Fundamentals of Circuits I: Current Models, Batteries & Bulbs

Name: 

Lab Partners: 

Date: 

Pre-Lab Assignment: 

Fundamentals of Circuits I: 

Current Models, Batteries & Bulbs 

(Due at the beginning of lab) 

1. Explain why in Activity 1.1 the plates will be charged in several different ways. 

2. Sketch below one arrangement of the battery, bulb and wire (other than the one in Fig. 3 

which you will try in Activity 1.2. 

3. At this time, which model for current in Fig. 6 do you favor Why 

PHYS-204: Physics II Laboratory 

i

Name: 

Date: 

Lab Partners: 

Fundamentals of Circuits I: 

Current Models, Batteries & Bulbs 

Objectives 

• To understand the nature of electric currents and why the current is the same at all points 

in simple circuits. 

• To understand that an electric potential difference (voltage) can cause a flow of electric 

charge in a conductor. 

• To gain practice in designing and building simple circuits with batteries, light bulbs and 

switches. 

• To learn to draw circuit diagrams using electrical symbols. 

• To learn to make measurements of current ant voltage using microcomputer-based probes 

Overview 

In the labs during the first part of this semester you are going to do a series of activities 

designed to help you develop a strong conceptual understanding of the nature of electric current 

and electric potential difference (commonly referred to as Voltage), and the essential features 

of simple electric circuits. These labs have been adapted from the Real Time Physics Active 

Learning Laboratories [1]. The goals, guiding principles and procedures of these labs closely 

parallel the implementations found in the work of those authors [1, 2, 3]. The ideas that you 

will learn in these labs are the same ones that go into making all the electrical devices that play 

an important role in our modern world-everything from electric lights and motors to TV sets, 

computers and photocopy machines. 

In several of these labs the electrical components we will work with are batteries and light 

bulbs. A battery is a device that uses chemical energy to do work on the electric charges that 

flow in it. As it does work it increases the electrical potential energy of these charges, which 

generates an electric potential difference. 

The energy added to the electric charge by the battery can be used to operate an electrical 

device. In today’s experiment that device will be a light bulb. But in order to deliver the 

energy to the light bulb the electric charge must flow through the battery and light bulb. This 

requires the light bulb and battery to be connected using conductors, materials that allow 

electric charges to flow in them. 

In this lab you will consider several models that might explain the flow of charge and 

predict the measurements that would result if the model is correct. You will then make the 

measurements to determine which of the models correctly describes the flow of charge, and 

which models do not. 

PHYS-204: Physics II Laboratory 1

Fundamentals of Circuits I: Current Models, Batteries & Bulbs v 0.1 

Investigation 1: 

Models describing electric current 

What is electric current Today, as you can read in any textbook, we believe that current is 

produced by electric charges in motion. The electric current in a copper wire, for example is 

produced by the motion of electrons through the wire. Do we know this If so, how do we 

know How can we experimentally distinguish this model of current from other models 

These questions were studied and tested by Michael Faraday, a famous early nineteenth 

century scientist. Faraday examined the effects of electricity from many different sources, 

including animals such as electric eels, batteries, and electromagnetic induction in addition to 

the electric charge produced by rubbing objects, and concluded that ”electricity, whatever may 

be its source, is identical in its nature.” 

Let’s put Michael Faraday’s conclusion to a small test. Is the electricity in “static electricity” 

identical in nature to the electricity in a battery or power supply Objects which are rubbed in 

particular ways are found to attract or repel other objects which have been rubbed in particular 

ways. These forces between objects are attributed to a property of matter known as charge. 

Rubbing the objects produces and induced charge on the objects. This induced charge is an 

example of static electricity. 

The purpose of the first activity is to compare the current produced the static charges 

deposited by rubbing materials together. to the current produced by a battery or power supply. 

You will observe a demonstration using the following materials: 

• Large variable capacitor with two metal plates 

• Electroscope 

• foil covered Styrofoam ball on a string 

• 300 V battery pack or power supply 

• PVC rod and wool cloth 

• acrylic rod and polyester or silk cloth 

• alligator clip leads 

Activity 1.1: Comparing charge from a power supply and charge produced 

by rubbing 

Step 1: The metal plates of a variable capacitor and the conducting ball will be set up as 

shown in Fig. 1. 

