JEE Main 2014 · 11 Apr · Shift 1 · Physics Q19

PhysicsSingle correct+4 / -1Question 19 of 90

Three straight parallel current carrying conductors are shown in the figure. The force experienced by the middle conductor of length 25 cm is :

3\times10^{-4}

N toward right

6\times10^{-4}

N toward left

9\times10^{-4}

N toward left

Zero

Answer and worked solution

Official answer: A

Antiparallel currents repel; per unit length $\dfrac FL=\dfrac{\mu_0I_aI_b}{2\pi d}$ .

From $I_1$ (3 cm, pushes right): $\dfrac{2\times10^{-7}\times30\times10}{0.03}=2\times10^{-3}$ N/m.
From $I_2$ (5 cm, pushes left): $\dfrac{2\times10^{-7}\times20\times10}{0.05}=8\times10^{-4}$ N/m.

Net $1.2\times10^{-3}$ N/m to the right. Over 0.25 m: $3\times10^{-4}$ N toward the right.

JEE Main 2014 · 11 Apr · Shift 1, Physics question 19