Lab 7 Magnetic Induction
Introduction
We will examine Faraday’s law or the effects of changing magnetic fields on a conducting coil.
Equipment
Power supply, DMM, rheostat, solenoid, compass.
Background
Faraday’s law expresses the relationship between the magnetic flux through an area to the current
and voltage (emf) induces in the boundary of that area.
I or V(emf ) = −N
ΔΦmagnetic
Δt
Experiment: Set Up
Set up the primary coil in series with the rheostat and pass a 1 A of current through it. Set up the
secondary coil face to face with the primary coil and connect a DMM to it set to the milliampere
current mode. Make sure that the wires in both coils rotate in the same direction.
to power supply
primary coil
to DMM
secondary coil
Experiment: Turning On the Primary Coil
With the power off, turn the power on and instantly pay attention to the ammeter. Record the
direction of the current in the primary coil based on how you built the circuit. Record the direction
of the current in the secondary coil based on the ammeter reading.
turn on and off
primary coil
secondary coil
Using the following diagrams, indicate the following quantities as the current in the secondary coil
is increasing toward the maximum current magnitude. Make sure everyone is looking at the coils
from the same perspective.
page 1
1. What is the directions of the current in the primary coil based on your observation? Draw an
arrow around the coil.
primary coil
secondary coil
2. What is the magnetic field directions in the primary coil? Use the “in” or “out” directions.
primary coil
secondary coil
3. In what direction is the magnetic flux through the primary coil increasing? Use the “in” or “out”
directions.
primary coil
secondary coil
4. In what direction is the magnetic flux through the secondary coil increasing from the effect of
the primary coil? Use the “in” or “out” directions.
primary coil
secondary coil
5. What is the magnetic field directions in the secondary coil from the effect of the primary coil?
Use the “in” or “out” directions.
primary coil
secondary coil
6. What is the directions of the current in the secondary coil based on your observation? Draw
an arrow around the coil.
primary coil
secondary coil
7. What is the magnetic field directions in the secondary coil from the current in the secondary
coil? Use the “in” or “out” directions.
primary coil
secondary coil
8. Does your answer for (5) opposite of the answer for (7)?
page 2
Experiment: Turning Off the Primary Coil
Repeat the above experiment. However, start with the power already on, turn the power off and
instantly pay attention to the ammeter. Record the direction of the current in the primary coil
based on how you built the circuit. Record the direction of the current in the secondary coil based
on the ammeter reading.
1. What is the directions of the current in the primary coil based on your observation? Draw an
arrow around the coil.
primary coil
secondary coil
2. What is the magnetic field directions in the primary coil? Use the “in” or “out” directions.
primary coil
secondary coil
3. In what direction is the magnetic flux through the primary coil increasing? Use the “in” or “out”
directions.
primary coil
secondary coil
4. In what direction is the magnetic flux through the secondary coil increasing from the effect of
the primary coil? Use the “in” or “out” directions.
primary coil
secondary coil
5. What is the magnetic field directions in the secondary coil from the effect of the primary coil?
Use the “in” or “out” directions.
primary coil
secondary coil
6. What is the directions of the current in the secondary coil based on your observation? Draw
an arrow around the coil.
primary coil
secondary coil
7. What is the magnetic field directions in the secondary coil from the current in the secondary
coil? Use the “in” or “out” directions.
primary coil
secondary coil
8. Does your answer for (5) opposite of the answer for (7)?
page 3
Experiment: Moving the Primary Coil Away
Now, repeat the experiment with the primary coil on and move the primary coil away from the
secondary coil. Record the direction of the current in the primary coil based on how you built the
circuit. Record the direction of the current in the secondary coil based on the ammeter reading.
on
primary coil
move away
secondary coil
1. What is the directions of the current in the primary coil based on your observation? Draw an
arrow around the coil.
primary coil
secondary coil
2. What is the magnetic field directions in the primary coil? Use the “in” or “out” directions.
primary coil
secondary coil
3. In what direction is the magnetic flux through the primary coil increasing? Use the “in” or “out”
directions.
primary coil
secondary coil
4. In what direction is the magnetic flux through the secondary coil increasing from the effect of
the primary coil? Use the “in” or “out” directions.
primary coil
secondary coil
5. What is the magnetic field directions in the secondary coil from the effect of the primary coil?
Use the “in” or “out” directions.
primary coil
secondary coil
6. What is the directions of the current in the secondary coil based on your observation? Draw
an arrow around the coil.
page 4
primary coil
secondary coil
7. What is the magnetic field directions in the secondary coil from the current in the secondary
coil? Use the “in” or “out” directions.
primary coil
secondary coil
8. Does your answer for (5) opposite of the answer for (7)?
Experiment: Moving the Primary Coil Closer
Now, repeat the experiment with the primary coil on and move the primary coil toward from the
secondary coil. Record the direction of the current in the primary coil based on how you built the
circuit. Record the direction of the current in the secondary coil based on the ammeter reading.
on
primary coil
move closer
secondary coil
1. What is the directions of the current in the primary coil based on your observation? Draw an
arrow around the coil.
primary coil
secondary coil
2. What is the magnetic field directions in the primary coil? Use the “in” or “out” directions.
primary coil
secondary coil
3. In what direction is the magnetic flux through the primary coil increasing? Use the “in” or “out”
directions.
primary coil
secondary coil
4. In what direction is the magnetic flux through the secondary coil increasing from the effect of
the primary coil? Use the “in” or “out” directions.
page 5
primary coil
secondary coil
5. What is the magnetic field directions in the secondary coil from the effect of the primary coil?
Use the “in” or “out” directions.
primary coil
secondary coil
6. What is the directions of the current in the secondary coil based on your observation? Draw
an arrow around the coil.
primary coil
secondary coil
7. What is the magnetic field directions in the secondary coil from the current in the secondary
coil? Use the “in” or “out” directions.
primary coil
secondary coil
8. Does your answer for (5) opposite of the answer for (7)?
page 6