A little solenoid electromagnet is 110mm long and 30mm diameter ; it has 30? res
ID: 1262595 • Letter: A
Question
A little solenoid electromagnet is 110mm long and 30mm diameter ; it has 30? resistance and inductance 90mH (with an iron rod in it).
is powered it with 4 dry cells (6V) with a switch.
. . . a) Calculate the current that should have been flowing in the solenoid long after the switch was closed.
. . . b) Calculate the solenoid Area, and determine the magnetic field that it must have been producing.
. . . surprised? that is with the iron rod filling its core ... its inductance is 1/9 as much without the iron rod.
. . . c) using its resistance and its inductance, how long should it have taken for the current to rise to 125mA?
. . . d) if its B
Explanation / Answer
A)
supply voltage=6v
inductance XL=2*3.14*50*90*10-3
=28.26OHMS
R=30OHMS
Z=30+j28.26
=41.21ohms
I=V/Z
=6/41.21
=0.1455A
B)
L=mu*N2*A/L
A=3.14*900*10-6/4
=706.5*10-6m2
90*10-3=80.66*10-16*N2
N=3.34*106TURNS
N*PI=LI
=90*10-3*0.1455
=13.095/3.34*106
=3.92*10-6
flux=BA
B=3.92*10-6/706.5*10-6
=5.54mT
C)
time constant of circuit=L/R
=90/30
=3milliseconds
flux=BA
=0.1125wb
induced emf=0.1125/3
=0.0375*103VOLTS
=37.5volts
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