Question

In an experiment to find the focal length of a concave mirror a graph is drawn between the magnitudcs of $u$ and $v$. The graph looks like

• A. straight line along the x-direction
• B. a circle in the xz-plane
• C. a circle in the yz-plane
• D. a circle in the xy-plane

Answer 1

Answer: (B)

a circle in the xz-plane

Answer 2

If a particle carrying a positive charge $q$ and moving with velocity $v$ through a point in magnetic field experiences a deflecting force $F$, then magnetic field $B$ is given by $F=qv \times B$ Here $v=v_x= \widehat {i}$ and $B=B_y \widehat {j}$ $B=B_y \widehat {j}$ $\therefore F=ev_xB_y(\widehat {i}\times \widehat {j})=ev_xB_yk$ Hence, subsequent motion of the charged particle will be a circle in the xz-plane.