By charging the metal plates in two ways, we can test whether or not the different charging 

methods have different effects on the ball dangling between the plates. The two methods 

we will test are: 

a. Electrostatic Charging by Rubbing. Stroke one plate with a PVC (gray) rod that has 

been rubbed with the cat fur or wool. Repeat this several times. Stroke the other 

plate with the acrylic (clear) rod that has been rubbed with the silk or polyester 

cloth. 



+ 

+ 

+ 

+ 

+ 

− 

− 

− 

− 

− 

Figure 1: Visualizing Current 

b. Charging with a Battery or power supply. Connect a wire from the negative terminal 

of the battery pack to one of the angle irons. At the same time connect a wire from 

the positive terminal of the battery pack to the other plate. 

Step 2: With the metal-covered ball removed from between the plates, charge the plates using 

the charged rubber and glass rods (method a). Measure the effects with an electroscope. 

Step 3: Adjust the metal plates so that the gap between them is just barely larger that the 

diameter of the metal covered ball. Again charge the plates using the charged rubber and 

glass rods. Then carefully lower the ball between the plates. You should see something 

pretty unusual. 

Question 1.1 What happened when the ball was placed between the plates In terms 

of the attraction and repulsion of different types of charges, explain why this unusual 

phenomenon happened. 

Step 4: With the ball removed from between the plates, charge the plates by connecting the 

power supply (method b). 

Step 5: Then carefully lower the ball between the plates, and again observe its behavior. 

Question 1.2 Describe what happened when the power supply was used to ”charge” the 

plates. What differences (if any) between method (a) and method (b) did you observe in 

the response of the ball to the charges on the plates 



Question 1.3 Do the charges generated by rubbing and by the power supply cause different 

effects If so, describe them. Do the charges generated in these two ways appear to 

be different 

The rate of flow of electric charge is more commonly called electric current. If charge ∆Q 

flows through a conductor in time ∆t, then the current can be expressed mathematically 

by the relationship 

I = ∆Q 

∆t . 

The SI unit of current is called the ampere (A). One ampere represents the flow of one 

coulomb of charge through a conductor in a time interval of one second. Another common 

unit of current is the milli-ampere (mA). (1 ampere = 1000 milli-amperes). It is common 

to refer to current as ”amps” or ”milliamps.” 

(a) 

+ 

− 

(b) 

+ 

− 

+ 

− 

+ 

− 

+ 

+ 

+ 

+ + 

+ + 

+ + 

+ 

v 

− 

− 

+ 

+ 

− 

− 

− 

− − 

− 

− 

− 

v 

− 

− 

+ 

− 

+ 

− 

Figure 2: Moving Charges 

Question 1.4 Consider Figs. 2(a) and 2(b). Do both figures show a current to the right 

Explain. 

Activity 1.2: Arrangements that Cause a Bulb to Light 

In this activity, you can begin to explore electric current by lighting a bulb with a battery. You 

will need the following: 

• flashlight bulb (#14) 

• flashlight battery (1.5 V D cell) 



• one wire (6 inches or more in length) 

Step 1: Use the materials listed above to find some arrangements in which the bulb lights and 

some in which it does not light. For instance, try the arrangement shown below. 

Figure 3: A wiring configuration that might make a bulb light with a battery. 

Question 1.5 Sketch below two different arrangements in which the bulb lights. (Note: 

there are a total of four including the one pictured above). 

Question 1.6 Sketch below two arrangements in which the bulb doesn’t light. 

Question 1.7 Describe as fully as possible what conditions are needed if the bulb is to 

light, and why the bulb fails to light in the arrangements drawn in answer to Question 1.6. 

Activity 1.3: Other Materials Between the Battery and Bulb 

In the previous activity you found that a wire, properly connected to a battery and a 

bulb, allows current to flow. By definition we refer to materials that allow current flow 

as conductors. By contrast materials which do not allow current flow are called nonconductors. 



Lets examine some common materials to see which are conductors and which are nonconductors. 

We can do that by determining which materials allow the bulb to light. You 

will need 

• common objects: paper clips, pencils, coins, rubber bands, fingers, paper, keys etc. 

Connect a single wire, the battery, and a bulb so that the bulb lights. Choose one of the 

arrangements drawn in your answer to Question 1.5. Then, with the help of your partner, 

stick in a variety of the common objects available between the battery and the bulb. 

Question 1.8 List the materials that allow the bulb to light. 

Question 1.9 List the materials that prevent the bulb from lighting. 

