Question

1 a) A certain tightly-wound coil of wire is perpendicular to an external magnetic field. The...

1 a) A certain tightly-wound coil of wire is perpendicular to an external magnetic field. The magnetic field has a strength of 3.4 mT, and the coil is circular with a radius of 10.7 cm. If I run a current of 4.5 A through the wire (in the right direction), I can cause the net flux through the coil to be zero. If the coil has 26 turns, what is its inductance? Express your answer in mH (millihenrys).

b) An RL circuit has L = 1.2 H and R = 3.6 Ω. If a battery has been connected to the circuit and you remove it, how long will it take for the voltage across the resistor to fall to 11% of its starting value? Express your answer in seconds.

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Homework Answers

Answer #1

1)magnetic field due to coil = external magnetic field

flux density B= 0 x N xI /length =3.4x10-3 T

length = 4x10-7 x26x4.5 /3.4x10-3  = 0.0432metre

inductance L = 0 x N2 xA / Length  = 4x10-7 x262 x x0.1072 /0.0432= 0.707mHenry

L=1.2H R=3.6ohm

2) i = I0 x e-(R/L) t1    equation---1

0.11x i =I0 x e-(R/L) t2    equation---2 put R/L =3.6/1.2 =3

divide equation-2 /  equation1 = 0.11 = e-(3t2 - 3t1)

0.735 = t2 - t1  

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