Practice question · True or false
An Amperian loop drawn entirely outside a long solenoid encloses zero net current, so the field just inside the solenoid must be zero.
Hints
- What quantity does Ampere’s law actually constrain?
- It constrains the circulation round the loop, not the field at other points.
Show the answer
False
Why
False, the loop outside encloses equal and opposite currents from the two sides of the winding, so its circulation vanishes. That says nothing about the field elsewhere, and inside the solenoid the field is large and uniform.
Practise Magnetostatics in Vacuum
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