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Class 10 Class 12

Electric Charges and Fields

How many electrons make up one Coulomb of negative charge?

Using the formula for quantisation of electric charge,
$q = n e, n = q / e$

$\Rightarrow$ $n = \frac{1}{1.6 \times 10^{- 19}} = 6.25 \times 10^{18}$ .

Therefore, $6.25 \times 10^{18}$ electrons make 1 Coulomb of charge.

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Which orientation of an electric dipole in a uniform electric field would correspond to stable equilibrium?

When the direction of the electric dipole moment is aligning in the same direction as that of the Electric field the dipole is said to be in a stable equilibrium.

708 Views

Show that electric field due to line charge at any plane is same in magnitude and directed radially upward.

A thin long straight line L of charge having uniform linear charge density λ is shown by figure. By symmetry, it follows that electric field due to line charge at distance r in any plane is same in magnitude and directed radially upward.

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If the radius of the Gaussian surface enclosing a charge is halved, how does the electric flux through the Gaussian surface change?

According to Gauss's law, Electric flux Φ_E is given by

ϕ_{E} = \oint \vec{E} . \vec{ds} = \frac{Q}{ε_{0}}

where Q is total charge enclosed in the closed surface.
On changing the radius of sphere, the electric flux through the Gaussian surface remains same as the net charge enclosed within the surface is same.

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If electric field in a region is radially outward with magnitude E = Ar. The charge contained in a sphere of radius r_o centred at the origin is

$\frac{4 {πε}_{0} A}{{r_{0}}^{3}}$
$\frac{1}{4 {πε}_{0}} . \frac{A}{{r_{0}}^{3}}$
$4 {πε}_{0} {Ar}_{0}^{3}$
$\frac{1}{4 {πε}_{0}} {Ar}_{0}^{3}$

4 {πε}_{0} {Ar}_{0}^{3}

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Previous Year Papers

Electric Charges and Fields

Show that electric field due to line charge at any plane is same in magnitude and directed radially upward.