I. Magnetic Fields and Induced EMF
November 14, 2018
II. Abstract
The objective of this lab was to observe electromotive forces created by a varying
magnetic field in a coil. This was done by spinning a magnet on a rod past a coil sensor
bundle which sent data to the datastudio program and data was obtained from the graph
displayed. This data is shown for part one of the lab which resulted in an observed number of
2m^2. This value does verify the laws being tested as shown by the error range:
0.8626m2≤1.7251m2≤2.5877m2 . The value of 2m^2 is found within this range. For
part two of the lab, the magnet was spun until it came to a complete stop. The data found on
the graph displayed by the datastudio program was used to find the values needed. The last
10 values displayed were used to find the derivative of the graph which yielded the velocity.
The value of the velocities and the induced EMF were graphed, and the slope was calculated
to determine if the lab verified the law being tested. The error range found was:
0.021879m≤0.04376 m≤0.065639m . The slope value found was 0.0244 m*T which was
also found within the given slope range.
III. Theory
Electromotive forces (EMFs) are mechanisms that allow for the conversion of forms of
energy. Things such as batteries, photo-voltaic cells, or generators, are known to use energy in a
stored form. EMF produces a potential energy between two points called terminals. Terminals
are shown with a positive or negative sign based on the flow of the circuit. When terminals are
connected, it allows the circuit to move, which starts the energy conversion process to produce a
current. Magnetic fields and conductors can produce EMF’s. Changes in dimension of the loop
will cause a current to be produced. The magnitude of the magnetic field can change while the
size of the loop is constant. A current will also be produced. Flux is defined as the number of
field lines that pass through the cross section, if the area changes or magnetic field change, then
the flux also changes. The equation for EMF is ε=-N∗π∗r2∗∆ B
∆t
, where N is the number
of turns within the coil, and r2 is the inner radius squared. ∆B
∆t represents the change in
magnetic field strength over time.
IV. Objective
The objective of this lab is to observe electromotive forces created by a varying magnetic
field in a coil.
V. Procedure
The experiment began with setting up the equipment as shown below. Then, the box was
turned on before the computer. Datastudio was run with the “induction2.ds” activity and a
magnet was spun on the rod so that it quickly passed the coil-sensor bundle. Recordings of the
signal were taken by the sensor and displayed on data studio.
First, the graph of the recordings was created and zoomed in on the single peak in the
magnetic field while the EMF graph was locked into the same time axis. A printout of the
computer screen was made with the B field, EMF and derivative of the B field traces on it.