A wire is strung horizontally through a space filled with a uniform magnetic fie

Question

A wire is strung horizontally through a space filled with a uniform magnetic field. The field lines emerge out of the page (see diagram).

a) If a switch is thrown and current flows from left to right in the wire, is there a force on the wire? If so, in what direction is that force?

b) If the magnetic field strength is 0.5 T, the length of the wire in the region with field is 0.1 m, and the current is 0.05 A, what is the magnitude of the force?

c) The wire is strung through the magnetic field differently, at right angles to its previous arrangement, so now the wire runs into the page. When a current is switched on flowing into the page (anti-parallel to the field lines), is there a force on the wire? If so, in what direction is that force?

Explanation / Answer

i = left

-i = right

j = up

-j = down

k = out

-k into

a)

F = I*(LxB) = I*L*B*sintheta

here L along horizantal (i)

B is out of the page (k)

the angle theta = 90

F will act

the direction = i x k = -j (down wards)

b)

F = 0.05*0.1*0.5 = 0.0025 N

(c)

now L is along -k

angle = 180

F = I*L*B*sin180 = 0

NO force

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