A square loop of wire lies in the plane of the page and carries a current I as shown.There is a uniform magnetic field directed towards the top of the page, as indicated.The loop will tend to rotate:
A)about PQ with KL coming out of the page
B)about PQ with KL going into the page
C)about RS with MK coming out of the page
D)about RS with MK going into the page
E)about an axis perpendicular to the page

Question

A square loop of wire lies in the plane of the page and carries a current I as shown.There is a uniform magnetic field  directed towards the top of the page, as indicated.The loop will tend to rotate: 
A)about PQ with KL coming out of the page 
B)about PQ with KL going into the page 
C)about RS with MK coming out of the page 
D)about RS with MK going into the page 
E)about an axis perpendicular to the page

Quizplus · Accepted Answer

According to Fleming's left-hand rule, the direction of the force on the sides of the loop is given by the direction of the magnetic field (top of the page) crossed with the direction of the current in the wire (clockwise when viewed from above). This results in a counterclockwise torque on the loop about PQ, with KL coming out of the page. Therefore, the loop will tend to rotate about PQ with KL coming out of the page.

A Square Loop of Wire Lies in the Plane of the Page