ohm's law light bulb experiment

FREE K-12 standards-aligned STEM

curriculum for educators everywhere!

Find more at TeachEngineering.org .

• TeachEngineering
• Ohm's Law I

Hands-on Activity Ohm's Law I

Grade Level: 10 (9-12)

Time Required: 3 hours

$3 is for light bulbs; the rest of the materials are available in most school classrooms

Group Size: 3

Activity Dependency: None

Subject Areas: Physics, Science and Technology

TE Newsletter

Engineering connection, learning objectives, materials list, worksheets and attachments, more curriculum like this, pre-req knowledge, introduction/motivation, vocabulary/definitions, investigating questions, troubleshooting tips, activity extensions, user comments & tips.

Ohm's law is the basis of all electrical systems. Electrical engineers use this equation to guide the design of electrical systems. Students need a strong foundation in Ohm's law while designing circuits on their own.

Application of the following:

• series/parallel circuits (ways to connect them and have an effect on V and I)
• circuit components
• devices that can be used to measure voltage and current

Educational Standards Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards. All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN) , a project of D2L (www.achievementstandards.org). In the ASN, standards are hierarchically structured: first by source; e.g. , by state; within source by type; e.g. , science or mathematics; within type by subtype, then by grade, etc .

International technology and engineering educators association - technology.

View aligned curriculum

Do you agree with this alignment? Thanks for your feedback!

State Standards

Hawaii - science, massachusetts - science.

Each group needs:

• 1 6.3V light bulb
• 1 lamp base
• 3 AA battery holders (including wires)
• 5 alligator clips
• two 1.5 volt batteries and/or power supply
• Ohm's Law Data Sheet
• Before beginning this activity, introduce students to electricity, current, voltage, resistance and Ohm's law.
• The functions and structures of circuit components such as conductors, loads and controllers should be discussed, and those existing in the circuit should be identified during the activity.
• Brief discussion of the structure of light bulbs, as well as batteries may also be included.
• (optional) Make sure students are familiar with the provided materials (wires, batteries, light bulbs, multimeter [see How to Use a Multimeter ] etc.), as well as safety precautions when working with different forms of electricity.

Where would we be today without electricity? Though we may not think about it often, our lives revolve around electricity – we depend upon it for light, heat, communication, entertainment and even healthcare. This power can not only be derived in the way we usually think about it – through power lines to our homes, schools and places of work – but also through self-contained power sources such as batteries. Since batteries are only able to provide a set amount of voltage (for example, a AA battery is 1.5 volts), how do you make devices with a higher voltage requirement work without increasing the voltage of the battery?

Background - Key Facts

Given that the resistance (R) of a device – in this case the light bulb – is constant, if we were to change the current or voltage being provided to the device, we would have an effect on the power.

A light's intensity is proportional to the power (P) supplied to it

By increasing the voltage or current supplied to a circuit, we can increase the power, and therefore increase the intensity of the light.

How can we change current or voltage (I or V)?

We can test parallel and series circuits to see how they affect the intensity of the bulb, or we can test the number of batteries connected to a circuit and the effect of this on I, V, or power.

Batteries connected in a parallel circuit increase the available current (I) , but do not change the voltage (V) .

Batteries connected in a series circuit cause the voltage (V) to increase, resulting in a corresponding increase in current (I) .

With the Students

• Introduce the topic. Review definitions of keywords, as well as the topics mentioned in the Background section. Hand out the Ohm's Law Data Sheet and other materials.
• Group students . Depending upon the level of students, have them work on their own to develop experimental procedures that test the effect of the alignment of the batteries on voltage and current (and thus light intensity). Other students may follow the sample experimental procedure. Remind students that they are expected to answer the data sheet questions when the experiment is over with the information they gather.

