1) DIRECTION OF THE MAGNETIC FIELD: The direction of the field of acoil or solen

Question

1) DIRECTION OF THE MAGNETIC FIELD: The direction of the field of acoil or solenoid along the axis can be determined by the right-handrule. If you wrap the fingers of your right hand in the directionof the current, your thumb will point in the direction of themagnetic field.

a) For a coil with 13 turns, a radius 9.7 cm, and a current of 6.4A, what is the field at the center of the coil?

b) A slinky with length 20. cm and 45 turns has a current of 960 mArunning through it. What is the magnetic field near the center ofthe slinky?

A) 2.71E-04 T
B) 5.43E-02 T
C) 5.43E-05 T
D) 2.71E-01 T

c) A solenoid with n turns per unit length has a currentI flowing through it. If the solenoid is made longerwithout changing the number of turns or without changing thecurrent, what happens to the field?

A) It will remain the same.
B) It will increase.
C) It will decrease.

Explanation / Answer

For part a. and b.   use   B =0 N I / L     where N isthe number of turns a.   B = 4 x 10-7 * 13 * 6.4 A /0.097 m          =0.0011 T b.   B = 4 x 10-7 * 45* 0.960 A / 0.20 m          = 0.000271 T    --> chooseA                                c.   We can rewrite the formula as B =0 n I    if we want 'n' forthe turns per unit length (n = N / L) If the length 'L' increases, the turns per unit length 'n'decreases (since 'N' is constant). So the solenoid becomesweaker, i.e. B decreases

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