Question 1.10 What types of materials seem to be conductors What types seem to be 

non-conductors 

By now you will have discovered that it is difficult to hold your circuits together From 

here on, you can make it easier by using a battery holder and a bulb socket. These things, with 

the addition of a switch are found on the circuit board provided. 

Activity 1.4: Using a Battery Holder, Bulb Socket and Switch 

For this activity, in addition to the materials you’ve already used, you will need: 

• battery holder (for a D cell) 

• several wires (6 inches or more in length) 

• flashlight bulb socket 

• contact switch 

Step 1: Examine the bulb socket carefully. Examine what happens when you unscrew the 

bulb. Note which parts of the bulb make contact with which parts of the socket. 

Step 2: Examine the bulb closely. 



Figure 4: Diagram of wiring inside a light bulb: The dashed lines show wires hidden from view. 

The black portion is a ceramic insulator, while the grey pieces are a conductors. 

Question 1.11 Why is the filament of the bulb connected in this way 

Question 1.12 Explain which parts of the bulb socket come in contact with which parts 

of the bulb. Why doesn’t the bulb light when it is unscrewed 

Prediction 1.1 Consider the circuit shown in Fig. 5. If the switch is open, will the bulb 

light Will the bulb light when the switch closed Explain your predictions. 

Figure 5: A circuit with a battery, light bulb and switch. 

Step 3: Wire the circuit shown in Fig. 5 and test it. Use the battery holder, bulb socket, and 

switch on the circuit board provided. 

Step 4: Close the switch and leave it closed so that the bulb remains lit for 20 seconds. Release 

the switch and immediately feel the bulb. 



Question 1.13 What did you feel 

when there is a current through it 

Besides giving off light, what happens to the bulb 

Question 1.14 What can you say about the path needed by the current to make the bulb 

glow Your explanation should be based on the observations you have made so far. 

Model A 

Next we explore and contrast some competing models for current in a circuit. Consider 

a circuit equivalent to the one shown in Fig. 5 with the switch closed. Fig. 6 depicts 

four different models for current in this circuit. These models are based on models that 

students often propose. These models are described below. 

1 

Model B 

1 

2 

2 

Model C 

1 

Model D 

1 

2 

2 

Figure 6: Four possible models for current. 

Model A: Current flows from the positive terminal of the battery through wire #1 and into the 

bulb. The bulb uses up all of the current and no current flows back to the battery 

in wire #2. 

Model B: Currents flow from both terminals of the into the bulb. 

Model C: The current flows from the positive terminal of the battery into the bulb. The bulb 

uses up some of the current and a smaller current returns to the negative terminal 

of the battery. 

Model D: A Current flows from the positive terminal of the battery into the bulb, and the 

exact same current returns to the negative terminal of the battery. 



Question 1.15 How can you determine which model, if any, correctly describes the current 

through the bulb What would you measure, and where would you measure it Discuss 

what measurements you might make to eliminate at least three of the four competing 

models for current. Talk things over with your partners, and explain your reasoning. 

In Activity 1.5 you will use the computer based laboratory system and two current probes 

in your circuit to measure current and test the four models above. In addition to the 

battery, bulb and wires you used above, you will need: 

• Computer with Logger-Pro software 

• Lab Pro interface 

• two current probes 

The current probe is a device that measures current. Your computer will take measurements 

from the current probe and display them, as a function of time, on the computer 

screen. The current proble will allow us to measure the current at different locations and 

under different conditions in electric circuits. 

− + 

CP 

Figure 7: Measuring current in a circuit with a battery, bulb and current probe. 

In order to measure a current, the current must pass through the current probe. For 

example, to measure the current in the bottom wire of the circuit in Fig. 5, the current 

probe should be connected as shown in Fig. 7. To connect the current probe at this 

location we must disconnect the circuit at the point where you want to measure the 

current (the bottom wire), and insert the current probe. That is, disconnect the circuit, 

put in the current probe, and reconnect with the probe in place. 

Keep in mind that the current probe measures both the magnitude and direction of the 

current. Just like we did for velocities, forces, and other vector quantities in Physics I, 

we distinguish opposite directions for current flow by positive and negative. A current 

in through the + terminal and out through the - terminal (in the direction of the arrow) 

will be displayed as a positive current. By contrast, when the current probe measures a 

negative current, the current is directed into the − terminal and out of the + terminal of 

the probe. 

Take a close look at Fig. 8. If the current in the loop is clockwise both ammeters will 

measure currents which are positive. 



