Physics

Electrostatics

303 Questions

Electrostatics deals with electric charges, fields, and potentials at rest. It is a crucial topic for physics sections in engineering and civil services competitive examinations. Review these questions to build a strong understanding of Coulomb law, electric dipoles, Gauss law, and electric flux.

Electric field and potentialElectric dipole momentGauss Law applicationsCoulomb force calculationsCharge distribution on spheresEquipotential surfaces

Electrostatics Questions

Multiple choice physics upthrust in fluids, archimedes' principle and floatation density of a fluid density of fluid density and relative density

Two infinite linear charges are placed parallel to each other at a distance 0.1 m from each other. if the linear charge density on each is 5 $ 5 \mu \ C /m $ , then the force acting on a unit length of each linear charge will be

  1. 2.5 N/m

  2. 3.25 N/m

  3. 4.5 N/m

  4. 7.5 N/m
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The force per unit length between two infinite parallel wires is F/L = (mu_0 * lambda_1 * lambda_2) / (2 * pi * d). Using mu_0 = 4 * pi * 10^-7, lambda = 5 * 10^-6 C/m, and d = 0.1 m, the calculation yields 4.5 N/m.

Multiple choice physics measurements and units measurement of area and volume measurement of volume measurement of area, volume and density

Four  positive charges $ ( 2 \sqrt 2-1 )Q $ are arranged at corner of square . another charge q is placed at the centre of the square. resultant force acting on each corner is zero if q is :

  1. $-7Q/4$
  2. $-4Q/ 7$
  3. $-Q$
  4. $none$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

For the resultant force on each corner charge to be zero, the electrostatic force due to the central charge q must balance the repulsive forces from the other three corner charges. Calculating the vector components along the diagonal yields q = -7Q/4.

Multiple choice physics magnetic fields and electromagnetism magnetic flux density magnetic flux electromagnetic induction

A charge q is placed at the centre of a cylinder of radius R and length 2R. Then electric flux through the curved surface of the cylinder is 

  1. $\cfrac { q }{ 2 { \epsilon } _{ 0 } } $
  2. $\cfrac { q }{ 4 { \epsilon } _{ 0 } } $
  3. $\cfrac { q }{ \sqrt { 2 } { \epsilon } _{ 0 } } $
  4. $\cfrac { q }{ 2\sqrt { 2 } { \epsilon } _{ 0 } } $
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice physics magnetic fields and electromagnetism magnetic flux density magnetic flux electromagnetic induction

A sphere of radius $R$ and charge $Q$ is placed inside an imaginary sphere of radius $2R$. Whose center coincides with the given sphere. The flux related to the imaginary sphere is:

  1. $\dfrac {Q}{\in _{0}}$
  2. $\dfrac {Q}{2\in _{0}}$
  3. $\dfrac {4Q}{\in _{0}}$
  4. $\dfrac {2Q}{\in _{0}}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

According to Gauss's Law, the total electric flux through any closed surface is equal to the enclosed charge divided by epsilon_0. Since the inner sphere with charge Q is entirely enclosed by the imaginary sphere, the flux is Q/epsilon_0.

Multiple choice physics magnetic fields and electromagnetism magnetic flux density magnetic flux electromagnetic induction

The electric field in a certain region is $\left( 10\hat { i } +5\hat { j }  \right) \times { 10 }^{ 4 }N/C$. What is the flux due to this field over an area of $\left( 3\hat { i } +3\hat { j }  \right) \times { 10 }^{ -2 }{ m }^{ 2 }$ in ${ Nm }^{ 2 }/C?$

  1. $4.5\times { 10 }^{ 3 }$
  2. $3.5\times { 10 }^{ 3 }$
  3. $2.5\times { 10 }^{ 3 }$
  4. $1.5\times { 10 }^{ 3 }$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Electric flux is the dot product of the electric field vector and the area vector. Phi = (10i + 5j) * 10^4 * (3i + 3j) * 10^-2 = (30 + 15) * 10^2 = 45 * 10^2 = 4.5 * 10^3 Nm^2/C.

