Ohms Law and Resistors in Series and in

Ohm's Law and Resistors in Series and in Parallel Presented by Mahmud Abdur. Rahman & Nazim Uddin Physics 2. 3 honor Class DR. Roman Kezerashvili

Objectives: 1. Verify law by observing the dependence of the electric current as a function of voltage and as a function of resistance. • 2. Determine the equivalent resistance of series and parallel combination of resistors and compare the results with theoretical predictions. • 3. Study currents flow and voltages in series and parallel circuits.

Equipment • 1 Resistance box • 2. Digital Multmeter • 3. DC power supply with adjustable voltage (0 -20 V) • 4. Resistors board • 5. Connecting wires • 6. Switch

Theory What is the Ohm’s Law • Ohm’s law States that current through a resistor is directly proportional to the applied voltage V and inversely proportional to the resistance R of the resistance • Ohm’s law is not a fundamental law of nature • An empirical relationship that is valid for certain material • at constant temperature Electric current I=Q/T Ohm’s Law I=V/R

Procedure • Part 1 • 1. Investigate the variation of the current with potential difference when the resistance is constant • 2. Investigate the variation of the current with resistance when the voltage is constant. • Part II • 1. Resistors in series • 2. Resistors in Parallel

Ohm’s Law( The relationship among current, voltage and resistance) Resistors in Series Resistors in Parallel Data: » Table 1. The Voltage Dependence of Current (Constant resistance) • Power supply , V • Voltage V, R 1= 1000 R 2= 1200 V Current I, A Voltage V, V • 4 4. 02 0. 0040 4. 02 0. 0033 • 5 5. 02 0. 0049 5. 02 0. 0041 • 6 6. 02 0. 0060 6. 03 0. 0049 • 7 7. 02 0. 0070 7. 04 0. 0058 • 8 8. 01 0. 0079 8. 01 0. 0066 • 9 9. 01 0. 0090 9. 00 0. 0074 10 10. 03 0. 0099 10. 02 0. 0082

Data • Resistance R, 1/R, -1 • 700 0. 00143 • 800 0. 00125 0. 01490 • 900 0. 00111 0. 01320 • 1000 0. 00100 0. 01190 • 1100 0. 00091 0. 01084 • 200 0. 00083 0. 00994 Current I, A 0. 01700 Voltage Power supply V, V=12 V from Slope, V 11. 874 %Difference 1. 06%

» Table 3. Resistors in Series Continuation • I = 0. 0024 A, V = 12 V, • Resistors Current I, A Voltage V, V Resistance R, • RA 0. 0024 8. 74 3620 • RB 0. 0024 2. 63 1090 • RC 0. 0024 0. 57 230 R = 4950 Equivalent resistance from equation (9) R = 4940 ; % difference = 0. 20% Total voltage from equation (5) % difference = 0. 50% V = 11. 94 V; – Table 4. Resistors in Parallel • I = 0. 032 A, • Resistors Current I, A Voltage V, V Resistance R, • RA 0. 0018 6 3620 • RB 0. 0054 6 1090 • RC 0. 026 6 230 V = 6 V, R = 185. 6

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Graph 2

Calculation and Analysis: 1. Use data from Table 1 and plot a graph of the current I us the voltage V for both values of the resistance. Determine the slope of the graph. From the slope of the graph find the resistance using » R=1/slope • and compare it to the actual value of resistance by calculating a percent difference. – 2. Use data from Table 2 and plot a graph of the current I versus the 1/R. Determine the slope of the graph. Compare the slope of the graph with the output voltage of power supply by computing a percent difference. – 3. Resistors in series. – Using the resistors value compute the equivalent resistance R of the circuit by using equation (9). Compare this value with your experimental measurement by finding a percent difference. – Using the measured voltages compute the total voltage V by using equation (5). Compare this value with your experimental measurement by finding a percent difference.

Continue Calculations

Continue Calculations

• According to the experiment we observed that the electric current through a resistor is directly proportional to the applied voltage and inversely proportional to the resistance of the resistor and verified Ohm’s law. • We also observed the difference between series and parallel connections. I LOVE PHYSICS THANKS TO PROFESSOR DR. ROMAN FOR MAKING PHYSICS SO ENJOYABLE