+ − 

CP1 

− + 

CP2 

Figure 8: Circuit with two current probes, one measuring current from the positive terminal of 

the battery, the other measuring current into the negative terminal of the battery. Note how 

the + and − terminals of the current probes are connected, 

Prediction 1.2 The table below is a prediction table for each of the four models. Before 

making any measurements fill in Table 1 to show how the readings of current probe 1 and 

current probe 2 in the circuit in Fig. 8 would compare with each other for each of the 

current models described in Fig. 6. 

Model A 

Model B 

Model C 

Model D 

Probe 

CP1 

CP2 

CP1 

CP2 

CP1 

CP2 

CP1 

CP2 

Current 

+, − or 0 

CP1>CP2, CP1


Current 2 (A) 

Current 1(A) 

Time (s) 

Step 3: Zero the probes with the switch open. 

Step 4: Set up the circuit in Fig. 8 with the terminals marked + and − as shown. Begin 

graphing, and try closing the switch for a couple of seconds and then opening it for a 

couple of seconds. Repeat this several times while you are graphing. Sketch your graphs 

on the axes above. 

Note: You should observe carefully whether the current through both probes is essentially 

the same, or if there is a significant difference (more than a few per cent), and whether it 

is positive or negative. 

Question 1.16 How could you determine if an observed difference in the currents read by the 

top and bottom current probes is real or if it is the result of small calibration differences in the 

current probes 

Question 1.17 Did you observe a significant difference in the currents at these two locations 

in the circuit, or was the current the same 

Question 1.18 Based on your observations, which models seems to correctly describe the behavior 

of the current in your circuit. Explain carefully based on your observations. 




Using electric circuit symbols 

Representing electric circuits by drawings, like Fig. 5, can be very tedious. It can also be 

confusing for circuits that have many components. To make it easier to design electric circuits 

standard symbols have been established to represent the various components that make up an 

electric circuit. A few of these are shown below. More will be introduced in future experiments. 

V = 1.5V 

S 

+ − 

Battery 

Switch 

R 

I 

Bulb 

Figure 9: Circuit Elements 

Wire 

Activity 2.1: Drawing circuits 

Question 2.1 Draw the circuit represented by Fig. 5 using the symbols above. 

Question 2.2 On the battery symbol, which line represents the positive terminal-the long one 

or the short one (Note: you should try to remember this convention. There are many situations 

in which it is important to distinguish the positive and negative terminals.) 




Current and Electric Potential Difference 

Since a battery is a device that has an electric potential difference across its terminals, it 

is capable of giving energy to charges, which can then flow as a current through a circuit. 

Exploring the relationship between the potential differences in a circuit and the currents that 

flow in that circuit is an essential part of developing an understanding of electrical circuits. 

Since potential differences are measured in volts, a potential difference is informally referred 

to as a voltage, and usually denoted by the symbol V . Voltage is an informal term for potential 

difference. If you want to talk to physicists, you should refer to potential difference. Communicating 

with a sales person at the local Radio Shack store or buying batteries at a hardware 

store is another story. There you should probably refer to voltage. We will use these two terms 

interchangeably. 

You will use voltage probes to measure electric potential difference. The voltage probe has 

two clips. When the clips at the ends of the wires are connected at two points in a circuit the 

computer can measure the potential difference. Fig. 10 shows our simple circuit from Fig. 5 

with a voltage probe connected to measure the voltage across the battery. Note that the word 

across describes how the voltage probes are connected. 

+ 

VP1 

− 

Figure 10: Voltage probe connected to measure potential difference of the battery 

Let’s measure the potential difference across different elements of this circuit. You have 

available the following equipment. 

• Computer with Logger-Pro software 

• Lab Pro interface 

• D-cell battery and holder 

• light bulb and socket 

• SPST switch 

• two voltage probes 



Activity 3.1: Electric Potential (Voltage) 

Step 1: Unplug the current probes from the interface, and connect the voltage probes to 

channels 1 and 2. 

Step 2: Open the experiment file L1A3-1(Two Voltages) to display the axes that will allow 

you to compare two voltages. 

Step 3: Connect the circuit shown in Fig. 9, but do not connect the voltage probes yet. 

Step 4: Zero the voltage probes, being sure that the clips of the voltage probes are not connected 

to anything. 

Step 5: Connect both clips to the negative end of the battery holder in the circuit. Click on 

the collect button to start graphing. Collect data with the switch open, and with the 

switch closed. Record the potential difference with the switch open, and with the switch 

closed. 

