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Bulbs in Series and Parallel

Bulbs in Series and Parallel

Introduction: (Initial Observation)

Have you ever wondered what happens if you try to light up two lamps (light bulbs) with one battery? How do you connect them? How many different ways you may connect two lamps to one battery? Does the connection arrangement affect the amount of light in each lamp?

If you can modify the amount of electricity available to each lamp, you will be able to adjust the amount of light and you can safely use a strong battery to light up many low voltage lamp.

In this project you will make models of series and parallel circuits and use them to find answers to your questions. You can also take your model to the classroom and show other students how you can change the distribution of electricity by connecting components in series or in parallel.


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 electricity, voltage, and current. Read books, magazines or ask professionals who might know in order to learn how the connecting circuits affect the distribution of electricity among different devices. Keep track of where you got your information from. Following are samples of information you may find:

What is electricity? Electricity is the flow of electrons in a conductor such as a copper wire. (It is almost like the flow of water in a pipe. In order for water to flow from one side to the other side, there must be some excess pressure in one side.

What is voltage? Voltage is the difference in pressure or concentration of electrons between two points. Open the water faucet and try to stop water with your hand. You will see that the pressure is high. That is the pressure that makes water to come out at a high speed. When talking about electricity, that pressure is known as voltage.

What is current? Current the amount of electrons flowing per second. Think of a wide river. Although the water moves slowly, a large amount of water is passing you every second. Now thing of a water hose you use to water your garden. Although the water is moving very fast inside the hose, the total amount of water passing one point of the hose is not very large. It may take you days to fill up a pool with one hose; while the slow flow of water in a large river may fill up the same pool in a few seconds. So the water current is high in a river, but the water current is low in a hose.

What is a load? A load or a resistor is anything that consume electricity. For example a lamp in an electrical circuit is a load.

What is a parallel circuit? A parallel circuit has more than one resistor (anything that uses electricity to do work) and gets its name from having multiple (parallel) paths to move along . Charges can move through any of several paths. If one of the items in the circuit is broken then no charge will move through that path, but other paths will continue to have charges flow through them. Parallel circuits are found in most household electrical wiring. This is done so that lights don’t stop working just because you turned your TV off.

What is a series circuit?

Series circuits are sometimes called current-coupled or daisy chain-coupled. The current that flows in a series circuit has to flow through every component in the circuit. Therefore, all of the components in a series connection carry the same current.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

How does a series circuit affect the distribution of electricity among different loads?

How does a parallel circuit affect the distribution of electricity among different loads?

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1: Series Circuits

Introduction: In this experiment you will construct a series circuit and examine the effect of serial connection on the distribution of electricity.


  1. Mount 5 miniature bases and a battery on a wooden board.
  2. Connect all miniature bases together in a chain using copper wires.
  3. Connect a copper wire from the positive (+) pole of the battery to the open connection of the miniature base in one end of the chain.

4. Label other connections from A to E as shown in the diagram.
5. Connect another copper wire (shown red) to the negative end of the battery. The other end of this wire will remain open.
6. Mount or screw one lamp in each screw base.
7. Use the open wire and touch the connection screws in positions A, B, C, D and E. Observe how does the amount of light change when you increase the number of lamps in circuit. Record your observations. Also note:
_When you touch the connection A, only 1 lamp will be in your series circuit.
_When you touch the connection B, 2 lamps will be in your series circuit.
_When you touch the connection C, 3 lamps will be in your series circuit.
_When you touch the connection D, 4 lamps will be in your series circuit.
_When you touch the connection E, 5 lamps will be in your series circuit.
8. Permanently connect the open wire (shown red) to the last connection screw labeled E. (If you are getting no light, switch to connection D or C until you see some light).
9. Unscrew one of the lamps in circuit. How does this affect other lamps in the series circuit?

