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Electric Circuits Factors affecting voltage, amperage, resistance

Electric Circuits- factors affecting voltage, amperage, resistance

Introduction: (Initial Observation)

In a closed electric circuit, resistance of the components and the voltage of power source are affecting the electric current. Current is the rate of flow of electrons. Knowing how these conditions can change, is the key to designing and building any electric circuit. For example suppose that your power source or battery output is 12 volts and the only type of light bulbs that you have access to are designed for 3 volts. How can you reduce the voltage of your battery to match your light bulbs?

(Remember that a 3 volts bulb will blow up instantly if you connect it to 12 volts battery.)

In this project you will experiment different electric circuits in order to find out the factors that affect the voltage, resistance and electric current.


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

Information Gathering:

Find out about electric circuits and factors that affect the flow of electrons in the components of an electric circuit. Read books, magazines or ask professionals who might know in order to learn about voltage, resistance and electric current. Keep track of where you got your information from.

It can be very easy to learn about electricity if you compare it to a water system with pipes, pumps, tanks and valves. Battery is basically like a water tank. Wires are like pipes, switches are like valves and light bulbs are like water filters (resistance) and electric motors and electromagnets are like water turbines. With this analogy every condition of an electric circuit can be compared with a water system to conclude the outcome of any change in values or design.

Some Basic Information:

It is probably safe to assume that everyone reading this page has come into contact with a flashlight. Have you ever taken a flashlight apart? Not just to replace the batteries, but to investigate every part of the flashlight? The flashlight is not a very complicated device. What parts are used to make up a flashlight? Basically, there are three main components. The batteries, which supply the energy to power the flashlight, are the main component. The light bulb, which illuminates when current is passed through it, is the next major component. The connecting structure, which might consist of copper bands and a switch, help connect or disconnect the power source (battery) from the load (light bulb).

In many engineering fields, it is convenient to develop a language for communicating information and ideas. Electrical circuits is no different. In electrical circuits, the electrical devices are not drawn pictorially, but instead they are drawn schematically. Thus, a diagram can be drawn that schematically captures the main essence of the flashlight’s operating principles. Because the flashlight is such a simple device, its schematic diagram should be easy to follow or understand. For some introduction to electricity and some schematic symbols, visit http://www.electronicstheory.com/html/e101-1.htm or if you just want to see some symbols, visit http://webhome.idirect.com/~jadams/electronics/schem.htm.

Once a schematic diagram is available, how can one analyze the system? First, we should point out that we will frequently refer to diagrams like Figure 2-3 as a circuit. A circuit is simply an interconnection of electrical components, e.g., a source and a load in the flashlight circuit. The interconnections are made with lines, which represent wires or metal busses, in an electrical circuit. Electrical circuits make it more convenient to analyze electrical devices versus elaborate sketches of the physical devices. However, as you work through this module, you should try to mentally picture the true physical system that is being represented by the electrical circuit or schematic diagram. You will actually become a better problem solver if you are able to establish a connection between physical systems and the more academic circuit diagrams used for analysis.

What can we deduce about the flashlight circuit based on our understanding of watts, voltage, and current from the Introduction? The batteries allow us to get a handle on the voltage being supplied in the circuit. If we have two 1.5 volt batteries connected end-to-end (in series), then the supply voltage in our circuit should be about 3 volts. What else do we know or can we learn by examining the component parts of the flashlight system more closely? If we look very carefully at the light bulb, it may be possible to gather more data on this component of the flashlight circuit. For example, a very small flashlight had a light bulb with the following information imprinted on its side: 2.2 Volts and 0.25 Amps. Thus, the light bulb must like to operate with 2.2 volts across it and 0.25 amps flowing through it. The light bulb can then be modeled by a circuit element that has 0.25 amps of current flowing through it when 2.2 volts are dropped across the device. As we will learn in the next section, a device that has these properties is a resistor. For analysis purposes, we can replace the schematic representation of the light bulb with the schematic symbol for a resistor and create a new electrical circuit that models the same flashlight system as in Figure 2-3.

Motivated by the electric circuit model of a simple flashlight system, the next section will investigate the current and voltage relationship of a resistor (Ohm’s Law) and provide an equation for determining the resistance associated with a given resistors.

Ohm’s Law and Resistance


As we saw on the previous page, in order to have a current flow then we must have both of the following:

    1. A source of voltage, such as a battery
    2. A path for the electrons to follow.

When they are put together we have a circuit.


Look at the picture to the right which shows a simple circuit of a battery connected to a light bulb. We have a voltage source (the battery) and a path for the electrons to follow (through the light bulb). The question remains, “How much current is flowing through the light bulb?” In order to answer this question we shall first have to introduce the concept of resistance.