V open = volts V closed = volts 

Step 6: Move the red clip and connect it at the other end of the wire connecting the negative 

terminal of the battery to the light bulb. Connected this way the voltage probe will 

measure the potential difference between the ends of the wire. 

Step 7: Collect data to determine the potential difference with the switch open, and with the 

switch closed. 

V open = volts V closed = volts 

Question 3.1 What do you conclude about the potential difference when the two leads 

from the voltage probe are connected to the same point What do you conclude about the 

potential difference between the two ends of the same wire 

Prediction 3.1 In the circuit in Fig. 11, how would you expect the voltage difference 

across the battery to compare to the voltage across the bulb with the switch open and with 

the switch closed Explain. 

Step 8: Now test your prediction. Connect voltage probe 1 across the battery, and voltage 

probe 2 across the light bulb, as in Fig. 11. 

Step 9: Collect data and make graphs of the two potential differences. Make sure the switch 

is closed during part of the time that the computer is collecting data, and open during 

part of the time. 



+ 

+ 

VP1 

− 

− 

VP2 

Figure 11: Circuit with two voltage probes 

Step 10: Sketch the graphs on the axes below. On the graph show the time intervals during 

which the switch was closed and when the switch was open. 

Voltage 1 (V) 

Voltage 2 (V) 

2 

0 

-2 

2 

0 

-2 

Time (s) 

Question 3.2 What do you conclude about the voltage across the battery and the voltage across 

the bulb when the switch is open and when it is closed Are the graphs the same Why or why 

not Is this in agreement with your prediction 3.1 What is the effect of closing the switch 

Activity 3.2: Electric potential difference and current 

Now we want to find out about the potential difference across the battery, and the current that 

flows around the circuit. 

Step 1: Unplug the voltage probe from channel 2, and plug a current sensor into channel 2. 



+ 

VP1 

− 

− + 

CP 

Figure 12: Measuring both current and potential difference. 

Step 2: Connect a circuit with the battery, switch and light bulb. Include the current sensor 

and voltage probe in the circuit connected as in Fig. 12. 

Step 3: Open experiment file L1A3-2 (Current and Voltage) to display the axes that follow. 

Voltage 1 (V) 

2.0 

0 

-2.0 

Current 2 (A) 

Time (s) 

Step 4: Collect data to make graphs of the potential difference across the battery and the 

current through the circuit while you open and close the switch several times. Use the 

”Store Latest Run” command in the Data menu to keep your results. Sketch the graphs. 

Be as accurate as you can to show the magnitudes of the potential difference and the 

current. 

Potential difference V Current amps. 

Question 3.3 What happens to the current through the circuit as the switch is closed 

and opened What happens to the potential difference across the battery 



Prediction 3.2 Now suppose you connect a second bulb in the circuit, as in Fig. 12. 

How do you think the potential difference across the battery will compare to the potential 

difference with only one light bulb Will it change significantly 

+ 

VP1 

− 

− + 

CP 

Figure 13: Circuit with two light bulbs 

Step 5: Connect the circuit as in Fig. 13. 

Step 6: Again collect data to make graphs of Potential difference and current. Sketch your 

graphs, using dotted lines to show your results with two bulbs. Represent the magnitudes 

of the current and potential as accurately as you can. 

Question 3.4 Was the current through the circuit significantly different with two bulbs than it 

was with one bulb (more than a few per cent) 

Question 3.5 Was the potential difference significantly different with two bulbs than it was 

with one bulb (more than a few per cent) 

Question 3.6 Does the battery appear to be a source of constant current, constant potential 

difference, or neither when additional elements are placed in the circuit 



These laboratory exercise has been adapted from the references below. 

References 

[1] David R. Sokoloff, Priscilla W. Laws, Ronald K. Thornton, and et.al. Real Time Physics, 

Active Learning Laboratories, Module 3: Electric Circuits. John Wiley & Sons, Inc., New 

York, NY, 1st edition, 2004. 

[2] Priscilla W. Laws. Workshop Physics Activity Guide, Module 4: Electricity and Magnetism. 

John Wiley & Sons, Inc., New York, NY, 1st edition, 2004. 

[3] Lilian C. McDermott, et.al. Physics by Inquiry, Volumes I & II. John Wiley & Sons, Inc., 

New York, NY, 1st edition, 1996.

Fundamentals of Circuits I: Current Models, Batteries & Bulbs

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