Question

Two long ideal solenoids (with radii 20 mm and 30 mm respectively) have the same number of turns of wire per unit length. The smaller solenoid is mounted inside the larger, along a common axis. It is observed that there is zero magnetic field within the inner solenoid. The current in the inner solenoid must be: Select one: a. half the current in the outer solenoid b. twice the current in the outer solenoid c. the same as the current in the outer solenoid d. two-thirds the current in the outer solenoid e. one-third the current in the outer solenoid

          Two long ideal solenoids (with radii 20 mm and 30 mm
respectively) have the same number of turns of wire per unit
length. The smaller solenoid is mounted inside the larger, along a
common axis. It is observed that there is zero magnetic field
within the inner solenoid. The current in the inner solenoid must
be:
Select one:
a. half the current in the outer solenoid
b. twice the current in the outer solenoid
c. the same as the current in the outer solenoid
d. two-thirds the current in the outer solenoid
e. one-third the current in the outer solenoid

Added by Alicia D.

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