A wire of length 6cm makes an angle of 20° with a 3 mT magnetic field. What current is needed to cause an
upward force of 1.5 x 10-4 N?

Approximately (approximately ) assuming that the magnetic field and the wire are both horizontal.

Explanation:

Let denote the angle between the wire and the magnetic field.

Let denote the magnitude of the magnetic field.

Let denote the length of the wire.

Let denote the current in this wire.

The magnetic force on the wire would be:

.

Because of the term, the magnetic force on the wire is maximized when the wire is perpendicular to the magnetic field (such that the angle between them is .)

In this question:

Rearrange the equation to find an expression for , the current in this wire.

.

think its the third option

it doesn't. it was imagined up in the middle ages.