• Comment on the effect of the number of batteries and their arrangement in the circuit on the power produced, and thus on the intensity of the light.

alternating current: Current that reverses direction at a regular rate.

ammeter: A device that measures current flowing through the circuit.

current: The flow of electrons. Current is read by opening the circuit and connecting the meter in series.

direct current: An electric current that flows in only one direction. The positive and negative terminals of a battery are always, respectively, positive and negative. The current always flows in the same direction between those two terminals.

light Intensity: The amount of light given off by a source such as a light bulb.

load: A device that consumes energy or power.

multimeter: A device that measures the current, voltage and resistance.

parallel circuit: A circuit that has two or more branches for separate currents from one voltage source.

potential: Electrical pressure, also called voltage.

power: The rate at which energy is delivered to something. (quantity / time): Measured in Watts.

resistance: The opposition of a body or substance to current passing through it, resulting in a change of electrical energy into heat, light, or another form of energy. Resistance is measured in Ohms. The resistance of a device is always the same (constant).

series: Circuit that only has one path for the electrons to flow.

voltage: The force that moves electrons. Voltage is read using the meter connected in parallel.

voltmeter: A device that measures the force with which electrons are flowing.

watt: The power expended when one ampere of direct current flows through a resistance of 1 Ohm.

Data Sheet & Questions: After students collect data on their data sheets, assign the questions as homework or a quiz/test. Review their answers to gauge their depth of comprehension.

• How is the brightness of the light bulb affected by the number of batteries connected in series? Explain.
• How is the brightness of the light bulb affected by the number of batteries connected in parallel? Explain.
• How is the current affected by the number of batteries connected in series? Explain.
• How is the current affected by the number of batteries connected in parallel? Explain.
• What are the advantages of connecting the batteries in parallel?
• What are the advantages of connecting the batteries in series?
• How might batteries be connected in a circuit to take advantage of both series and parallel characteristics?

Safety Issues

• Warn students that light bulbs get hot.
• Use the alligator clips and multimeters with care.

Take multimeter measurements quickly to avoid damage.

Conduct a demonstration that shows students just how much time it takes to use up the "juice" in a battery, and if it is better to use batteries in series or parallel. See the Ohm's Law 2 activity. This may be started before students begin to to work on the Ohm's Law 1 activity.

Students learn that charge movement through a circuit depends on the resistance and arrangement of the circuit components. In one associated hands-on activity, students build and investigate the characteristics of series circuits. In another activity, students design and build flashlights.

Students explore the basics of DC circuits, analyzing the light from light bulbs when connected in series and parallel circuits. Students measure and see the effect of power dissipation from the light bulbs.

Students are introduced to several key concepts of electronic circuits. They learn about some of the physics behind circuits, the key components in a circuit and their pervasiveness in our homes and everyday lives.

Students learn about current electricity and necessary conditions for the existence of an electric current. Students construct a simple electric circuit and a galvanic cell to help them understand voltage, current and resistance.

Brain, Marshall, Charles W. Bryant and Clint Pumphrey. How Batteries Work . Accessed November 6, 2011. http://electronics.howstuffworks.com/everyday-tech/battery.htm

Halliday, D., Resnick, R. and Walker, J. Fundamentals of Physics . USA: John Wiley & Sons, Inc., 2005.

Hambley, A. Electrical Engineering Principles and Application . USA: Prentice Hall, 2002.

Contributors

Supporting program, acknowledgements.

Creation of this activity was funded by Pratt & Whitney.

Last modified: April 19, 2021

Collection of Physics Experiments

Light bulb current-voltage characteristic, experiment number : 2097, goal of experiment.

The goal of this experiment is to show the dependency of voltage on current when measured on a light bulb (i.e. its current-voltage characteristic). This task is suitable as a problem task – students can present their hypotheses explaining the non-linearity of the current-voltage characteristic of a light bulb. Afterwards they can verify their hypotheses with the teacher's help.

This experiment is followed by a quantitative task that deals with the resistance of the light bulb filament.