With this experiment you can verify that removing one of the lamps of the circuit, the other lamp fades instantly. This happens because the lamps in the circuit are disposed in serial. In an electric circuit, the electrons move from the positive pole (+) to the negative pole (-). When removing one of the lamps out of the support, the electrons flow in the string is stopped. That can be compared to traffic in a freeway. Imagine that a certain freeway, that connects city A and B, is closed and that this connection road is the only one available. It would cause no possible connection between the two cities because the cars were not allowed to circulate. The same way, in the present experiment, the electrons in the serial circuit only have a way to flow. If it is closed, the electric current becomes zero. In other words, the lamps fade because there are no electrons flowing in the circuit.
In the serial circuits several rules exist for qualitative and quantitative analysis. The current intensity in this circuit type is the same for the two lamps (resistances). On the other hand, the total resistance is equal to the sum of the resistance of each lamp. The potential is equal to the sum of the potential applied in each lamp (resistance). The electric system in your house has resistances that are associated in serial and parallel.

Additional information about Series Circuits

In a series circuit if you follow the circuit diagram from one side of the cell to the other, you should pass through all the different components, one after the other, without any branches.

Make a series circuit similar to the diagram in the right. Start with two light bulbs, test the circuit, observe the amount of light and then increase the light bulbs to three and four.

Does the amount of light change when you increase the number of light bulb in a series circuit?

Now unscrew one of the light bulbs. What happens to the other bulbs?




In a series circuit, if a lamp ‘blows’ or a component is disconnected, all the components stop working.

If you put more lamps into a series circuit, the lamps will be dimmer than before.


Series circuits are useful if you want a warning that one of the components in the circuit has failed. They also use less wiring than parallel circuits (see below).



Experiment 2: Parallel Circuits

Introduction: In this experiment you will construct a parallel circuit and examine the effect of parallel connection on the distribution of electricity.


  1. Mount 5 miniature bases and a battery on a wooden board.
  2. Connect one contact screw of each miniature base to a copper wire that is connected to the positive pole of the battery.
  3. Connect the remaining contact screw of each miniature base to a copper wire that is connected to the negative pole of the battery.
  4. Mount or screw one lamp in each of the miniature bases.
  5. As you add the lamps, compare the amount of light on each lamp. Do you see any noticeable change?
  6. Unscrew one of the lamps in circuit. How does this affect other lights in the parallel circuit?

In contrast with the serial circuit, if we remove a lamp of the support, the other lamp doesn’t fade. As always, the electrons flow from the (+) to the (-) pole. When we remove the lamp of one of the supports, the electrons don’t move in that branch of the circuit. However, that doesn’t implicate that the circuit is closed because the electrons have an alternative way (other branch).
As well as in the serial circuit, for the parallel circuit type there exists several rules for the quantification of the resistance, potential and current intensity. The potential is the same in the two lamps because we have two independent branches. The inverse of the total resistance is equal to the sum of the inverse of the located resistances in the circuit (lamps). In the particular case of the current intensity, this is equal to the sum of the current intensities that pass in each one of the branches.

Additional information about

Parallel Circuits

The tracks on railway lines run side by side in parallel. A parallel circuit is similar. The different components are connected on different wires. If you follow the circuit diagram from one side of the cell to the other, you can only pass through all the different components if you follow the branches.

A parallel circuit with one cell and two lamps

In a parallel circuit, if a lamp ‘blows’ or a component is disconnected from one parallel wire, the components on different wires keep working. Unlike a series circuit, the lamps stay bright if you add more lamps in parallel.

In a parallel circuit with lamps on separate wires, if one breaks the other stays lit

Parallel circuits are useful if you want everything to work, even if one component has failed. This is why our homes are wired up with parallel circuits.

Materials and Equipment:

Materials you need for this project include:

  • 2 Batteries (1.5-volt or 6-volt)
  • 2 Wood boards (One for parallel and one for series circuit)
  • 10 lamps/ Light Bulbs (1.5-volt or 6-volt, depending on your battery)
  • 10 miniature bases or lamp supports
  • Copper Wire
  • 2 Switches or Knife switches (optional: If you use a switch, you must install it between the battery and your circuit.)
  • Lid wires with alligator clips
  • Electric Motor (if necessary)

Where to Buy?

If you don’t know any local store that sell the above items, you may order them from http://shop.MiniScience.com

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.

Your results will include your display, your demonstration and what you learned during your experiments.


No calculations are required for this project.

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.


List your online references or books as your bibliography.