Multiple choice physics capacitance capacitors in parallel combination of capacitors capacitors in parallel and series

Two parallel plates have equal and opposite charge. When the space between them is evacuated. the electric field between the plates $2 \times {10^5}\,V/m.$ When the space is filed with dielectric the electric field becomes ${10^5}\,V/m$ The dielectric constant of he dielectric material is 

  1. $2$
  2. $4$
  3. $5$
  4. $9$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Dielectric constant$:-$

$K = \dfrac{{{E _0}}}{E}$
$ = \dfrac{{2 \times {{10}^5}}}{{1 \times {{10}^5}}} = 2$
Hence,
option $(A)$is correct answer

Multiple choice physics magnetic fields and electromagnetism contact and non-contact forces comparing force in magnetic, electric and gravitational fields identifying forces

Four point charge of $+10^{-7}C, -10^{-7}C, -2\times 10^{-7}C$ and $+2\times 10^{-7}C$ are placed respectively at the corners $A, B, C, D$ of a $0.05\ m$ square. Find the magnitude of the resultant force on the charge at $D$.

  1. $0.2\ dyne$
  2. $0.2\ newton$
  3. $2\ dyne$
  4. $0.02\ newton$
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice torque on a dipole in a uniform electric field electric dipole electric charges and fields electrostatics physics

An electric dipole of moment $ \vec { p } $ is placed in a uniform electric field$\vec { E }$ . Then
(i) The torque on the dipole is $\vec { p } \times \vec { E } $.
(ii) The potential energy of the system is $\vec { p } \cdot \vec { E } $.
(iii) The resultant force on the dipole is zero.
Choose the correct option.

  1. (i), (ii) and (iii) are correct

  2. (i) and (iii) are correct and (ii) is wrong

  3. Only (i) is wrong

  4. (i) and (ii) are correct and (iii) is wrong
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In a uniform electric field, $\vec { E } $, dipole experiences a torque $\vec { \tau  } $ given by $\vec { \tau  } =\vec { p } \times \vec { E } $ but experiences no force. The potential energy of the dipole in a uniform electric field $\vec { E } $ is $U=-\vec { p } .\vec { E } $

Multiple choice torque on a dipole in a uniform electric field electric dipole electric charges and fields electrostatics physics

An electric dipole of length 20 cm having $\pm3 \times { 10 }^{ -3 }$ C charge placed at 60 with respect to a uniform electric field experiences a torque of magnitude 6 N m. the potential energy of the dipole is:

  1. -2$\sqrt { 3 }$ J
  2. 5$\sqrt { 3 }$ J
  3. -3$\sqrt { 2 }$ J
  4. 3$\sqrt { 5 }$ J
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Here,

Length of dipole $2a= 20\ cm=0.2\ m$
Charge, $q= \pm 3\times 10^{-3}\ C$,             $\theta=60^o$
Torque, $\tau=6\ Nm$
As, $\tau=pEsin\ \theta$
or $E=\dfrac{\tau}{psin \theta}= \dfrac{\tau}{q(2a)sin \theta}(\because p=q(2a)$

$\therefore E=\dfrac{6}{3\times 10^{-3}\times 20 \times 10^{-2} \times sin\ 60^o}= \dfrac{10^5}{5\sqrt 3} NC^{-1}$

Potential energy of dipole, $U=-pEcos \theta=-q(2a) E cos \theta $

$\implies U= -3\times 10^{-3}(20 \times 10^{-2} )\dfrac{10^5}{5\sqrt 3} cos 60^o= -2\sqrt 3\ J$

Multiple choice torque on a dipole in a uniform electric field electric dipole electric charges and fields electrostatics physics

An electric dipole is kept on the axis of a uniformly charged ring at distance $\frac{R}{\sqrt{2}}$ from the centre of the ring. The direction of the dipole moment is along the axis. The dipole moment is P, charge of the ring is Q & radius of the ring is R. The force on the dipole is ___________________.

  1. (a) $\frac{4 k P Q}{3\sqrt{3} R^{2}}$
  2. (b) $\frac{4 k P Q}{3\sqrt{3} R^{3}}$
  3. (c) $\frac{2 k P Q}{3\sqrt{3} R^{2}}$

  4. (d) zero
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The electric field on the axis of a ring is E = kQx / (R^2 + x^2)^(3/2). For a dipole at x = R/sqrt(2), the field gradient exerts a force F = p * (dE/dx). Calculating the derivative and substituting gives the force.