The common symbol for a resistor

You might think that the current is determined by the voltage (and to a certain extent it is). Indeed many people think the voltage is the current, which it is not. The current is the flow of electrons, and is driven by the voltage, but the circuit through which the electrons flow also plays a part in determining the current. We can see this by going back to out water analogy. Suppose that I had two hosepipes, one of diameter ½” and one of diameter ¾”, both connected to the same faucet. They would then have the same water pressure. However, if we measure the flow rate through the two hosepipes we will find that the larger diameter pipe has a higher flow rate (see the activates section).

A battery connected to two circuits.

The same concept applies to electrical circuits. If we have two circuits connected to the same battery the currents might will be different. Although the voltage is the same for each, current might be able to flow more easily in one circuit than in the other. We say that the have different resistances. The circuit with the lower resistance to current flow will have the larger current flowing through it.

Ohm’s Law

The relationship between the current flowing in a circuit, the voltage which drives the current, and the resistance of the circuit to current flow is expressed by Ohm’s Law

Voltage = Current x Resistance

Since voltage is measured in volts and current in amps, the units of resistance should be volts per amp. This is commonly written as ohms, and given the symbol W.

An Example

Suppose that we connect a light bulb with a resistance of 30 W to a car battery (voltage 12 V). What is the current which flows through the battery?

From Ohm’s Law, with voltage = 12 V for a car battery, and resistance = 30 W

12 = Current x 30

Current = 12/30 = 0.4 A

Question/ Purpose:

The purpose of this project is to understand the relation between Voltage, Resistance and Current. We are trying to find answers to the following questions.

    1. What is the relation between voltage, resistance and current? OR How do voltage and resistance affect the current in an electric circuit?
    2. How can we increase or decrease the voltage?
    3. How can we increase or decrease the resistance?
    4. what factors affect the electric current?
    5. What electrical specifications should we know about an electric appliance.

Only the first question is the main question for this project. All others are helpful but optional questions that you may find an answer to.

Identify Variables:

Variables that may affect the function of an electric circuit are Voltage, Resistance, current and the design of the circuit. We will study the effect of all these variables on each other and on the general function of an electric circuit.

Another way of identifying variables is:

Voltage and Resistance between two points in an electric circuit are independent variables. Any change in voltage and resistance may result a change in the electric current. Current is our dependent variable.


My hypothesis is that each electrical device has it’s own resistance that can not be affected by any other factor. Also each device is designed for a specific voltage. Excess voltage will cause extra electric current and may cause overheat, fire and damage to that device.

Another possible hypothesis:

My hypothesis is that any decrease in resistance or increase in voltage can increase the current. My hypothesis is based on my analogy of comparing electric current (flow of electrons) with water current (flow of water). Less resistance in a water passage will cause a higher rate of flow. Also more water pressure will cause a higher rate of water flow.

Additional hypothesis for questions 2 to 5 are offered in the experiment section.

Experiment Design:

Experiment 1:

In this experiment we modify the voltage to see how current will be affected by changes in the voltage. We use a 6 volts light bulb as a resistance. We measure it’s resistance using a multimeter before connecting it to the circuit.

Material and equipment:

    1. Multi-meter (Analog or digital)
    2. 6 volts miniature light bulb with a miniature base
    3. Four 1.5 volt flashlight batteries (AA, C or D size)
    4. One 6 Volt battery (Known as lantern battery)
    5. One 9 volt battery
    6. A wooden base to mount the circuit
    7. Some insulated wires (Ask for thermostat wire)
    8. Additional material such as metal plates, screws, glue, tape


    1. Set the multimeter to measure the resistance. Measure the resistance of the light bulb before connecting it to the circuit. Record it as the resistance. How many ohms is the resistance of the light bulb?
    2. Set the multimeter to measure voltage and then measure the voltage of your batteries. Record the results.
    3. Set the multimeter to measure the electric current. Connect the multimeter, 1.5 volt battery and the light bulb all in a circle circuit. Record the electric current. How many amperes is the current?
    4. Replace the 1.5 volt battery with a 6 volt battery and measure the current again. Do you see any difference on the amount of light in the bulb?
    5. Replace the 6 volt battery with a 9 volt battery and measure the current again. Do you see any difference on the amount of light in the bulb? Did you blow up the bulb because you applied excess voltage to it?
    6. Write the result of your experiments in the following table.

This is just a sample table. Values are not real. Write your own values.

