Question

If instead of changing the direction of magnetic field the direction of battery is reversed, what effect will you note?

• A. The wire can be moved backward or forward by changing the direction of battery.
• B. The wire will continue to move in the same direction.
• C. The magnetic field will reverse.
• D. None of these.

Answer 1

The correct option is A The wire can be moved backward or forward by changing the direction of battery.

${\overrightarrow{F}}_{mag}=i\int (\overrightarrow{dl}\times \overrightarrow{B})$
The direction of ${\overrightarrow{F}}_{mag}$ will change if direction of $\overrightarrow{B}$ is reversed or direction of current is changed/reversed$($ direction of $\overrightarrow{dl}$ changes when current direction is changed$)$.
Hence, the wire can be moved forward or backward by changing the polarity of the battery.
Magnetic field is external, hence will not change. The induced emf will have a current flow and creates a magnetic field which will oppose the external magnetic field, but is not considered here.