question_answer

A conducting loop carrying a current I is placed in a uniform magnetic field pointing into the plane of the paper as shown. The loop will have a tendency to    [IIT-JEE (Screening) 2003]

A)            Contract                                 

B)            Expand

C)            Move towards +ve x -axis

D)            Move towards ?ve x-axis

Correct Answer: B

Solution :

                   Net force on a current carrying loop in uniform magnetic field is zero. Hence the loop can?t translate. So, options (c) and (d) are wrong. From Fleming's left hand rule we can see that if magnetic field is perpendicular to paper inwards and current in the loop is clockwise (as shown) the magnetic force \[\overrightarrow{{{F}_{m}}}\] on each element of the loop is radially outwards, or the loops will have a tendency to expand.