physics lab

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Augusta Technical College

PHYS 1110L - Online Lab 5: Electromagnetic Induction

Objectives:

The purpose of this experiment is to investigate Faraday’s law of induction and how an electrical

potential (voltage) is generated in a coil of wire by a changing magnetic flux. We will also

investigate how an electrical current-carrying coil of wire creates a magnetic field, that when

changing, can induce an electrical potential and current in a neighboring coil.

Equipment:

• Computer

• PhET Faraday's Electromagnetic Lab Simulation Software

Theory:

• The principle of electromagnetic induction is one of the most technologically important and is

the basis for much of our modern civilization through its application in generating and

transmitting electrical energy. All electrical energy resulting from hydroelectric (water), coal,

oil, gas, and nuclear-fueled Power Plants use electromagnetic induction, as well as does wind

power. (Only solar electrical energy generation is different and uses the “photoelectric effect”

to convert rays of sunlight directly into electrical energy.)

• Electromagnetic induction creates an electrical potential in a coil of electrically conductive

wire when the magnetic flux passing through the wire coil changes with time.

• The magnetic flux  is the number of magnetic field lines passing through the wire coil and is

defined mathematically as the total magnetic field B through a loop of wire with cross sectional

area A multiplied by the angle  between the normal to the plane of the loop and the magnetic

field direction (Equation 1):

 = 𝑩 →

⋅ 𝑨 →

= 𝑩𝑨 𝒄𝒐𝒔 𝜽 (1)

Where the unit of magnetic flux is the Weber (Wb), which is equal to T.m2 or V.s.

• According to Faraday’s Law of Induction, a changing magnetic flux through the coil induces

a voltage or an electromotive force (emf) in the coil (Equation 2):

𝜺 = −𝑵 𝜟𝑩

𝜟𝒕 (2)

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Where:  is the induced voltage or emf

N is the number of turns of wire in the coil

 B is the magnetic flux through the coil

t is time in units of seconds

• In this experiment, we will use these equations for magnetic flux (Equation 1) and Faraday’s

Law of Induction (Equation 2) as “design” equations. We will explore the effect on the induced

voltage as a function of changing the key variables of: magnetic field strength B, coil area A,

number of loops of wire in the coil (N), and the rate that the magnetic flux is changed in the

coil with time.

• Note also by Ohm’s Law, an induced voltage or emf across a resistor will lead to an induced

current (Equation 3):

RI indind / = (3)

• The induced electrical current moving in a loop of wire generates its own induced magnetic

field. The induced current flows in a direction such that the induced magnetic field has a

direction to oppose the original flux change. This is known as Lenz’s Law and mathematically

it is captured by the negative sign in Faraday’s Law (Equation 2) and is illustrated in Figures

1 and 2 below.

Figure 1: The permanent magnet illustrated on the left side of the figure is moving towards the

coil of electrically conductive wire and so the magnetic flux is increasing. By Faraday’s Law of

Induction, the increase in magnetic flux in the wire coil results in an induced voltage and current

in the coil. The induced current in the wire coil (shown by the right illustration in the figure)

moves counter-clockwise so that the induced magnetic field (pointing left) opposes the increase in

magnetic flux from the approaching permanent magnet. Note the Second Right Hand Rule (far

right illustration) is used to determine the induced current direction.

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Figure 2: In this case, the permanent magnet illustrated on the left side of the figure is moving

away from the coil of wire and so the magnetic flux is decreasing. By Faraday’s Law of Induction,

the decrease in magnetic flux in the wire coil also results in an induced voltage and current in the

coil. However, the induced current in the wire coil (shown by the right illustration in the figure)

now moves counter-clockwise so that the induced magnetic field (pointing right) opposes the

decrease in magnetic flux from the retreating permanent magnet. Note again the Second Right

Hand Rule (far right illustration) is used to determine the induced current direction.

