ABSTRACT
At the end of this chapter you should be able to: • understand how an e.m.f. may be induced in a conductor
• state Faraday’s laws of electromagnetic induction • state Lenz’s law • use Fleming’s right-hand rule for relative directions • appreciate that the induced e.m.f., E =Blv or
E =Blv sin θ • calculate induced e.m.f. given B, l, v and θ and determine relative directions
• understand and perform calculations on rotation of a loop in a magnetic field
• define inductance L and state its unit • define mutual inductance • appreciate that e.m.f. E =−N d
dt =−L dI
dt
• calculate induced e.m.f. given N , t, L, change of flux or change of current
• appreciate factors which affect the inductance of an inductor
• draw the circuit diagram symbols for inductors • calculate the energy stored in an inductor using
W = 12LI2 joules • calculate inductance L of a coil, given L= N
I and
L= N 2
S • calculate mutual inductance using E2 =−MdI1dt and
M = N1N2 S
9.1 Introduction to electromagnetic induction
When a conductor is moved across a magnetic field so as to cut through the lines of force (or flux), an electromotive force (e.m.f.) is produced in the conductor. If the conductor forms part of a closed circuit then the e.m.f. produced causes an electric current to flow round the circuit. Hence an e.m.f. (and thus current) is ‘induced’ in the conductor as a result of its movement across the magnetic field. This effect is known as ‘electromagnetic induction’.
