Lab #6: Faraday’s Law
Theory:
• State Faraday’s Law.
• How the EMF induced in a coil is calculated?
• Magnetic flux through a loop.
Experiment:
Primary coil → big coil (outer)
Secondary coil → small coil (inner)
The changing current in a primary coil (I) will induce a changing magnetic field in the
primary coil and changing magnetic flux in a secondary coil.
Φ s = B p ⋅ As
where As is cross sectional area of the secondary coil and Bp magnetic field of primary
coil.
That changing current in a primary coil induces EMF in a secondary coil ( ε meas )
dΦ s
dI
ε calc = − N s
= − N s As µ 0 n p
dt
dt
where Ns=(235±1)turn – number of turns in secondary coil
As=πr2 - cross sectional area of a secondary coil
D + Din Dout − Din
r=D/2; D = out
±
2
2
−7
2
µ 0 = 12.57 x10 N / A - permeability of free space
N p # ofturn sin primarycoil
np =
=
Lp
lengthofaprimarycoil
Np=(2920±1)turn
1. Measure length of the primary solenoid, Lp, and outer and inner diameter of
secondary solenoid, Douter and Dinner , using the caliper
2. Measure the resistance of the primary coil, Rp using DMM
3. Place the smaller (secondary) solenoid into the larger (primary) and follow the
procedure.
Data Analysis:
1. Determine dI/dt:
a) Transfer output voltage data from the oscilloscope to a graph
b) Find the slope of V vs. t
c) dI/dt is the slope divided by the resistance of the primary coil, Rp
2. Red line is the output voltage from the amplifier to the primary coil and green
is voltage induced in secondary coil (εmeas). Compare εmeas with εcalc