When you bring a current-carrying wire down onto the top of a compass, aligned w

Question

When you bring a current-carrying wire down onto the top of a compass, aligned with the original direction of the needle and 3 mm above the needle, the needle deflects by = 15 degrees (see the figure).

(a) Which of the following statements are correct? Select all that apply.

- Conventional current in the wire is flowing downward (South).

- The magnetic field under the wire, due to the current, points to the East.

- The magnetic field under the wire, due to the current, points to the West.

- Conventional current in the wire flows upward (North).

- Electron current in the wire is flowing upward (North).

- The magnetic field under the wire, due to the current, points North.

(b) Calculate the amount of conventional current flowing in the wire. The measurement was made at a location where the horizontal component of the Earth's magnetic field is BEarth 2 10-5 tesla.

____________ A

Explanation / Answer

a)The following statements are correct :

- Conventional current in the wire is flowing downward (South).

- The magnetic field under the wire, due to the current, points to the East.

- Electron current in the wire is flowing upward (North).

b) We have, B = (u0.I)/(2pi.R)

So, I = (2pi.R.B)/(u0) = (2pi.(0.003)(2 10-5)) / (4pi x 10^-7) = 0.3A

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