Worksheet: The Magnetic Force between Parallel Constant Currents

In this worksheet, we will practice calculating the magnetic force between two parallel current-carrying wires.

Q1:

Two long, straight wires are parallel and 10 cm apart. One carries a current of 2.0 A, the other a current of 5.0 A. What is the magnitude of the force per unit length between the wires?

  • A 1 . 7 × 1 0 N/m
  • B 2 . 0 × 1 0 N/m
  • C 1 . 0 × 1 0 N/m
  • D 3 . 3 × 1 0 N/m
  • E 2 . 3 × 1 0 N/m

Q2:

The two long parallel wires shown in the figure carry currents in the same direction. If 𝐼=10 A and 𝐼=20 A, where 𝑎=60 cm, what is the magnetic field at point 𝑃?

  • A 2 . 8 × 1 0 T
  • B 3 6 × 1 0 T
  • C 7 . 8 × 1 0 T
  • D 6 . 8 × 1 0 T
  • E 4 . 8 × 1 0 T

Q3:

The figure shows two long, straight, horizontal wires that are parallel and a distance 2𝑎 apart, where 𝑎=30 cm. Both wires carry a current 𝐼=30 A, but in opposite directions.

What is the magnitude of the magnetic field at 𝑃?

What is the magnitude of the magnetic field at 𝑃

  • A 7 . 5 × 1 0 T
  • B 0 . 3 6 × 1 0 T
  • C 0 . 5 0 × 1 0 T
  • D 2 6 × 1 0 T
  • E 5 . 0 × 1 0 T

Q4:

Two long straight wires are parallel and 65 cm apart. If each wire carries a current of 80 A in the same direction, what is the magnetic force per unit length exerted on each wire?

  • A 2 . 0 × 1 0 N/m
  • B 8 . 4 × 1 0 N/m
  • C 6 . 3 × 1 0 N/m
  • D 9 . 1 × 1 0 N/m
  • E 1 . 6 × 1 0 N/m

Q5:

Two long parallel wires are hung by cords of length 4.00 cm, as shown in the figure. Each wire has a mass per unit length of 30.0 g/m and they carry the same current in opposite directions. What is the current if the cords are at a 6.00 angle with respect to the vertical?

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