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I came across this when doing my revision exam paper and had this doubt. I wanted to ask whether a solenoid will expand radially outwards when current flows through it.

(The actual question was whether the solenoid will expand/contract linearly. The answer was that it would expand/contract linearly as current of the same direction flows through the wire.)

Original exam question: 1

My working: 2

Surprisingly, the answer is D.

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Your question and the picture don't seem to be about the same topic (radial versus longitudinal).

Here are the facts:

The solenoid will contract linearly (get shorter) as the wires in adjacent turns are carrying current in the same direction and parallel current attract. At the same time the solenoid will tend to expand radially (get fatter) as the currents on the opposite side of the coil are in the opposite direction and opposite (antiparallel) currents repel.

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  • $\begingroup$ thank you @mike stone , yess i messed up my question put my question was : to find whether solenoid expands radially or not. i did some working and posted the picture for same. thanks a lot $\endgroup$
    – mr.anonymous
    Commented Sep 6, 2021 at 13:03
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The right hand rules predict that the turns of wire near the ends of a current carrying solenoid will be pushed toward the center by the converging (or diverging) field at the ends. If the axis of the solenoid is horizontal, then the segments of wire on the top will be pushed up by the field from segments on the bottom.

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  • $\begingroup$ I am not able to understand your point. $\endgroup$
    – mr.anonymous
    Commented Sep 6, 2021 at 17:15
  • $\begingroup$ could you please elaborate $\endgroup$
    – mr.anonymous
    Commented Sep 6, 2021 at 17:15
  • $\begingroup$ My statements pretty much agree with those from Mike Stone, except that the coils toward the center of a current carrying solenoid are pulled in both directions by adjacent turns on each side. The longitudinal contractions occur only near the ends. $\endgroup$
    – R.W. Bird
    Commented Sep 6, 2021 at 18:58

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