• Electromagnetic induction can also occur by replacing the permanent magnet in Figures 1 and

2 with a current carrying coil of wire that generates its own magnetic field (Figure 3). The

current carrying coil (called the “Primary” coil) acts as an electromagnet. The magnetic field

of the primary coil can be made to project through an adjacent coil of wire (called the

“Secondary” coil). A voltage will be induced in the secondary coil if the magnetic flux from

the primary coil changes with time. In this way electrical energy from the primary coil is

transferred across free-space to the secondary coil. This phenomenon is called Mutual

inductance and is the basis for the transformers that increase and decrease electrical voltage

(e.g., the transformer that allows you to charge your cell-phone with 5 volts from a 120V wall

plug!) and non-contact electrical charging used more and more in cell-phones, electric tooth

brushes, and soon electric cars.

Figure 3: The magnetic field produced by the current carrying coil (Coil 1, Primary coil)

projects through the adjacent coil (Coil 2, Secondary coil). A voltage is induced in the Coil 2

when the magnetic flux from Coil 1 changes.

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Part A – Magnetic Field Lines and Field Strength:

• In this part of the experiment we will map the magnetic field around a permanent bar magnet

and measure the strength of the magnetic field (B) at two different distances from the bar

magnet, and at two different strengths of the bar magnet.

• Open PhET Faraday's Electromagnetic Lab Simulation Software. Flash Player is required to

run this simulation:

➢ https://phet.colorado.edu/en/simulation/faraday

➢ Open the first tab at the upper left of the screen, “Bar Magnet”

➢ Activate (check box) the options “Show Field”, “Show Compass”, and “Show Field Meter”

(Figure 4).

Figure 4: PhET electromagnetic induction “Bar Magnet” simulation (left illustration) showing

the bar magnet, magnetic field lines, compass, and magnetic field meter. The right illustration

shows the options activated by checking the boxes.

• Move the blue Magnetic Field Meter to a corner of the screen. It will be used later.

• The permanent bar magnet can be positioned in the center of the screen. The bar magnet has

a red-colored segment and a “N” on the right side signifying the “North Pole” and a white-

colored segment with a “S” on the left end signifying the “South Pole”.

• Note that the compass is also a tiny permanent magnet with a red North Pole and white South

Pole. The compass needle will align tangent to the magnetic field lines.

• Starting with the compass just to the right of the North Pole, slowly drag the compass from the

north to the South Pole and sketch the magnetic field lines and the orientation of the compass

needle and the north and South Pole of the compass needle (See the sample magnetic field line

in Figure 4). Use the sketch box in Part A of the Experimental Data section of this Lab Handout

to sketch the magnetic field lines.

Bar Magnet

Magnetic Field Meter

Compass

Sample Magnetic Field Line

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• Next, move the compass to a corner of the screen. Then drag the magnetic field meter about

one centimeter distant from the North Pole along the axis of the bar magnet, just to the right of

the magnet (see Figure 5). Adjust the bar magnet strength to 50% and record the value of the

magnetic field (B) read from the meter in the Part A Data Table. Then, without moving the

magnetic field meter, increase the bar magnet strength to 100% and again record the value of

the magnetic field (B) read from the meter in the Part A Data Table.

Figure 5: PhET electromagnetic induction “Bar Magnet” simulation showing the position of

the magnetic field meter 1 centimeter from the right end of the bar magnet.

• Repeat this experiment after moving the position of the magnetic field meter an additional

centimeter (total 2 cm) from the North Pole in line with the axis of the bar magnet.

• Compare the values of the magnetic field (B) at the position of 1 cm and 2 cm for the 100%

bar magnet strength. Think hard about this difference!

• Save a screenshot (screen capture) of the simulation magnetic field for one of your trials and

include in the graph section of your lab report.

Part B – Induced Voltage/Current:

• In this part of the activity, we will investigate the magnitude and direction of the induced

current in a coil due to changes in the magnetic flux.

• Open PhET Faraday's Electromagnetic Lab Simulation Software:

➢ https://phet.colorado.edu/en/simulation/faraday

➢ Open the second tab at the upper left of the screen, “Pickup Coil”.

➢ Activate the options “Show Field”, “One Loop”, and “Show Electrons” (Figure 6). Use

the default settings for Loop Area (50%) and change the Magnet Strength to 50%.

