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Lesson: The Magnetic Force between Parallel Constant Currents

In this lesson, we will learn how to calculate the magnetic force between two parallel current-carrying wires.

Sample Question Videos

02:02

Worksheet • 5 Questions • 1 Video

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 2 . 0 × 1 0 − 5 N/m
  • B 3 . 3 × 1 0 − 5 N/m
  • C 1 . 0 × 1 0 − 5 N/m
  • D 2 . 3 × 1 0 − 5 N/m
  • E 1 . 7 × 1 0 − 5 N/m

Q2:

The two long parallel wires shown in the figure carry currents in the same direction. If 𝐼 = 1 0 1 A and 𝐼 = 2 0 2 A, where 𝑎 = 6 0 cm, what is the magnetic field at point 𝑃 ?

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

Q3:

The figure shows two long straight horizontal wires that are parallel and a distance 2 𝑎 apart, where 𝑎 = 3 0 cm. Both wires carry a current 𝐼 = 3 0 A but in opposite directions.

What is the magnitude of the magnetic field at 𝑃 1 ?

What is the magnitude of the magnetic field at 𝑃 2

  • A 5 . 0 × 1 0 − 6 T
  • B 0 . 5 0 × 1 0 − 6 T
  • C 2 6 × 1 0 − 6 T
  • D 0 . 3 6 × 1 0 − 6 T
  • E 7 . 5 × 1 0 − 6 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 − 3 N/m
  • B 1 . 6 × 1 0 − 2 N/m
  • C 6 . 3 × 1 0 − 3 N/m
  • D 9 . 1 × 1 0 − 3 N/m
  • E 8 . 4 × 1 0 − 3 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 . 0 0 ∘ angle with respect to the vertical?
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