3. A coil of wire with 80 turns has a cross-sectional area of 0.04 m2. A magneti
ID: 2041103 • Letter: 3
Question
3. A coil of wire with 80 turns has a cross-sectional area of 0.04 m2. A magnetic field of 0.6 T passes through the coil. a) What's the total magnetic flux passing through the coil? b) If the magnetic field disappears in 0.2 seconds, what's the average voltage induced in the coil (electromotive force)? 4. A step-down transformer is to be used to convert an ac voltage of 120 V to 6 V to power an electric train. If there are 300 turns in the primary coil, how many turns should there be in the secondary coil?Explanation / Answer
3) given
N = 80 turns
A = 0.04 m^2
B = 0.6 T
a) tota magnetic flux through the coil = N*A*B
= 80*0.04*0.6
= 1.92 Weber or T.m^2
b) induced emf = change magnetic flux/time taken
= (1.92 - 0)/0.2
= 9.6 V
4)
given
Vp = 120 V
Vs = 6 V
Np = 300 turns
Ns = ?
use, tranformer equation
Vs/Vp = Ns/Np
6/120 = Ns/300
==> Ns = 300*(6/120)
= 15 turns