An electron enters an electric field with its velocity in the direction of the electric lines of force. Then 

(1) The path of the electron will be a circle

(2) The path of the electron will be a parabola

(3) The velocity of the electron will decrease

(4) The velocity of the electron will increase

The dimension of (1/2) ${\epsilon }_0{E}^2<mspace\; width="1em"></mspace><mspace\; width="1em"></mspace>({\epsilon }_0$: permittivity of free space; E: electric field) is

(1) MLT^–1

(2) ML²L^–2

(3) ML^–1T^–2

(4) ML²T^–1

An electron having charge ‘e’ and mass ‘m’ is moving in a uniform electric field E. Its acceleration will be 

(1) $\frac{e^2}{m}$

(2) $\frac{E^{2}e}{m}$

(3) $\frac{eE}{m}$

(4) $\frac{mE}{e}$

A pendulum bob of mass $30.7\times {10}^{-6}kg$ and carrying a charge $2\times {10}^{-8}C$ is at rest in a horizontal uniform electric field of 20000 V/m. The tension in the thread of the pendulum is $(g=9.8m/s^2)$

(1) $3\times {10}^{-4}N$

(2) $4\times {10}^{-4}N$

(3) $5\times {10}^{-4}N$

(4) $6\times {10}^{-4}N$ 

A charged ball B hangs from a silk thread S, which makes an angle θ with a large charged conducting sheet P, as shown in the figure. The surface charge density σ of the sheet is proportional to 

(1) sin θ

(2) tan θ

(3) cos θ

(4) cot θ

Two infinitely long parallel conducting plates having surface charge densities +σ and –σ respectively, are separated by a small distance. The medium between the plates is a vacuum. If ε₀ is the dielectric permittivity of vacuum, then the electric field in the region between the plates is 

(1)  $0<mspace\; width="1em"></mspace>volts/meter$

(2) $\frac{\sigma }{2{\epsilon }_o}volts/meter$

(3) $\frac{\sigma }{{\epsilon }_o}volts/meter$

(4) $\frac{2\sigma }{{\epsilon }_o}volts/meter$ 

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

(1) – ve charge oscillates along the Z-axis.

(2) It moves away from the frame

(3) It moves slowly towards the frame and stays in the plane of the frame

(4) It passes through the frame only once.

A cylinder of radius R and length L is placed in a uniform electric field E parallel to the cylinder axis. The total flux for the surface of the cylinder is given by 

(1) $2\pi R^{2}E$

(2) $\pi R^2/E$

(3) $(\pi R^2-\pi R)/E$ 

(4) Zero

An electric charge q is placed at the centre of a cube of side α. The electric flux on one of its faces will be 

(1) $\frac{q}{6{\epsilon }_0}$

(2) $\frac{q}{{\epsilon }_0{a}^2}$

(3) $\frac{q}{4\pi {\epsilon }_0{a}^2}$

(4) $\frac{q}{{\epsilon }_0}$ 

Total electric flux coming out of a unit positive charge put in air is 

(1) ${\epsilon }_0$

(2) ${\epsilon }_0^{-1}$

(3) ${\left(4p{\epsilon }_0\right)}^{-1}$

(4) $4\pi {\epsilon }_0$