Two identical positive charges are fixed on the $y$ -axis, at equal distances from the  origin $O$. A particle with a negative charge starts on the $x$ -axis at a large distance  from $O$, moves along the $+ x$ -axis, passes through $O$ and moves far away from $O$. Its acceleration $a$ is taken as positive in the positive $x$ -direction. The particle’s  acceleration a is plotted against its $x$ -coordinate. Which of the following best represents  the plot?

An electron is moving towards $x$-axis. An electric field is along $y$-direction then path of electron is

Four point $+ve$ charges of same magnitude $(Q)$ are placed at four corners of a rigid square frame as shown in figure. The plane of the frame is perpendicular to $Z-$ axis. If a $ -ve$ point charge is placed at a distance $z$ away from centre along axis $(z << L )$ then

A uniform vertical electric field $E$ is established in the space between two large parallel  plates. A small conducting sphere of mass $m$ is suspended in the field from a string of  length $L$. If the sphere is given $a + q$ charge and the lower plate is charged positvely, the period of oscillation of this pendulum is :- 

A particle of mass $\mathrm{m}$ and charge $\mathrm{q}$ is released from rest in a uniform electric field. If there is no other force on the particle, the dependence of its speed $v$ on the distance $x$ travelled by it is correctly given by (graphs are schematic and not drawn to scale)

An electron is projected in the direction of electric field. Just after projection of electron