1. Objective
The aim of this experiment is to learn how a permanent magnet, a moving coil with a constant
current, and a constant coil with a changing current, change the induced voltage in a coil.
2. Description
The apparatus used in this lab includes Capstone, RLC circuit board, box with 2 coils that has
iron rod and a cylindrical magnet, 1 voltage sensors, 2 leads (120 cm.), and 1 lead (150-200 cm).
In this experiment an emf was induced in one coil by moving a permanent magnet into and out of
the coil, moving a second coil, which has a current, near the first coil, and changing the current
in the second coil. Most of the results were be qualitative. The strength of the induced emf
depends on the rate of change of the magnetic field. When an emf is induced in a coil the current
that results will depend on the resistance of the circuit which the coil is part of. A voltage will
also appear across the coil which was measured by a voltmeter.
3. Theory
The changing magnetic field produces an electric field which is not conservative. The line
integral of the electric field around a loop or circuit is not zero and is called an electromotive
force or EMF. The EMF can drive a current in a circuit. The unit of EMF is the volt (V). The flux
Φ of the magnetic field is defined in a similar way to the flux of the electric field. A magnetic
field vector ⃗ B passes through a differential area d ⃗A . The differential element of magnetic
flux associated with d ⃗A is dΦ = ⃗ B · d ⃗A . It is only the component of ⃗ B that is
perpendicular to the surface area that contributes to the flux. For a finite area the magnetic flux is
Φ = ∫⃗ B · d ⃗A . The line integral of the electric field around the boundary of the area is
called EMF (voltage). The positive directions of d ⃗A and the line integral must be consistent
with the right hand rule where the thumb points in the direction of d ⃗A . Faraday’s law says
that for a single circuit around the boundary of the area the EMF= -dΦ/dt. The non-conservative
electric field giving rise to the emf exists whether there is a wire around the boundary or not. A
current will flow as long as the circuit is complete, and will be limited by the resistance of the
circuit. If the loop of wire has two ends then a voltage of V = +dΦ/dt will appear between those
two ends. This voltage is due to a conservative electric field that opposes the non-conservative
electric field producing the EMF. If the wire has N complete turns it is called a coil. The voltage
across a coil is equal to the number of wire turns (N) multiplied by Faraday’s law, V