Changing magnetic fields can induce electric potential differences.
Changing flux and the resulting induced potential difference is responsible for devices
ranging from transformers to magnetic brakes.
This connection of magnetism and electricity is responsible for some truly remarkable
Movement in magnetic field causes charge separation
To get a noticeable effect…
A shark is sensitive to a potential difference of 5 nV. If the shark’s head is 0.6 m wide,
and it swims at 2.0 m/s in a location where the dip angle is 60°…
What is the potential difference in the earth’s field?
ΔV = vlB
ΔV = (2.0 m/s) (0.6 m) (50 x 10 Tsin60°)
ΔV = 5.2 x 10 V
ΔV = 52000 nV
What is the smallest vertical field the shark can sense?
5 x 10 V = (2.0 m/s) (0.6 m) B
B = 4.2 nT
φ = A eff ABcosθ
θ is the angle between the magnetic field B and the axis of the loop.
The magnetic flux through the loop is φ = ABcosθ.
Lenz’s law There is an induced current in a closed, conducting loop if and only if the magnetic flux
through the loop is changing. The direction of the induced current is such that the
induced magnetic field opposes the change in the flux.
Changing flux induces an emf
An emf ε is induced in a conducting loop if the magnetic flux