1. The pole face of a magnet is 3 cm by
2 cm and it produces a flux of 30µWb. Calculate the flux density at the pole
face.
A = 3 x 2 x 10-4 m2; ɸ = 30 x 10-6
Answer:
B = ɸ/A
= 30 x 10-6 / 6 x 10-4
= 0,05 tesla
= 50 mT
2. Calculate the excitation current
required in a 600 turn coil in order to produce an mmf of 1500 At.
N = 600 ; F = 1500 At
Answer:
F = NI
I = F/N
= 1500/600
= 2.5 A
3. A 1500 turn coilis uniformly wound
araound an iron toroid of uniform csa 5 cm2. Calculate mmf and flux density producedif the resulting flux is
0.2 mWb when the coil current is 0.75 A.
N = 1500; A = 5 x 10-4 m2; ɸ = 0,2 x 10-3Wb; I=0.75 A
Answer:
F = NI
= 1500 x 0.75
= 1125 At
B = ɸ / A
= 0.2 x 10-3 / 5 x 10-4
= 0.4 T
4. A current of 400 mA is passed through
a 550 turn coil wound on a toroid of mean diameter 8 cm.
I = 0,4 A ; N = 550 ; d = 8 x 10-2 m
Answer:
Ɩ = πd
= 3,14 x 8 x 10-2
= 0,251 m
H = NI / Ɩ
= 550 X 0,4 / 0.251
= 875.35 At/m
5. An iron toroid having a mean radius
of 0.1 m and csa of π cm2 is wound with a 1000 turn coil the coil
current results in a flux of 0.1775 mWb in the toroid . using the following
data, determine
a. The coil current and
b. The relative permeability of the
toroid under these conditions.
H(At/m) 80 85 90 95 100
B(T) 0.5 0.55 0.58 0.59 0.6
Answer:
B = ɸ / A
= 0.1775 x 10-3 / π x
10-4
= 0.565 T
And from the plotted graph, when B = 0.565T, H = 88 At/m
a. Now, the lengt of the toroid, Ɩ = 2πr
= 0.628 m
H = NI / Ɩ
I = HƖ / N
= 88 x 0.628 / 1000
= 0.0553 A
= 55.3 Ma
b. B
= µ0µr H
µr = B / µOH
= 0.565 / 4π x 10-7 x 88
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