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 = Blv sinθ • calculate induced determine relative directions
• understand and of a loop in a magnetic field
• define inductance L
• define mutual
• appreciate that e.m.f. E = −N d dt
= −LdI 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 usingW = 12LI2 joules
• calculate inductance L of a coil, given L = N I
and L = N 2
S
• calculate mutual inductance using E2 = −M dI1dt andM = N1N2
S
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’. Figure 11.1(a) shows a coil of wire connected to a
centre-zero galvanometer, which is a sensitive ammeter with the zero-current position in the centre of the scale.
