266 Chapter 8 Magnetic Fields and Electromagnetism Copyright © 2003 Nelson

Instructional Master

Faraday’s Ring

LSM 8.5-1

secondary coil

primary coil

wooden core galvanometer

switch

battery

Figure 1Faraday’s first induction apparatus. There are two separate circuits. Charges do notpass from the primary circuit into the secondary circuit.

primary

ironcore

secondary

I

Primary circuitis turned on.

Primary circuitis turned off.

t (s)

I (m

A)

Current in Secondary Circuit

Figure 2Only when the primary circuit is turned on and off is acurrent induced in the secondary circuit. There is nocurrent in the secondary circuit when the current in theprimary circuit is constant. The plot shows the two cur-rents to be in opposite directions.

Figure 3Faraday’s iron ring. Even though the magnetic fields arestronger than in Faraday’s first apparatus, an inducedcurrent is produced in the secondary circuit only whenthe primary circuit is turned on or off, changing themagnetic field.