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)

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. $F.B.D$

${\vec{F}}_1=0$
${\vec{F}}_2=0$