Voltage (volts) Resistor Value (ohms) Current (amps)
1.50 V 6.6 ohms 0.22 A
6.00 V 6.6 ohms 0.90 A
9.00 V 6.6 ohms 1.36 A

For more accurate results in the above experiments, you must measure the voltage between two ends of the light bulb while the circuit is closed and the light bulb is on. This requires having two multi-meters. One as an ammeter in the circuit and the other as a voltmeter across the light bulb. If you have only one multi-meter, you can perform the test twice! Measure the current once and measure the voltage the second time. This is important to be done because weak, low quality and old batteries will show a high voltage while they are not connected to a circuit, but their voltage will drop as soon as you connect them to a load such as a light bulb.

What is the relation between the values in your table? Does current increase when you increase the voltage? How much does the current increase when you double the voltage?

More details:

A simple electric circuit may contain a battery, a light bulb and the connecting wires. In such circuit we don’t know what is the voltage across the light bulb and we don’t know how many amperes is the electric current.

Although you may know that you are using a 6 volt battery, you cannot be sure that the voltage across the light bulb is 6 volts; the voltage in many batteries drop when you place them in a circuit. This condition mostly happens in small batteries.

To measure the current in a circuit, you must place the ammeter in the circuit. In other words the electricity at some point enters the ammeter and exits the other side. This method of placing a device in a circuit is called connection in series. Ammeters always must be installed in series.

Most multimeters can be used as an ammeter too. You just need to change the knob and set it to Amperes; you also need to change the position of wires. Usually the red wire of a multimeter must be inserted to another hole when you want to measure current. See the reference manual of your multimeter for details.

Ammeter = Ampere meter


To make sure that you will measure and report the correct voltage you must have a second multimeter or voltmeter and connect it parallel to the light bulb (as shown in the diagram).
In this way you will be able to read both the voltage and the current at the same time.

Make a graph:

You can make a bar graph to visually present your results. Make one vertical bar for each voltage. To name the bars, write the voltages under the bars. The height of each bar will be the current you observe/read on your meter.

Experiment 2:

The purpose of this experiment is to see how can we increase the voltage. My hypothesis for this question is that we can connect multiple batteries in series to create a higher voltage. My hypothesis is based on my observation of flashlights that have four 1.5 volt batteries but they use a 6 volts light bulb. If you have four 1.5 volt batteries, connect two of those in a series and see what will be the total voltage. Connect 3 or 4 batteries in a series and measure the voltage again. Record the results.

1.5 Volts
3 Volts
4.5 Volts
6 Volts

Use one, two, three and four 1.5 volt batteries to create 1.5, 3, 4.5 and 6 volt power sources and repeat the experiment 1 again and record the results in a table like this.

Voltage (volts) Resistor Value (ohms) Current (amps)
1.50 V 6.6 ohms
3.00 V 6.6 ohms
4.50 V 6.6 ohms
6.00 V 6.6 ohms

Make a graph:

You can make a bar graph to visually present your results. Make one vertical bar for each voltage. To name the bars, write the voltages under the bars. The height of each bar will be the current you observe/read on your meter.

Experiment 3:

The purpose of this experiment is to see how can we increase the resistance? My hypothesis for this question is that by connecting multiple resistors in a series we can increase the resistance. That is like having a series of stop signs and traffic jams in a road that can add together and cause a more serious traffic problem. Also I think by connecting resistors parallel to each other, we can reduce the resistance. This is like having some side streets. that can reduce the traffic jam problem.


    1. Measure the resistance of a 6 volts light bulb and record the result.
    2. Connect two light bulbs in a series and measure the total resistance and record the result.
    3. Connect tow light bulbs parallel to each other and measure the resistance again. and record the result in a table like this:
Combination Picture and diagram Resistance (ohms)
Single light bulb
Two light bulbs in series
Two light bulbs in parallel

Experiment 4:

Find 10 electrical appliances around the house and determine their voltage, current, and power requirements.

Identify 5 different electrical devices in an automobile.

Experiment 5:

The purpose of this experiment is to see how can we reduce the voltage. My hypothesis is that resistors can be used to reduce the voltage.


Connect two bulbs in series and place them in a circuit with a battery. Measure the voltage on two ends of the battery. Measure the voltage on two sides of each light bulb. Record the results, analyze it and write your conclusion.

Additional Experiments:

You can design many additional experiments for this project. If you like to do so, discuss your idea with your project advisor.

Materials and Equipment:

List of material can be extracted from the experiment section.
To purchase online, you may try www.klk.com and MiniScience.com online store.

To purchase locally, please try your local hardware store.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.


If you do any calculations, write your calculations in your report. Among the calculations that you may do is using the Ohms Law formula of V=I.R and see if the results of your experiments will match this formula. If it does not match, can you find an explanation for the differences.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.


