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71.

If the electric fluxes entering and leaving an enclosed surface respectively are Φ_{1} and Φ_{2,} the electric charge inside the surface will be

(Φ

_{2}− Φ_{1}) ε_{0}(Φ

_{1}+ Φ_{2}) / ε_{0}(Φ

_{2}− Φ_{1}) / ε_{0}(Φ

_{1}+ Φ_{2}) / ε_{0}

72.

Shown below is a distribution of charges. The flux of electric field due to these charges through the surface is

$\frac{3\mathrm{q}}{{\mathrm{\epsilon}}_{0}}$

zero

$\frac{2\mathrm{q}}{{\mathrm{\epsilon}}_{0}}$

$\frac{\mathrm{q}}{{\mathrm{\epsilon}}_{0}}$

73.

Two point charges + q and + 4q are located at x = O and x = L respectively. The location of a point on the x-axis at which the net electric field due to these two points charges is zero, is

L / 3

2 L

4 L

8 L

74.

If electric flux entering and leaving an enclosed surface is ${\mathrm{\varphi}}_{1}$ and ${\mathrm{\varphi}}_{2}$ respectively, the electric charge inside the enclosed surface will be

$\left({\mathrm{\varphi}}_{1}+{\mathrm{\varphi}}_{2}\right){\mathrm{\epsilon}}_{0}$

$\left({\mathrm{\varphi}}_{2}-{\mathrm{\varphi}}_{1}\right){\mathrm{\epsilon}}_{0}$

$\left({\mathrm{\varphi}}_{1}+{\mathrm{\varphi}}_{2}\right)/{\mathrm{\epsilon}}_{0}$

$\left({\mathrm{\varphi}}_{2}-{\mathrm{\varphi}}_{1}\right)/{\mathrm{\epsilon}}_{0}$

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75.

The electric field in a region is given by E = $\left(4\stackrel{\wedge}{\mathrm{i}}+3\stackrel{\wedge}{\mathrm{j}}\right)$V/m. The net flux passing through a square area of side 4 m parallel to y-z plane is

32 V-m

16 V-m

12 V-m

64 V-m

76.

Two concentric conducting spherical shells A and B having radii r_{A} and r_{B} (r_{B} > rA) are charged to Q_{A} and -Q_{B} $\left(\left|{\mathrm{Q}}_{\mathrm{B}}\right|\left|{\mathrm{Q}}_{\mathrm{A}}\right|\right)$ . The electric field along a line passing through the centre is

$\left|{\mathrm{Q}}_{\mathrm{B}}\right|\left|{\mathrm{Q}}_{\mathrm{A}}\right|$

77.

Two charged spheres separated by a distance d exert some force (F) on each other. If they are immersed in a liquid of dielectric constant 4, then what is the force exerted, if all other conditions are same ?

2F

4F

$\frac{\mathrm{F}}{2}$

$\frac{\mathrm{F}}{4}$

78.

A charge q is located at the centre of a cube. The electric flux through any face is

$\frac{4\mathrm{\pi q}}{6\left(4{\mathrm{\pi \epsilon}}_{0}\right)}$

$\frac{\mathrm{\pi q}}{6\left(4{\mathrm{\pi \epsilon}}_{0}\right)}$

$\frac{\mathrm{q}}{6\left(4{\mathrm{\pi \epsilon}}_{0}\right)}$

$\frac{2\mathrm{\pi q}}{6\left(4{\mathrm{\pi \epsilon}}_{0}\right)}$

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79.

An electron enters uniform electric field maintained by parallel plates and of value E Vm^{-1} with a velocity v ms^{-1} , the plates are separated by a distance d metre, then acceleration of the electron in the field is

$\frac{\mathrm{Ee}}{\mathrm{m}}$

$\frac{-\mathrm{Ee}}{\mathrm{m}}$

$\frac{\mathrm{Ed}}{\mathrm{m}}$

$\mathrm{Ee}\frac{\mathrm{d}}{\mathrm{m}}$

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The electrostatic field due to a charged conductor just outside the conductor is

zero and parallel to the surface at every point inside the conductor

zero and is normal to the surface at every point inside the conductor

parallel to the surface at every point and zero inside the conductor

normal to the surface at every point and zero inside the conductor

D.

normal to the surface at every point and zero inside the conductor

The electrostatic field due to a charged conductor just outside the conductor is normal to the surface at every point and zero inside the conductor.

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