Series and Parallel Circuit Elements

Experiment 8: Series and Parallel Circuit Elements Laboratory Report Frenzyl Espinola, Anna Fermin, Loren Gabayeron, Kristal Fernandez Department of Math and Physics College of Science, University of Santo Tomas Espana, Manila Philippines Abstract The experiment is about the elements of series and parallel circuits. The laws on series and parallel resistors, as well as the color code for resistors were observed to calculate the total resistance. The proper connection for ammeter and voltmeter was also conducted and the readings for the voltage and current were obtained. 1. Introduction

The objectives of the experiment are to determine the resistance of a resistor based on its color code and to verify the laws on series and parallel resistors, as well as the cells. Some practical applications of these types of circuits are observable in our daily lives. An example of series circuit is the Christmas lights. If any one of the bulbs is missing or burned out, no current will flow and none of the lights will go on. On the other hand, an example of parallel circuits is the wiring system in our houses. If one of the lights burns out, current can still flow through the rest of the lights and appliances. . Theory Total Resistance: RT=VTIT Theoretical for series: RT = R1 + R2 Theoretically for parallel: RT=11R1+1R2 Internal Resistance of the cell: r= E-IRI Color Code for Resistors: AB X 10c + D Resistors for Series| Resistors for Parallel| RT = R1 + R2 + R3… | RT = 1R1+ 1R2+ 1R3| IT = I1 = I2| IT = I1 + I2| VT = V1 + V2| VT = V1 = V2| 3. Methodology Activity 1: Series Circuit Figure1: Experimental Set-up of Series Circuit The value of the two resistors used for this experiment was determined based on the color code. These are recorded as R1 and R2.

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The resistors, in series were connected to a dc source. The current and the voltage drop across each resister were measured using an ammeter and a voltmeter. Given the equation above, the total resistance was computed, as well as the theoretical resistance. The percent error was also computed. Activity 2: Parallel Circuit Figure2: Experimental Set-up for Parallel Circuit Same procedure as in activity one, but this time the resistors were connected in parallel. Total and theoretical resistance was also computed as well as the percent error. Activity 3: Internal Resistance of a Cell

Figure1: Experimental Set-up of Series By connecting a voltmeter across its terminals, the electron motive force of a cell was determined. A known resistance R was connected in series with the cell. By means of an ammeter, the current delivered to the circuit was measured. Using the given equation above, the internal resistance of the cell was solved. 4. Results and Discussion Table1. Series connection | Voltage (V)| Current (I)| R1 = 475-525| 2. 71| 0. 0054| R2 = 313. 5-346. 5| 1. 80| 0. 0054| Theoretical RT = 832. 64| Experimental RT = 820| % Error = 1. 52%| Table2. Parallel Connection Voltage (V)| Current (I)| R1 = 475-525| 4. 55| 0. 0175| R2 = 313. 5-346. 5| 4. 55| 0. 0175| Theoretical RT = 124. 625| Experimental RT = 124. 625| % Error = 0%| From Tables 1 and 2, we can infer that the laws are clearly observed from this experiment. In a series connection shown in Table 1, the total voltage resulted from the voltage from the first resistant plus the voltage from the second resistant. The current was also tested. Its current is just the same for all resistors. Total resistance from both the theoretical and experimental were calculated and obtained minimal percent error.

Table 2 shows the result from a parallel circuit. The voltage from the first resistance is equal to the second resistance. The current on the other hand, is differs from each resistant, and from the law, to get the total current, you must get the sum of these currents. The theoretical and experimental values for resistance were also calculated and yielded zero percent error. Table3. Internal Resistance of a Cell Electromotive Force of Cell (E)| 1. 4 V| Known Resistance (R)| 497| Current (I)| 0. 0026 A| Internal Resistance of cell (R)| . 537| The internal resistance of a battery determines its power life.

