Force between parallel conductors; definition of the ampere — NEET & JEE Questions

Question 1 · difficulty L1 · recall

Two long parallel wires carrying currents in the same direction

• A. attract each other
• B. repel each other
• C. exert no force
• D. alternate between attraction and repulsion

Question 2 · difficulty L1 · understanding

Two long parallel wires carrying currents in opposite directions

• A. attract each other
• B. repel each other
• C. exert no force
• D. must twist but not translate

Question 3 · difficulty L2 · understanding

The force per unit length between two long parallel wires separated by d and carrying currents I1 and I2 is

• A. μ0I1I2/(4πd²)
• B. μ0I1I2d/(2π)
• C. μ0I1I2/(2πd)
• D. μ0(I1+I2)/(2πd)

Question 4 · difficulty L2 · application

If the separation between two parallel current-carrying wires is doubled while currents are unchanged, the force per unit length becomes

• A. twice
• B. one-fourth
• C. unchanged
• D. one-half

Question 5 · difficulty L2 · understanding

Two long parallel wires carrying currents in the same direction exert forces on each other that are

• A. attractive
• B. repulsive
• C. zero in every case
• D. independent of current direction

Question 6 · difficulty L3 · application

If both currents in two parallel wires are doubled at fixed separation, their force per unit length becomes

• A. four times
• B. twice
• C. half
• D. unchanged

Question 7 · difficulty L3 · application

In the traditional force-based definition, two 1 A currents in parallel conductors 1 m apart in vacuum produce a force per metre of

• A. 2 × 10^-6 N m^-1
• B. 2 × 10^-7 N m^-1
• C. 4π × 10^-7 N m^-1
• D. 1 × 10^-7 N m^-1

Question 8 · difficulty L3 · application

Two long parallel wires carry currents $I_1$ and $I_2$ and are separated by distance d. The force per unit length is proportional to

• A. $I_1I_2/d$
• B. $I_1+I_2$
• C. $d/(I_1I_2)$
• D. $I_1I_2d$

Question 9 · difficulty L3 · application

If both currents in two parallel wires are doubled while their separation remains unchanged, the force per unit length becomes

• A. four times
• B. twice
• C. half
• D. unchanged

Question 10 · difficulty L4 · analysis

Three identical long parallel wires carry equal currents in the same direction and are equally spaced in a straight line. The net force on the middle wire is

• A. toward the left wire
• B. toward the right wire
• C. zero
• D. twice the force from one neighbour