor color code; the first 2 color bands indicate a number. The 3rd color band indicates the multiplier or in other words the number of zeros. The fourth band indicates the tolerance of the resistor +/- 20%, 10% or 5%. Color Black Brown Red Orange Yellow Green Blue Violet Gray White VALUE For Tolerance i) Gold: 5% ii) Silver: 10% iii) Other: 20% ii) Ohm s Law: In electrical circuits, Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference or voltage across the two points, and inversely proportional to the resistance between them, provided that the temperature remains constant.

2 where V is the potential difference measured across the resistance in units of volts; I is the current through the resistance in units of amperes and R is the resistance of the conductor in units of ohms. iii) iv) v) Kirchhoff s Voltage Law: The algebraic sum of voltages around a close loop is always zero. Kirchhoff s Current Law: The algebraic sum of all incoming of outgoing currents in an electric node is always zero. Voltage Divider Rule: In a series connection of resistors the total voltage supplied is divided across resistor and the current across each resistor is constant. The voltage across i th resistor with n resistors in series is given by formula:... vi) Current Divider Rule: When there is more than one path for current then current is divided. For two resistors in parallel; the current is divided according to: i.e. the current flows maximum in low value of resistor. Circuit Diagram: i) Circuit Diagram for KVL, KCL, Voltage Divider and Current Divider analysis Figure 1

3 Procedure: a) Resistance color code Choose any four random resistors and note the different bands of color of resistor. Gold and silver color band are tolerance band so start from different side if there are four color bands only. Calculate the range resistance value can have. Measure the value of resistor using multimeter. b) Ohm s law, KVL, KCL, Voltage Divider and Current Divider Rule Connect the circuit as shown in figure 1 on the breadboard where R1, R2, R3, R4 are the resistors used in resistance color code experiment. Set the value of voltage source into 5 volt. Measure the potential difference across resistors R1, R2, R3, R4 using multimeter. Similarly connect the multimeter in series with its probe on current measurement to measure the value of current in each branch Repeat the experiment for V=10V and 15V. NOTE: Remember the multimeter also has its own internal resistance, hence when measuring voltage its internal resistance (which is high in this case in Mega ohm range) is in parallel with the resistance between two points where p.d. is to be measured. So reading value is slightly less than actual value. And when measuring current its internal resistance (which is small) is in series with circuit, so reading value of current is slightly less than actual value of current flowing in the circuit. Observations: i) Resistor Color Code S.N. First Band Second Band Third Band Fourth Band Range of Resistor value Measured Value from multimeter R 1 R 2 R 3 R 4

4 ii) Ohm s law, KVL, KCL, Voltage Divider and Current Divider Tabulate the measured value for circuit 1. V V 1 V 2 V 3 V 4 V 3 +V 4 V 1 +V 2 I 1 I 2 I I 1 +I 2 V 1 /I V 2 /I 1 V/I 5 V 10 V 15 V Conclusions and Inference:

5 Exercise: For the circuit given in figure 1 calculate V1, V2, V3, V4, I1, I2 and I3. Compare the results of the calculation with those from the experiments. Verify the Ohm s law for each resistor, KCL at each node and KVL at each loop. Verify that P=I 2 R=V 2 /R for each resistor. Show that the input power from source is equal to the sum of power dissipation on the individual resistors. What is the maximum value of voltage (V) if the power rating of each resistor is 0.25 W? Does KVL satisfy when the resistor value used is in Mega Ohm range (multimeter also has internal resistance in mega ohm range for voltage measurement) OR Does KCL satisfy when the resistor value used is in Ohm range (multimeter also has internal resistance in ohm range for current measurement)? NOTE: Submit Lab Sheet with report on next lab. Instructor s Signature Performance Date Submission Date Date