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Two long coaxial solenoids of unequal radii carry the same current I in the same sense. Let F₁ denote the magnetic force on the inner solenoid due to the outer solenoid, and F₂ denote the magnetic force on the outer solenoid due to the inner solenoid. Which statement is correct?

1. F₁ is directed radially inward and F₂ = 0
2. F₁ is directed radially outward and F₂ = 0
3. F₁ = F₂ = 0
4. F₁ is directed radially inward and F₂ is directed radially outward

Correct answer: F₁ = F₂ = 0

Solution

The magnetic fields inside coaxial solenoids do not exert forces on each other when they carry the same current in the same direction, resulting in zero net force on both solenoids.

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