Force between Parallel Currents — Prelims Questions

Two long and parallel straight wires A and B carrying currents of $5,\text{A}$ and $10,\text{A}$ respectively in the same direction are separated by a distance of $0.1,\text{m}$. What is the force per unit length experienced by wire B due to wire A?

Two parallel wires, P and Q, are separated by a distance $r$. Wire P carries a current $I$ into the page, and wire Q carries a current $2I$ out of the page. What is the nature of the force between them?

Three long, straight, parallel wires A, B, and C are placed in the same plane. Wire B is between A and C. The distance between A and B is $d_1$, and between B and C is $d_2$. Wires A and C carry current $I$ in the same direction, while wire B carries current $2I$ in the opposite direction. What is the net force per unit length on wire B?

Two long parallel wires carrying currents $I_1$ and $I_2$ are separated by a distance $d$. If the current $I_1$ is doubled and the distance $d$ is halved, what happens to the force per unit length between them?

Which of the following statements is INCORRECT regarding the force between two long parallel current-carrying wires?

Two long parallel wires are separated by $4,\text{cm}$. If they carry currents of $3,\text{A}$ and $5,\text{A}$ respectively in opposite directions, what is the force per unit length between them?