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Ohm’s law & resistors in parallel & in series Essay

Our object is to confirm Ohm’s law by analyzing the dependence of the electrical current as a function of voltage and as a function of resistance. Also, we studied the current flow and voltage in series and parallel. Finally, the lab determined the equivalence resistance of series and parallel combination of resistors and compared the results with theoretical data.

Theoretical Background:
The first thing that needs to be described in this lab is what the electric current I: I =. The electric current is defined as charge over time and the unit is ampere (A). In a case where we have the voltage, resistance and current we can set the equation for resistance to be; R = where the unit is called Ohm (Ω). “The current through a resistor is directly proportional to the applied voltage V and inversely proportional to the resistance” (College Physics Laboratory Experiments, 43) in our lab experiment we used some machinery to produce and to measure voltage and some current. We were then able to find its resistance. These apparatus are called ammeter which displays the amount of current in circuit, and the voltmeter to read the voltage (potential difference). Reminding that this diagram is named circuit and V is applied across the ends of the metallic conductors.

The second part of our lab was dedicated to find the resistance in the resistors both in parallel and in series. The formula to find the resistance through series is fairly easy; it looks a lot like the formula in series for conductors. It’s basically RA+RB+RC = Req. When it comes to find the total resistance when the resistors are in parallel we add the reciprocal of the combination of resistors. It will look like this; + + =

Part 1: Verification of Ohm’s Law
1 Investigate the variation of the current with potential difference when the resistance is constant. a Set up the circuit as shown in Fig 4.2 and chose the resistance of the variable resistor box of R = 1000 Ω. Set the ammeter to the range of mA and the voltmeter across the resistor the range of 25V. b After the instructor has checked the circuits, turn on the power supply. c Vary the output voltage of the power supply from 4 V to 10 V in the increment of 1 V and record the readings of the voltage V across the resistor and the corresponding current I through the resistor in Table 1. d Using the same circuit setup, set resistance of the variable resistor box to R = 1200Ω and repeat the steps 2 and 3. 2 Investigate the variation of the current with resistance when the voltage is constant. a Use the same circuit setup and set the output voltage of power supply to 12V. b By keeping the output voltage of the power supply constant, vary the resistance of the resistor box from 700 Ω to 1700 Ω in increments of 200 Ω. Record values of the current I through the resistor and the corresponding resistance R in table2.

Attached to report.


1 Use the data from table 1 to plot a graph of current Vs. voltage for both values of the resistance. Determine the slope of the graph. From the slope of the graph find the resistance using: a) R = R = R =1000 Ω

% diff = = 0%

b) R = R = R =1250 Ω

c) Slope = 12.7
V = 12 v


1. Does your resistance follow Ohm’s law? Base your answer on your experimental data. The resistance does closely follow Ohm’s law because when using the data mathematically it is closely related to the resistance present in the data.

2. A typical color television draws about 2.5 A when connected a 120V source. What is the effective resistance of the TV set? I = , R = = = 48 Ω

3. Explain the difference between series and parallel connections. In a series circuit the charge is 1/Q + 2/Q + while in a parallel connection, the charge is added to the total voltage.

4. Does your experiment present evidence that the current divides in a parallel circuit?

5. From your experimental observations of a series circuit, what relationship do you find between the voltages across the individual resistance and voltage across the entire series group? The voltage in a series compared to parallel is much lower

6. From your experimental observations of a series circuit, what relationship do you find between the voltages across the individual resistance and current flow across the entire series network?
The resistance is constant.



Our results for both parts of this lab demonstrated the relationship outlined by Ohm’s Law and fostered a higher comprehension of the mechanisms driving circuit behavior. The direct relationships between voltage, current, and resistance allow measurements of the voltage and current without resistance being known. Additionally, the ability to manipulate voltage allowed the experiment to contain a sense of systematic collection of data to provide a contextual experimental example of the relationships in Ohm’s law. Moreover, the experiment also demonstrated how the different are configurations of resistors, parallel.

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