According to Ohm’s law, there is a linear dependency between the current flowing through a wire and the voltage between the ends of the wire. The constant of proportionality is called conductance \(G=\frac{1}{R}\), where R is the wire resistance:

\[I=\frac{1}{R}\cdot U\tag{1}\]

In this experiment we measure how the voltage depends on the current, therefore we use Ohm’s law in the form of:

\[U=R\cdot I\tag{2}\]

The resistance of a wire depends on the dimensions of the wire the material it is made of (see the Dependence of Wire Resistance on Its Parameters experiment), and its temperature:

\[R=R_0(1+\alpha\Delta t),\tag{3}\]

where α is the resistance temperature coefficient and Δ t is the difference between initial and final temperatures. From the equation (3) we can see that the resistance of a wire increases with increasing temperature.

Electric power of the light bulb is given by the product of voltage and current:

\[P = U\cdot I\tag{4}\]

By substituting from Ohm's law we obtain:

\[P = \frac{U^2}{R}.\tag{5}\]

Provided that we know the voltage and the power, we can determine the resistance of the light bulb filament (at “factory conditions”):

\[R = \frac{U^2}{P}.\tag{6}\]

• 230 V light bulbs with a socket
• Controllable power supply with up to 10 V output (or a constant voltage source and an adjustable resistor of ca. 100 Ω
• Voltmeter and ammeter
• Connecting wires, crocodile clips
• Gas burner, matches

It is recommended to perform the experiment with digital voltmeter and ammeter connected to a computer; without the need to write down measured values, the measurement is much faster and students can use the saved time for inquiry-based discussion. However, it is also possible to use multimeters.

The first part of the experiment can be performed with an ordinary light bulb (e.g. 3.5 V/0.3 A), however, since it is necessary to remove the glass bulb to verify the hypotheses, it is recommended to use the 230 V light bulb from the beginning.

We connect the circuit according to the circuit diagram – we connect the bulb and ammeter in series to the voltage source, then we connect the voltmeter to the bulb in parallel.

We plot the dependence of voltage on current.

We discuss the non-linearity of the voltage-current characteristic with students. It is caused by the dependence of the bulb filament resistance on its temperature. Then, we remove the glass bulb and submerge the filament in water (more detailed description below) to ensure a constant temperature of the filament. We preform the experiment again.

As a conclusion, students should determine the bulb filament resistance from the I-V curve. Their results can be compared with the resistance determined from the information written on the light bulb. Once again, it is recommended to discuss the measured resistance.

Sample result

Our measurement was performed with a 240 V/60 W light bulb. Measured values are plotted in the graph below (Fig. 3).

From the graph we can observe that the dependence is non-linear, with increasing current the slope of the curve increases, and so does the wire resistance.

The measurement without the glass bulb with filament submerged in water is shown in a graph in Figure 4 – in this case, the current-voltage characteristic is linear and the wire resistance is approximately 97 Ω.

Removing the bulb

The procedure to removing the bulb, so that we are able to submerge the bulb filament in water and thus ensure its constant temperature, is shown in the video below. First, we heat the socket of the glass bulb for several seconds using a burner. Then we immerse the bulb in cold water. The thermal shock causes the bulb to crack and separate from the socket. It is recommended rotating the bulb during heating to ensure that it is heated evenly along the whole circumference.

Note: It is possible to hold the light bulb in bare hands during the heating. Glass is a bad heat conductor, so the rest of the bulb does not heat much.

For the second measurement, we submerge the remains of the light bulb (i.e. the bulb filament with the socket) into a jar filled with cold water. This will dissipate the heat generating by the filament.

Resistance at "factory" conditions

We performed the experiment with a 240 V/60 W light bulb. The wire resistance determined by the current-voltage characteristic is approx. 97 Ω.

The resistance can also be determined from the information given by the manufactures according to the relation (6):

\[R = \frac{230^2}{60}\ \Omega = 882\ \Omega \]

This discrepancy is another proof that wire resistance depends on its temperature – the working temperature of the bulb filament is higher than the temperature of the water we used to cool it.

