LAB REPORT ON SERIES AND PARALLEL CIRCUITS
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LAB REPORT ON SERIES AND PARALLEL CIRCUITS
TITLE: LAB REPORT ON SERIES AND PARALLEL CIRCUITS
STUDENT NAME:
COURSE:
INSTRSUCTOR:
Introduction
Background
Series and parallel circuits are the most fundamental concepts in any field dealing with electricity. The difference between series and parallel circuits arises where the path of the flow of current in the circuit is to be considered.
Series circuits
In a series circuit, for instance, the path available for the flow of current is only one and therefore any interruption of the conductivity of the circuit in one part will affect the flow of current to the rest of the circuit. A very simple example of such a circuit involves a connection of two bulbs to a battery, where, one terminal of the battery is connected to one terminal of the bulb. The other terminal of this bulb is then connected to one terminal of the second bulb and then the other terminal of this bulb is connected to the second terminal of the battery. Therefore, current flows from the battery to the first bulb, then to the second bulb and finally back to the battery.
In a series circuit, the current flowing through the components of the circuit while the voltage across each component is not the same since there is a voltage drop across each component as the current flows through it.
Therefore, in order to determine the current flowing through the circuit, we use the formula:
Where I, is the current, V the source voltage and RT is the total resistance in the circuit.
The voltage drop across each component can be obtained by:
Where I, is the current flowing through the circuit and R is the resistance of the individual component.
Parallel circuits
In a parallel circuit, there is more than one path that can provide for the flow of current. Therefore, interruption of one path does not affect the flow of current in another path. For example, considering two bulbs and a battery, a parallel connection involves connection of each bulb directly to the battery. Therefore, in such a case, each bulb is directly powered by the battery.
In a parallel connection, the voltage across the components of the circuit is the same while current is not the same. This is due to the fact that since there are many paths, current distributes itself to those parts such that the total current flowing through the circuit is obtained by addition of current in the individual path.
Therefore, in order to determine the current flowing through each path in the circuit, we use the formula:
Where I, is the current in a particular path, V the source voltage and R is the total resistance in that particular path. The voltage across each path is the same as the source voltage because of the direct connection to the battery.
Objectives
After the end of the lab, one had to be able to measure voltage current and resistance for DC series and parallel circuits, read a simple datasheet for a light emitting diode, design simple series circuits to light one LED and two LED’s, and, to be able to design a parallel circuit to light two LED’s.
Methods
Materials and tools used
The materials utilised in the lab included:
Breadboard: one breadboard was required to be used in this lab. A breadboard is a solder less board that has been designed and manufactured with contact points that can enable construction of a complete circuit without soldering by just inserting the components into the contact points.
Light emitting diodes
A light emitting diode is a semiconductor device consisting of a p-n junction which can emit light when current flows through the junction. Since it is a diode, it can allow current to flow in only one direction. It has two leads, the positive terminal and the negative terminal and this special diode will only allow current to pass through it if the voltage at the positive terminal is more than the voltage at the negative terminal by a certain value usually referred to as the forward voltage. For most LED’s this value range from 0.6V to 2.2 V. for silicon semiconductor diode, this value is usually 0.7V.
Resistors
Resistors of different values were also required. These include: 1KΩ, 2.2KΩ, 3.3KΩ and 6.8KΩ resistors
Potentiometer
A potentiometer was also required. With a potentiometer, we can obtain a range of resistances which depending on the value of the potentiometer. With a potentiometer, we eliminate the need for multiple resistors with different values as required in the lab.
Tools used
The tools used in the lab include: a digital multimeter (handheld and bench top) as well as the DC power supply
Procedures
Part 1: Resistors in series, Resistor in parallel
Resistors in series
1) First, we explored how to measure the resistance of resistors in series using the breadboard. We took 4 resistors and measured their individual resistance values using the DMM. One end of the first resistor was placed into a contact point. We then placed one end of the second resistor into the same node as the first resistor then placed the other end into another contact point. We continued chaining the resistors until all 4 were connected and then measured their combined resistance.
2) A voltage was then added across all the resistors. We used the traces that run down a column for the power supply. The free end of the first resistor was then placed into a contact point in one of the column traces. We then placed the free end of the fourth resistor into a contact point in a different column. The DC power supply was then connected to the appropriate columns, and the power supply turned on and set to a low voltage.
3) We then measured the current through the circuit.
4) We then measured the voltage across each of the four resistors.
5) By doing some calculations, I was able to demonstrate that the sum of voltages across the four resistors is equal to the voltage supplied by the DC power supply.
6) Also, by multiplying the power supplied by a factor of two, I was able to demonstrate that the voltage drop across each of the resistors responds proportionally.
Resistor in parallel
1) We then took then 1 KΩ, 2.2 KΩ, 3.3 KΩ, and 6.8KΩ resistors and measured their actual resistance using the DMM again and then placed the four resistors in the breadboard so that they were connected in parallel. We then measured the total resistance of the four resistors in parallel.
2) We then Connected the DC Power Supply to the parallel circuit and set it to 5V and measured the voltages across each resistor. I then used the current divider rule to calculate the expected source current and the current flowing through each resistor. We then measured the source current and the current through each resistor and recorded the details in a table.
3) By doing some calculations, I was able to demonstrate that the sum of currents through the four resistors is equal to the current supplied by the DC power supply (Kirchhoff’s Current Law).
4) Also, by multiplying the power supplied by a factor of two, I was able to demonstrate that the currents through each of the resistors respond proportionally.
Part 2
Series Circuit to light 1 LED
1) We came up with a simple LED circuit.
2) After looking up for the forward voltage and the characteristic forward current for the LED, and using a 5V supply I was able to determine the value of the current limiting resistor to be used in the circuit.
3) We found a current limiting resistor with a value close to the calculated one and connected the LED and resistor in series and connected the circuit with the columns in the breadboard with power and ground and turned on the power supply setting the voltage at 5V.
4) We then switched the order of the LED and resistor and observed any change in the circuit
5) We then first estimated the forward voltage and then measured voltage across the LED. By slowly decreasing the power supply voltage until the LED was off, we then measured and recorded the voltage at this point.
6) A potentiometer was then connected in series with the resistor and LED and its resistance varied. We observed the changes to the LED
Series Circuit to light 2 LED’s
By adding another LED to the circuit, we calculated the value of resistor needed such that the current through the circuit was 20mA and voltage drop across the diode equal to forward voltage and built the circuit on the breadboard. We then measured the voltage drop across the each diode and the resistor and also the current through the system. I was then able to calculate the power dissipated by the each of the two diodes and the resistor as well as the power generated by the DC power supply
Parallel Circuit to light 2 LED’s
- We came up with a parallel circuit and determined the resistor values for the resistors to be connected in series with each LED in each of the branches, and built the circuit on a breadboard. We then measured the current through each branch, and the voltage drop across the two diodes and the two resistors in the circuit. I was then able to calculate the power dissipated by the diode and resistors and the power generated by the power supply.
- We then tried a different connection of a parallel circuit. This was achieved by connecting the two diodes in parallel and then placing a resistor in parallel with the two diodes. We built this circuit by first determining the value needed for the resistor and then measured the current through the two diodes and the resistor as well as the voltage across them. I then calculated the power dissipated by each element and total power supplied.
- I then compared the three different circuits in terms of power dissipation, in terms battery life if the battery was to be replaced with an equivalent one with a specific ampere hour rating and in terms of what would happen if one of the LED’s were to burn out.
Results
Discussion
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