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Figure 6: PhET electromagnetic induction “Pickup Coil” (Left illustration), showing the

permanent bar magnet, coil of wire and light bulb, and magnetic field, and the settings tables

(Right illustration).

• Change the variable settings as described below and then move the North Pole of the bar

magnet through the coil slowly and then quickly and observe the relative “brightness” of the

light-bulb between the “fast” and “slow” magnet movement and between the changes in the

variables. The “brightness” increases as the length of the “light rays” emanating from the light-

bulb increase. Record your observations in the Part B Data Table. Return the values to the

starting settings after each change in variables:

o Increase the Coil (Loop) Area from 50% to 100%.

o Increase the Magnetic Field Strength from 50% to 100%.

o Increase the Number of Coils from 1 to 3.

• Record also what happens if you place the North Pole of the Bar Magnet inside the coil and do

not move it.

• Think what combination of “design” variables would produce the greatest induced voltage!

• Continue the experiment by setting the coil area and magnetic field strength to 100%, the

number of coils to 3, and replace the lightbulb with the “Volt Meter” (Figure 7). In this case,

move the bar magnet’s North Pole slowly towards the coil and observe how the needle on the

voltmeter moves (left or right). Observe if there is a difference in the needle direction when

you move the bar magnet North Pole towards or away from the coil. Repeat this experiment

using the bar magnet’s South Pole.

• Refer to the equations for Magnetic Flux (Equation 1) and Faraday’s Law of Induction

(Equation 2) to understand how the Coil Area and Magnetic Field Strength (Equation 1) and

Number of Coils (Equation 2) would affect the induced voltage.

• Save a screenshot (screen capture) of the simulation induced voltage/current for one of your

trials and include in the graph section of your lab report.

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Figure 7: PhET electromagnetic induction “Pickup Coil” showing the permanent bar magnet,

coil of wire and Volt Meter.

Part C – Mutual Induction:

• In this part of the experiment we will investigate how the principle of mutual induction allows

an electrically powered “Primary” wire coil to transfer electrical energy to a “Secondary” wire

coil across free space. A current carrying coil produces a magnetic field and can replace the

permanent magnet in Part B.

• Open PhET Faraday's Electromagnetic Lab Simulation Software:

➢ https://phet.colorado.edu/en/simulation/faraday

➢ Open the fourth tab at the upper left of the screen, “Transformer”

➢ Activate (check box) the options “Show Field”, “Show Electrons”. Set the Primary coil to

“4 Loops” and the Secondary Coil to 3 Loops (Figure 8).

Figure 8: PhET electromagnetic induction “Primary Coil” powered by a DC Battery (Left

illustration), the Secondary Coil with a light bulb, and the settings tables (Right illustration).

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• Noting that the DC (Direct Current) battery provides a constant source of electrical power to

the Primary Coil, and referencing Equations 1 and 2, observe and record the change (if any) of

the magnetic field produced by the Primary Coil and the relative “brightness” of the light-bulb

attached to the Secondary Coil when the Primary Coil is stationary. Record your observations

in the Part C Data Table.

• Observe and record the change (if any) of the magnetic field produced by the Primary Coil and

the relative “brightness” of the light-bulb attached to the Secondary Coil when the Primary

Coil is moved slowly and then quickly through the Secondary Coil. Record your observations

in the Part C Data Table.

• Now change the setting of the Primary Coil from DC to AC (Alternating Current set at 100%)

and activate the “Volt Meter” instead of the light bulb (Figure 9).

Figure 9: PhET electromagnetic induction “Primary Coil” powered by an AC power source

(Left illustration), the Secondary Coil with a Volt Meter, and the settings tables (Right

illustration).

• Position the Primary coil as shown in Figure 9. Noting that the AC (Alternating Current)

provides a continuously varying supply of electrical power to the Primary Coil, and referencing

Equations 1 and 2, observe and record the change (if any) of the magnetic field produced by

the Primary Coil and the movement of the Voltmeter Needle attached to the Secondary Coil

when the Primary Coil is stationary. Record your observations in the Part C Data Table.