Pedagogical notes

This experiment is suitable to be submitted as a problem task – the first measurement should be followed by a discussion of the fact that the I-V curve is non-linear, even though there is only a wire inside the bulb. Among the hypotheses, there should be one about the fact that a wire resistance also depends on something else, e.g. on temperature. Students should be able to find out that to obtain a linear I-V curve, we need to ensure a constant wire temperature. The teacher can then show them a way to conduct the experiment and repeat the measurement.

It is good to let the students determine the filament resistance from the I-V curve and from the power written on the bulb. The students can the discuss the obtained resistance. They can see that the resistance depends on the temperature of the conductor (and that a working temperature of a light bulb is much higher that the temperature at wich we performed the experiment).

If you want to use what is left of the light bulb, you can connect the bulb filament to the main power circuit (see video). The filament burns up very quickly, which demonstrates the necessity to cover the wire with a glass bulb filled with inert gas).

Technical notes

Be careful! Removing the glass bulb should be done by a teacher, so should be the second measurement with bare filament. There is a risk of burning and cutting yourself from the glass remains.

Given the fact that the experiment is performed using low voltage, it does not matter if a small amount of water remains in the bulb socket.

The bulb filament is very fragile; it can break when handled without care.

A glass jar has proven to be suitable as a water container. Some glass beakers can break after immersing the hot bulb filament.

General Atomics Sciences Education Foundation (GASEF)

Seeing the light: the physics and materials science of the incandescent light bulb.

This unit consists of an interlinked series of 6 multi-part experiments using inexpensive materials such as lights bulbs, heater wire, and an ohmmeter. In the first experiment, students discover that Ohm's law doesn't appear to be valid for the filament resistance of the light bulb. They then develop the understanding that this arises from the change in filament resistance with temperature. This experiment connects commonly used technology - the light bulb - with the mathematics of Ohm's law as well as with the dependence of the electrical properties of materials on their composition, length, and diameter. In a subsequent series of experiments, students investigate a 3-way bulb, a 3-way switch, and then a 3-way bulb in a 3-way switch socket. They develop the understanding - using observation, logical reasoning, and mathematical modeling - that a 3-way bulb consists of 2 filaments which are connected in parallel at the highest wattage setting. In the third experiment, students design a light bulb and describe the fabrication steps necessary to construct it; students are given some basic engineering information before attempting the experiment. They then dissect a light bulb and determine how close their earlier design resembles a real bulb. Finally, they must design and construct a light bulb that operates in air using materials that are similar to those found in a light bulb, but are oxidation resistant. These materials are available as a  kit from the General Atomics Sciences Education Foundation  as GASEF #013. GASEF #013 contains 10 20-cm long pieces of 0.003 inch diameter Kanthal AF wire, 2 20-cm long pieces of 0.010 inch diameter Kanthal AF wire, and 2 20-cm long pieces of 0.020 inch diameter copper wire.

This unit also consists of an extensive introduction with background information into advanced topics such as oxidation resistant materials, blackbody radiation, filament materials, filament environments, and a microscopic view of incandescence. Also explored are a brief history of the development of the light bulb and Edison's critical role in the methodology of experimental science, which set the subsequent standard for industrial research. A teacher's guide to all experiments, related mathematical problem sets, and solutions is included the module. This unit provides a natural tie to studies in economics and US history that involve the electrification of society, the industrial revolution, the rivalry between AC and DC distribution systems, and the growth of industrial laboratories. Students require a previous introduction to Ohm's Law and series and parallel circuits before beginning this unit. These experiments are aimed at grades 7-12, but would also be appropriate for an introductory university physics or materials science course.

This unit relates to the NSES physical science content standards in grades 5-8: "Energy is a property of many substances and is associated with heat, light, electricity ... Energy is transferred in many ways. Electrical circuits provide a means of transferring electrical energy when heat. light, sound, and chemical changes are produced;" and in grades 9-12: "Energy can be transferred ... in many ways. In some materials, such as metals, electrons flow easily, whereas in insulating material they can hardly flow at all."

