Lab 11: Solenoids
Objective: In this lab we will be calculating the magnetic field of a Solenoid using the method of
force balancing.
Set up: This lab consists of two separate circuits that combine into a single physical system. The
first circuit consists of the Solenoid in series with an ammeter and power supply. The second
circuit as a separate power supply, connected to the current balance and another ammeter. Do
not put more than 2A through either circuit.
Theory: The force felt through the far end of the current balance is:
๐น๐ต = ๐ผ๐ฟ๐ต
When mass is attached to the other end, there is a force due to gravity given by:
๐น๐ = ๐๐
We will be solving the magnetic field of the solenoid, which when balanced gives us:
๐ต = ๐๐
๐ผ๐ฟ
Procedure:
1. Verify which direction the magnetic field produced by the solenoid; you can do this by
inserting one end of current balance into the bore of the solenoid while a small current
is going through each circuit. The free end of the balance should move upward if the
field is directed the correct way. If not, switch the leads on one of the power supplies.
2. Turn the current on the solenoid off and affix (tying is easiest) your string to the free
end of the balance. Increase the current on the solenoid until the balance is level with
the table.
3. Repeat step 2 for 4 different lengths of string, recording solenoid current at each length.
Keep the current in the balance constant for each trial, if you must change it, record
doing so.
4. Solve for the magnetic field for each trial.
5. Now using the Pasco lab software with a Gaussmeter, measure the magnetic field
directly inside the solenoid.
6. Calculate % error of the B values you obtained from the balance against the measured
value.
Objective: In this lab we will be calculating the magnetic field of a Solenoid using the method of
force balancing.
Set up: This lab consists of two separate circuits that combine into a single physical system. The
first circuit consists of the Solenoid in series with an ammeter and power supply. The second
circuit as a separate power supply, connected to the current balance and another ammeter. Do
not put more than 2A through either circuit.
Theory: The force felt through the far end of the current balance is:
๐น๐ต = ๐ผ๐ฟ๐ต
When mass is attached to the other end, there is a force due to gravity given by:
๐น๐ = ๐๐
We will be solving the magnetic field of the solenoid, which when balanced gives us:
๐ต = ๐๐
๐ผ๐ฟ
Procedure:
1. Verify which direction the magnetic field produced by the solenoid; you can do this by
inserting one end of current balance into the bore of the solenoid while a small current
is going through each circuit. The free end of the balance should move upward if the
field is directed the correct way. If not, switch the leads on one of the power supplies.
2. Turn the current on the solenoid off and affix (tying is easiest) your string to the free
end of the balance. Increase the current on the solenoid until the balance is level with
the table.
3. Repeat step 2 for 4 different lengths of string, recording solenoid current at each length.
Keep the current in the balance constant for each trial, if you must change it, record
doing so.
4. Solve for the magnetic field for each trial.
5. Now using the Pasco lab software with a Gaussmeter, measure the magnetic field
directly inside the solenoid.
6. Calculate % error of the B values you obtained from the balance against the measured
value.
Data:
Current in
Balance
Mass of
string
Current in
Solenoid
Calculated B
field
Measured B
Field
% Error
Summary & Conclusion: Provide a brief summary of the experiment, discuss sources of error
and any other interesting observations you may have had.
Questions:
1. Derive the final expression from the theory section using torque instead of force.
2. What is the net force on the wires in the balance that run parallel to the solenoid?
3. Devise another way to run this experiment without using a mass on the other end of the balance, but still using a current balance.
4. Why must we wait until the balance is parallel with the table to calculate the magnetic field? If it was balanced (i.e. not moving) but at an angle, could we still find the magnetic field