• Now move the Primary Coil into the center of the Secondary Coil. Observe and record the

change (if any) of the magnetic field produced by the Primary Coil and the movement of the

Voltmeter Needle attached to the Secondary Coil when the Primary Coil is stationary. Record

your observations in the Part C Data Table.

• Save a screenshot (screen capture) of the simulation mutual inductance for one of your trials

and include in the graph section of your lab report.

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Part D – Electrical Power Generation:

• In this part of the experiment we will investigate how the principle of mutual induction allows

electrical power to be generated by rotating a magnet near a coil of electrically conducting

wire. This is of great technological importance as this is the way that hydroelectric, coal, oil,

gas, nuclear, wind, and tidal Power Plants generate electricity for our modern civilization.

• Open PhET Faraday's Electromagnetic Lab Simulation Software:

➢ https://phet.colorado.edu/en/simulation/faraday

➢ Open the fifth tab at the upper left of the screen, “Generator”

➢ Activate (check box) the options “Show Field”, “Show Compass”. Set the Primary coil to

“2 Loops”, the Bar Magnet strength to 50% and the “Loop Area” to 50% (Figure 10).

Figure 10: PhET electromagnetic induction “Generator” powered by an external power source

(“Hydroelectric Power” using water behind a dam) that turns a water-wheel with a magnet

attached (a “Turbine”), which causes a continuously changing magnetic field inside the

adjacent wire coil.

• Vary the following “design” variables and record your observations of the maximum voltage

produced and the movement direction of the voltmeter needle in the Part D Data Table. Return

the values to the starting settings after each change in variables:

o Bar Magnet Strength from 50% to 100%

o Coil (Loop) Area from 50% to 100%

o Increase the external power supply water-flow-rate to increase the “Turbine”

revolutions per minute (RPM) from 10RPM to 50RPM. Watch the change in the

magnetic field carefully at the lower 10RPM setting.

• Think what settings of the variables will produce the greatest electrical power output!

• Save a screenshot (screen capture) of the simulation power generation for one of your trials

and include in the graph section of your lab report.

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Analysis:

• Part A – Magnetic Field Lines and Field Strength:

1. Magnetic Field Lines: As you sketch the magnetic field lines, include which part of the

compass needle points towards the North Pole of the bar magnet. The North or South Pole

of the Compass needle? Include this in your Lab Report.

2. Magnetic Field Strength: How much does the value of the magnetic field (B) increase on

the magnetic field meter when the magnetic field strength of the bar magnet was doubled

at 1 cm from the North Pole of the magnet? Does this make sense? Why? Explain in your

Lab Report.

3. Magnetic Field Strength: Did the value of the magnetic field (B) increase or decrease when

the magnetic field meter was moved from 1 cm to 2 cm (double the distance) at 100% bar

magnet strength? Did the value of the magnetic field (B) double, fall to half, or something

else? (Hint – Think of how the electrostatic Coulomb Force changes with distance!)

Explain in your Lab Report.

• Part B – Induced Voltage/Current (Reference Equations 1 and 2 in your responses!):

1. How does the speed at which the bar magnet is moved effect the “brightness” of the light

bulb? Explain in your lab report.

2. How does the coil area effect the “brightness” of the light bulb? Explain in your lab report.

3. Why does magnetic field strength effect the “brightness” of the light bulb? Explain in your

lab report.

4. Why does the number of coils effect the “brightness” of the light bulb? Explain in your

lab report.

5. What happens to the lightbulb “brightness” when the bar magnet is placed inside the coil

of wire and not moved? Explain in your lab report.

6. What happens to the lightbulb “brightness” if you move the coil over the bar magnet instead

of the bar magnet through the coil? Explain in your lab report.

7. What direction does the voltmeter needle move when the North Pole is pushed into or

withdrawn from the wire coil? The South Pole? Explain in your lab report.

8. What settings of the electromagnetic induction “design” variables (Equations 1 and 2) give

the greatest voltage? Explain in your lab report.

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• Part C – Mutual Induction:

1. How does the “brightness” of the light-bulb change when the DC powered Primary coil is

stationary? Explain in your lab report.