Visit your local library and find books related to electricity and electrical circuits. Review the related sections and list them as your references. This is how you may list your references:

    • Basic Electricity (Book) by Van Valkenburg
    • Basic Electricity (Book) by Bureau of Naval Personnel
    • Basic Electricity: A Self-Teaching Guide (Wiley Self-Teaching Guides)
      by Charles Ryan
    • Delmar’s Standard Textbook of Electricity, 3E (Hardcover)
      by Stephen L. Herman

You may also have some web based references including ScienceProject.com. Following are some we based references:

Introduction to Electricity: http://www.ndt-ed.org/EducationResources/HighSchool/Electricity/electricityintro.htm

Introduction to electricity and batteries (Video) http://video.google.com/videoplay?docid=-110952566405373011

Additional Workout

Problem (Part A):
How many ways can you arrange a battery, one wire, and one flashlight bulb to make the bulb light?

Gather these materials:
1. One dry cell (size D)
2. One bare, uncoated copper wire
3. One flashlight bulb
4. Paper for diagramming

Procedure (Part A):
1. Arrange the materials in as many ways as you can so that the bulb lights.
2. Make a sketch of each set-up. Include sketches of failures as well as successes.

Think it over:
In your own words, describe the similarities between your successful trials.

Problem (Part B):
How do various arrangements of batteries and bulbs affect bulb brightness?

Gather these materials:
1. Two dry cells (Size D)
(If you do not have access to flashlight bulbs and bulb holders, you can use the bulbs and bulb holders from a set of miniature tree lights. Just cut the wires between bulbs. Size D dry cells will light these tree lights.)
2. Flashlight bulbs
3. Wires
4. Bulb holders

Procedure (Part B):
1. Using one battery, light as many bulbs as you can. Keep track of your trials through your sketches.
2. Using two batteries, light as many bulbs as you can. Again keep track of your various arrangements of materials.
3. Using three bulbs and two batteries, discover arrangements that give different degrees of bulb brightness. Keep a record of your trials.

Think it over:
1. How did you make the most lights glow using only one battery? Compare results with class.
2. What set-up lit the most lights when you used two batteries? Compare results with the rest of the class.
3.How many different degrees of brightness did you obtain using three bulbs and two batteries? Compare results with class.

Problem (Part C):
How many different ways can you connect bulbs and batteries and still have a working circuit?

Gather these materials:
1. Bulbs
2. Sockets
3. Batteries and wire (Size D)
4. Battery holders

A shorthand notation for drawing circuits is very convenient when studying and comparing circuits. Circuit symbols for a light bulb, bulb holder, a battery, and wire appear in order below.

1. Connect the materials as shown in the circuit diagrams.

Do each of these circuits work?
These bulbs are connected in series.

2. Using the second diagram unscrew one of the bulbs. What happens?

3. Set up the materials as shown in the following diagram.

These bulbs are connected in parallel.

4. Unscrew one of the bulbs. What happens?

Think it over:
1. Build a circuit using two batteries and one bulb in which the batteries are connected in series. In parallel. Sketch your circuits.
2. In your own words describe the differences between series and parallel circuits.

Circuit Circus

1. Using bulbs, wires and batteries, you will make a complete electric circuit.
2. You will use symbols to illustrate and compare circuits they construct.
3. Using bulbs, wires, and batteries, you will make series and parallel circuits.

A circuit is a path for electric energy to follow. Without a complete path, no energy flows and bulbs will not light. You will learn that both ends of a battery must be involved in a complete circuit. Use science books and reference books to gain a greater understanding of electric circuits if you feel your background knowledge is limited.
Houses are wired in parallel so that other parts of a circuit continue to work even if one appliance or light bulb fail. Houses and other buildings have many circuits in them, and these circuits are protected by fuses or circuit breakers. Too many appliances on one circuit will draw too much current, which in turn can melt insulation and cause a fire. Fuses and circuit breakers are designed to open the circuit before overheating takes place.

Size D batteries
Bare copper wire, insulated wires, or foil ribbons
Flashlight bulbs and bulb sockets
Battery holders

(NOTE: If you do not have bulbs and bulb holders, do not despair. Miniature tree lights will work well in this activity. All you have to do is cut the wires between lights on a string of tree lights. While there may seem to be lots of wire, each bulb holder has only one wire in and one wire out. You can use these bulbs and wires with the batteries. About one inch of insulation needs to be stripped off the end of each wire. Also, wide rubber bands stretched around the length of the battery serve as battery holders and will hold wires in place on the + and – ends.)