Download Entire Unit (1.1MB PDF)

• TOP CATEGORIES
• AS and A Level
• University Degree
• International Baccalaureate
• Uncategorised
• 5 Star Essays
• Study Tools
• Study Guides
• Meet the Team

Testing ohms law on a light bulb and a resistor connected to a source of potential difference.

  Testing ohm’s law on a light bulb and a resistor connected to a source of potential difference.

Result of the experiment

• Light bulb.  

          Graph 1.1 voltage versus current graph for a light bulb.

Table 1.1 the current and resistance of a light bulb when         

  the voltage is varied.

B . Resistor

                      Graph 1.2 voltage versus current for a resistor

Table 1.2 the current and resistance of a resistor when         

This is a preview of the whole essay

The resistance shown in table 1.1 and table 1.2 (for both the light bulb and the resistor) was calculated using the following formula:-

                                   Resistance = voltage (V)        ……………………………. Equation 1

                                                           Current (A)                                                        

Discussion: - electric current  is the amount of charge that moves through the cross sectional area of a conductor per unit interval of time. Electric current occurs due to the movement of electric charges (electrons) through the conductor. In a certain conductor (wire, bulb, resistor) the electric resistance  is defined as the potential difference across its ends divided by the current flowing through it. According to ohm’s law  at a constant temperature the current through a conductor is proportional to the potential difference across it. Thus materials obeying ohm’s law will have a constant electric resistance at a constant temperature. ohm’s law also states that if the potential difference V between the ends of the conductor is altered and for every value of v, its corresponding value of current   I   flowing in the conductor is measured, a graph between V and I obtained is always a straight line. This means that current and voltage are directly proportional.

In this experiment two types of conductors were used. The first one was a light bulb. In Graph 1.1 it can be seen that the graph formed was not straight line but more of a curve. This in turn shows that the voltage and the current are not proportional. Also seeing from table 1.1 the light bulb does not have constant resistance. So the light bulb does not obey ohm’s law. This is because a light bulb is a non ohmic conductor.

In addition the resistance in light bulb is dependent on temperature (the bulb heats up as more voltage is added) and it increases significantly as the temperature (voltage) increases which is different from the resistor. So from this it can be said light bulb is a type of circuit which has a resistance which is dependent on temperature and therefore ohm’s law does not apply to a circuit which has a resistance that is dependent on temperature. Light bulb is therefore a non ohmic conductor.

The second conductor tested was a resistor. From the voltage versus current graph it formed it can see that it is a straight line. In addition the resistor fulfills another aspect of ohm’s law which states that the product of current flowing through a conductor and the resistor R is always equal to the potential difference V across the two ends of the conductor as long as the temperature and the other physical conditions of the conductor do not change.(V=R . I). By  checking the literature value of the resistor used the resistance was found to be 270 Ω. using this experiment the resistance was found within the range of 260 up to 267 Ω ±3. The slight difference can be due to systematic error.

Conclusion: -  The light bulb did not obey ohm’s law while the resistor obeys ohm’s law. In addition it can also be concluded that resistance can be dependent on temperature as seen in the resistance of the light bulb.

Limitations:-   the limitation of this experiment may be that the voltmeter and amphometer may have their own resistance which may affect the measuring of values. Since the experiment was only done once for each conductor systematic and random errors may affect the results obtained.

Improvement:   doing the experiment several times to get accurate readings.

Document Details

• Word Count 1004
• Page Count 5
• Level International Baccalaureate
• Subject Physics

Related Essays

To test the ohmic and non-ohmic behavior in a resistor and a bulb, physics lab report. aim: to find out how a light dependent resistor is affe..., design of a variable resistor, incandescent 100 watt light bulb ban: a bright idea .