2. How does the “brightness” of the light-bulb change when the DC powered Primary coil is

moved slowly and then quickly towards the secondary coil. Explain in your lab report.

3. How does the voltmeter needle respond when the AC powered Primary coil is near the

secondary coil? When placed inside the secondary coil? Explain in your lab report.

• Part D – Electrical Power Generation:

1. How does the voltmeter respond when the bar magnet strength is increased from 50% to

100% at 10RPM? Explain in your lab report.

2. How does the voltmeter respond when the loop area is increased from 50% to 100% at

10RPM? Explain in your lab report.

3. How does the voltmeter respond when the water flow rate is increased to cause the

“turbine” to rotate fast from 10RPM to 50RPM? Explain in your lab report.

Lab Report:

• When writing the lab report, you must review and follow very carefully the Physics Lab Report

instructions and outline document.

• In your lab report, include the Title Page, Objectives, Theory, Equipment, Data, Graphs and

Screenshots, Calculations, Conclusions, Sources of Error, and References.

• Remember to show all equations and calculations in detail and to round the results to the correct

number significant digits and precision.

• In the conclusions section, be sure to summarize the final results, comment on the agreement

or disagreement of the results with the theory or expectations, answer analysis questions, and

discuss what you personally learned from this experiment and your observations/comments.

• Remember to also answer and discuss all analysis questions in your conclusions section.

• Submit your complete lab report electronically by the due date!

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Physics - Online Lab: Electromagnetic Induction

Tables of Data and Results

• Part A – Magnetic Field Lines and Field Strength:

Sketch the magnetic field around a bar magnet – show the magnetic field and the North/South

Pole directions.

( Your sketch the magnetic field around a bar magnet )

Magnetic Field Strength at 1 cm and 2 cm (50% and 100% Bar Magnet Strength)

Location of Magnetic Field Meter from North Pole of Bar Magnet

50% Bar Magnet Strength

100% Bar Magnet Strength

1 cm

2 cm

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• Part B – Induced Voltage/Current:

Record your observations of the relative “brightness” of the lightbulb as a function of the

change in the electromagnetic induction ‘Design” variables in Equations 1 and 2:

Light Bulb "Brightness" verses the Electromagnetic "Design" variables (Equations 1 and 2)

Variable Change Slow Magnet Motion Fast Magnet Motion

Coil Area 50%

Coil Area 100%

Magnetic Field Strength 50%

Magnetic Field Strength 100%

Number of Coils = 1

Number of Coils = 3

Record your observations of the voltmeter needle response to the bar magnet North and South

Pole movement towards and away from the coil:

Voltmeter Needle Response to the North and South Pole Magnet moving towards or away from the Coil

Magnet Pole and Movement Voltmeter Needle Response

North Pole Towards Coil

North Pole Away from Coil

South Pole Towards Coil

South Pole Away from Coil

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• Part C – Mutual Induction:

Record your observations of the relative “Brightness” of the lightbulb when the DC powered

Primary Coil is stationary or moved slowly/quickly through the Secondary coil:

Secondary Coil relative Brightness vs DC Powered Primary Coil Movement

Primary Coil Movement Light Bulb "Brightness"

No Movement

Slow Movement

Quick Movement

Record your observations of the AC Powered Primary coil’s effect on the Secondary Coil

Voltmeter response:

Secondary Coil Voltmeter Response vs AC Powered Primary Coil Location

Location of AC Powered Primary Coil relative to the Secondary Coil

Voltmeter Response Magnetic Field Change

Primary coil is to the left of the Secondary Coil

Primary Coil is inside the Secondary Coil

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• Part D – Electrical Power Generation:

Record your observations of the maximum voltage produced and movement direction of the

voltmeter needle as a function of bar magnet strength, coil area, and “Turbine” rotation rate:

Electrical Power Generation Vs. Bar Magnet Strength, Coil Area, and Turbine RPM

Location of AC Powered Primary Coil relative to the Secondary Coil

Voltmeter Maximum Value

Voltmeter Direction

Bar magnet strength 50%

Bar magnet strength 100%

Coil Area 50%

Coil Area 100%

Turbine 10 RPM

Turbine 50RPM