Any current in the battery must flow through the internal resistance. If there is a low resistance, the restriction for the battery to deliver the current would also be low. The internal resistance is in series with the voltage of the battery, thus the voltage of a battery actually decreases as the current drawn from it increases. Figure1. Electromotive Force of Cells 5. Conclusion In this experiment, to be able to determine the total resistance of the resistor, one can use the knowledge based on the resistor’s color code. A summary of the codes and its values, as well as the tolerance are given in the manual.

Another way of getting the resistance is by determining the voltage and current. Knowledge of the laws of series and parallel resistors will come in handy for one to successfully verify the resistance. This is proven by activities 1 and 2 wherein the resistances for both parallel and series circuits were obtained as well as the percent error. In addition, we can also conclude that a battery’s life or a cell depends on its internal resistance. This is what we obtained from Activity 3 wherein if there’s a high resistance, the restriction is also high, thus extending the battery’s life. 6. Applications . State the laws for series and parallel combination of resistances. Were these laws verified in you experiment? It is clearly seen in this experiment that in a series circuit, the current through each of the components is the same, and the voltage is the sum of the voltages across each component. On the other hand, in a parallel circuit, the voltage of the components is the same, and the total current is the sum of the currents through each component. 2. You have 4 identical resistors, each with resistance of 5 ohms. Determine all possible resistances that you may get using all four resistors.

For series, one can have a total of 20 ohms, provided with the equation of R= sum of all resistors. The parallel can only have 5 ohms of resistance given also the equation from the theory. 3. The human body is a god conductor, being almost 70% water. A wet dry skin has resistance as high as 104 – 106 ohms. However, when the skin is wet, the resistance drops to 1000 ohms or less. Why? Relate this fact in the operation of a lie detector. Most of the body’s resistance is in the skin; thus, the dead, dry cells of the epidermis are very poor conductors.

However, when the skin is wet, the resistance drops and the skin begins to be more of a conductor because of water, sweat and the presence of electrolytes. In line with this, in a lie detector, the activities of the body not easily controlled by the conscious mind. The body is subjected under different circumstances. Among these are sweating and release of more water. Notice that when we lie, or make something up, it takes us time to make an alibi or sometimes we get busted because we get too nervous and sweaty. 4. Compare the human circulatory system to an electric system.

The circulatory system is like the parallel circuits –the smaller blood vessels that branch off from an artery and then connect to a vein to return blood to the heart. An example of two wires, each as an artery and a vein, with some smaller wires connected between them. These smaller wires will have the same voltage applied to them, but different amounts of current flowing through them depending on the resistance of the individual wires. 5. Are household circuits normally wired in series or in parallel? Why? The household circuit is normally wired in a parallel circuit.

This is primarily because, when a system or a component goes down, the current, received will still be flowing and the supply of electricity wouldn’t stop for other appliances. A single electric power source supplies all the lights and appliances with the same voltage. However, if there is a short circuit, the voltage drops to almost zero, and the entire system goes down. 6. Discuss the working principle of ventricular defibrillator. Ventricular fibrillation is an electrical mechanism in cardiac arrest due to the electrical excitations of the chambers of the heart.

This would resort to the loss of coordinated contraction of the cells around the chambers. Because of malfunction in the proper contraction of the heart, it would no longer pump blood adequately or none at all. But by ventricular defibrillation, it gives treatment for this cardiac arrest. The device used is called a defibrillator. It consists of electrical energy and delivers this energy to the heart. The heart becomes depolarized, and the affected area of the heart muscle is cured.

Relating it to this experiment, a capacitor is charged with an appropriate level of voltage for the device. Upon initiation of the shock, current is delivered directly to the heart to interrupt the disordered heart rate and rhythm causing cardiac arrest and restore the heart’s normal conduction. 7. References Cutnell, D. & Johnson, K. (2010). Introduction to Physics. John Wiley and Sons Pte Ltd. Hoboken, NJ. (n. a). (2010). Ventricular Fibrillation. Retrieved last September 10, 2010 from http://emedicine. medscape. com/article/760832-overview

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