Question

For a positive charged particle moving in xy-plane initially along the X-axis. There is a sudden change in its path due to the presence of electric and/or magnetic fields beyond P. The curved path is shown in then-plane and is found to be non-circular. Which one of the following combinations is possible?

• A. $E=0;B=b\hat{i}-c\hat{k}$
• B. $E=b\hat{i};B=c\hat{k}+a\hat{i}$
• C. $E=0;B=c\hat{j}+b\hat{k}$
• D. $E=a\hat{i};B=c\hat{i}+b\hat{j}$

Answer 1

Answer: (B)

$E=b\hat{i};B=c\hat{k}+a\hat{i}$

As the curved path is confined to the $XY$ plane the component of magnetic field effective deflecting the particle is the $Z$component only. The other component should be the $X$-component since the $X$-component cannot deflect the charged particle proceeding along the $X$-direction. There has to be an electric field since the path of the particle is non-circular. All these conditions are satisfied by option $\left(b\right)$, so the correct option is $\left(b\right)$.