Worksheet: Magnetic Field due to a Long Straight Conductor Carrying a Constant Current

In this worksheet, we will practice calculating the magnitude of the magnetic field produced by a long straight current-carrying wire at a given distance from the wire.

Q1:

The magnitude of the magnetic field 50 cm from a long, thin, straight wire is 8.0 µT. What is the current through the long wire?

Q2:

A long, straight, horizontal wire carries a left-to-right current of 20 A. If the wire is placed in a uniform magnetic field of magnitude 4 . 0 × 1 0 5 T that is directed vertically downward, what is the resultant magnitude of the magnetic field 20 cm above the wire?

  • A 4 . 0 × 1 0 5 T
  • B 3 . 3 × 1 0 5 T
  • C 5 . 0 × 1 0 5 T
  • D 4 . 5 × 1 0 5 T
  • E 6 . 7 × 1 0 5 T

Q3:

A typical current in a lightning bolt is 4 . 0 × 1 0 4 A. Estimate the magnetic field 5.0 m from the bolt.

  • A 4 . 2 × 1 0 3 T
  • B 3 . 2 × 1 0 3 T
  • C 9 . 6 × 1 0 3 T
  • D 1 . 6 × 1 0 3 T
  • E 1 6 × 1 0 3 T

Q4:

A transmission line strung 3.00 m above the ground carries a current of 335 A. What is the magnetic field on the ground directly below the wire?

  • A 1 . 3 6 × 1 0 3 T
  • B 6 3 6 0 × 1 0 3 T
  • C 0 . 3 6 9 × 1 0 6 T
  • D 2 . 2 4 × 1 0 5 T
  • E 4 . 4 8 × 1 0 5 T

Q5:

The figure shows two long straight horizontal wires that are parallel and a distance 2 𝑎 apart, where 𝑎 = 3 0 cm. If the wires carry currents 𝐼 = 2 0 1 A and 𝐼 = 3 0 2 A, in opposite directions, at what distance between them from the top wire is the net magnetic field zero?

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