Question

Two coaxial solenoids of different radii carry current $I$ in the same direction. Let $\vec{F}_1$ be the magnetic force on the inner solenoid due to the outer one and $\vec{F}_2$ be the magnetic force on the outer solenoid due to the inner one. Then,

• A. $\vec{F}_1$ is radially outwards and $\vec{F}_2$ = 0
• B. $\vec{F}_1$ is radially inwards and $\vec{F}_2$ is radially outwards
• C. $\vec{F}_1$ is radially inwards and $\vec{F}_2$ = 0
• D. $\vec{F}_{1} = \vec{F}_2 = 0$

Answer 1

Answer: (D)

$\vec{F}_{1} = \vec{F}_2 = 0$

Answer 2

Cross-sectional view (Both solenoids are taken to be ideal in nature.) Both wires will attract each other, but net force on each wire will be zero. Concept: Two current carrying elements attract each other if direction of current is same. $F.B.D$ $\vec{ F }_{1}=0$ $\vec{ F }_{2}=0$