Chapter14 : Electromagnetism

Example No. 14_1 Page No. 421

In [1]:
# Calculate the ampere-turns of mmf for a coil with 2000 turns and a 5-mA current.

# Given data

I = 5*10**-3#        # Current=5 mAmps
N = 2000#           # No. of Turns=2000

mmf = I*N#
print 'The Amps-Turn (A.t) of Magneto-Motive Force (mmf) = %0.2f A.t'%mmf

The Amps-Turn (A.t) of Magneto-Motive Force (mmf) = 10.00 A.t

Example No. 14_2 Page No. 421

In [2]:
# A coil with 4 A is to provide a magnetizing force of 600 A t. How many turns are necessary?

# Given data

I = 4#        # Current=4 Amps
mmf = 600#    # Magnetizing Force=600 A.t

N = mmf/I#
print 'The Turns necessary are : ',N

The Turns necessary are :  150

Example No. 14_3 Page No. 424

In [3]:
# A coil with 400 turns must provide 800 A t of magnetizing force. How much current is necessary?

# Given data

mmf = 800#    # Magnetizing Force=800 A.t
N = 400#      # No. of Turns=400

I = mmf/N#
print 'The Current necessary = %0.f Amps'%I

The Current necessary = 2 Amps

Example No. 14_4 Page No. 426

In [4]:
# The wire in a solenoid of 250 turns has a resistance of 3 Ohms. (a)How much is the current when the coil is connected to a 6-V battery? (b) Calculate the ampereturns of mmf.

# Given data

V = 6#             # Voltage=6 Volts
R = 3#             # Resistance=3 Ohms
N = 250#           # No. of Turns=250

I = V/R#
print 'The Current necessary when a wire is connected to 6-V Battery = %0.f Amps'%I

mmf = I*N#
print 'The Amps-Turn (A.t) of Magneto-Motive Force (mmf) = %0.f A.t'%mmf

The Current necessary when a wire is connected to 6-V Battery = 2 Amps
The Amps-Turn (A.t) of Magneto-Motive Force (mmf) = 500 A.t

Example No. 14_5 Page No. 426

In [7]:
# A magnetic material has a ur of 500. Calculate the absolute u as B/H (a) in CGS units and (b) in SI units.

# Given data

ur = 500#         # ur=500
uoa = 1#          # uo for CGS Units=1
uob = 1.26*10**-6# # uo for SI Units=1.26 u

ua = ur*uoa#
print 'The Absolute u as B/H in CGS = %0.f (G/Oe)'%ua

ub = ur*uob#
print 'The Absolute u as B/H in SI = %0.3e (T/(A.t/m))'%ub
print 'i.e 630*10**-6 T/(A.t/m)'

The Absolute u as B/H in CGS = 500 (G/Oe)
The Absolute u as B/H in SI = 6.300e-04 (T/(A.t/m))
i.e 630*10**-6 T/(A.t/m)

Example No. 14_6 Page No. 427

In [8]:
# u = 630*10**-6 in SI units, calculate the flux density B that will be produced by the field intensity H equal to 1000 A.t/m.

# Given data

u = 630*10**-6#      # u=630 micro T/(A.t/m)
H = 1000#           # H=1000 A.t/m

B = u*H#
print 'The Flux density = %0.2f Tesla'%B

The Flux density = 0.63 Tesla