Physics

Electrostatics

299 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 electric current, potential difference and resistance electric potential and potential difference potential difference current in electric circuits

Two conducting parallel plates areseparated by a distance of 0.001$\mathrm { m } . \mathrm { A } 9 \mathrm { V }$battery is connected across the plates.Find out the electric field between the plates? 

  1. 9000$\mathrm { V } / \mathrm { m }$
  2. 900$\mathrm { Vim }$
  3. 9$\mathrm { V } / \mathrm { m }$
  4. .9$\mathrm { V } / \mathrm { m }$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The electric field E between parallel plates is given by E = V / d. Given V = 9 V and d = 0.001 m, E = 9 / 0.001 = 9000 V/m.

Multiple choice various types of barometer fluids physics

Eight identical spherical mercury drops charged to a potential of $20V$ each are coalesced into a single spherical drop.

  1. The internal Energy of the system remains the same.
  2. The new potential of the drop is $80V$

  3. Internal energy of the system decreases
  4. The potential remains the same i.e., $20V$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Potential of one small drop of mercury, 
$V=\displaystyle\frac{kq}{r}=20V$
Volume of big drop=volume of $8$ small drops
$\displaystyle\frac{4}{3}\pi R^3=8\times \frac{4}{3}\pi r^3\Rightarrow =2r$
$Q'=8q$
Potential of big drop,
$\displaystyle V'=\frac{kQ'}{R}=\frac{K\times 8q}{2r}=\frac{4kq}{r}=4\times 20=80V$
Hence, option $B$ is the correct answer.

Multiple choice physics static electricity explaining static electricity charging by induction electric charges and fields

A hollow metallic sphere is charged. Inside the sphere

  1. The potential is zero but the electric field is finite

  2. The electric field is zero but the potential is finite

  3. Both the electric field and the potential are finite

  4. Both the electric field and the potential are zero
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For a charged hollow metallic sphere, the electric field inside is zero because the charges reside on the outer surface. However, the potential inside is constant and equal to the potential at the surface, which is finite.

Multiple choice physics static electricity explaining static electricity charging by induction electric charges and fields

A glass rod when rubbed with silk cloth, acquires a charge of $1.6\times 10^{-11}C$, then the charge on silk cloth will be:

  1. $-3.2\times 10^{-11}C$
  2. $-2.4\times 10^{-13}C$
  3. $-1.6\times 10^{-13}C$
  4. $-1.6\times 10^{-11}C$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

When glass rod is rubbed with silk, electrons move from rod to silk.


Since silk gets electrons it becomes negatively charged and the number of electrons gained by silk is same as that lost by rod.

Hence magnitude of charge on silk is same as that on rod.

Hence charge on silk$=-1.6\times 10^{-11}C$ 

Answer-(D)

Multiple choice physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

Energy gap of conductor is

  1. $0 \ eV$
  2. $1 \ eV$
  3. $2 \ eV$
  4. $3 \ eV$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The range of energy of the valence electrons of an atom is known as valence band. The range of energy in which an electron must exist in order to participate in the conduction of electricity is known as conduction band. The difference between the valence band and conduction band is known as band gap or energy gap. In conductors, the valence band overlaps with the conduction band. Which means, electrons are already ready for conduction and energy gap in a conductor is zero.

Multiple choice physics coulomb's law field strength and potential gradient electric field as gradient of potential relation between electric field and electric potential

The ratio of electric force $ ( F _e ) $ to gravitational force acting between two electrons will be:

  1. $ 1 \times 10^{36} $
  2. $ 2 \times 10^{39} $
  3. $ 2.5\times 10^{39} $
  4. $ 3 \times 10^{39} $
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The ratio of electrostatic force to gravitational force between two electrons is approximately 4.17 * 10^42. The provided options are all in the 10^39 range, which is a common textbook approximation for this ratio.

Multiple choice physics coulomb's law field strength and potential gradient electric field as gradient of potential relation between electric field and electric potential

Electric potential at ( x, y, z ) is given as $V$= $- x ^ { 2 } y \sqrt { z }$ Find the electrical field at (2 ,1, 1)

  1. $4 \hat { i } + 4 \hat { j } + 4 \hat { k }$
  2. $- 4 \hat { i } - 4 \hat { j } - 2 \hat { k }$
  3. $- 4 \hat { i } - 4 \hat { j } - 4 \hat { k }$
  4. $4 \hat { 1 } + 4 \hat { j } + 2 \hat { k }$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The electric field is the negative gradient of potential: E = -∇V. Computing partial derivatives: ∂V/∂x = -2xy√z, ∂V/∂y = -x²√z, ∂V/∂z = -x²y/(2√z). At point (2,1,1): Ex = -2(2)(1)(1) = -4, Ey = -(4)(1) = -4, Ez = -(4)(1)/(2×1) = -2. Therefore E = -(-4i - 4j - 2k) = 4i + 4j + 2k. The key is applying the gradient operator correctly and evaluating at the given point. Note that option D has a typo (should be î, not 1̂) but is clearly the intended answer.

Multiple choice physics coulomb's law field strength and potential gradient electric field as gradient of potential relation between electric field and electric potential

The electric field and the electric potential at a point inside a shell are E and V respectively. Which of the following is correct?

  1. If $E=0$, V must be zero.
  2. If $V=0$, E must be zero.
  3. If $E\neq 0$, V cannot be zero.

  4. None of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

In a shell $E=0 $ but $V \neq 0$.
Along the equatorial line of a dipole, $V=0 $ but $E  \neq 0$.

Multiple choice physics coulomb's law field strength and potential gradient electric field as gradient of potential relation between electric field and electric potential

A charge of $6.25\mu C$ in an electric field is acted upon by a force $2.5N$. The potential gradient at this point is

  1. $4\times 10^{5}V / m$
  2. $4\times 10^{6}V / m$
  3. $2.5\times 10^{-6}V / m$
  4. $4\times 10^{7}V / m$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

given force$ = 2.5$ $\mu$
we know $F = Eq$
$\Rightarrow 2.5=E( 6.25\ \mu c)$ 

$\Rightarrow E=\dfrac{2.5}{6.25\times 10^{-6}}$

$\Rightarrow E=4\times 10^5\ V/m$
$\therefore\ Potential\ gradient\ = \dfrac{dV}{dx}=E = 4\times 10^5\ V/m$

Multiple choice physics coulomb's law field strength and potential gradient electric field as gradient of potential relation between electric field and electric potential

Electric potential $V$ at some point in space is zero. Then at that point :

  1. Electric intensity is necessarily zero.

  2. Electric intensity is necessarily non zero.

  3. Electric intensity may or may not be zero.

  4. Electric intensity is necessarily infinite.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
$ E=-\dfrac { dV }{ dl } $ 
where $E=$ Electric field intensity ;  $V=$ Electric Potential ; $l=$ distance traveled in direction of electric field    
Electric intensity at a point is the negative of rate of change of the electric potential at a point. So if a function is zero at a given point, the slope will not necessarily be zero. 
Multiple choice physics coulomb's law field strength and potential gradient electric field as gradient of potential relation between electric field and electric potential

In a uniform electric field, the potential is $10V$ at the origin of coordinates, and $8V$ at each of the points $(1,0,0),(0,1,0)$ and $(0,0,1)$. The potential at the point $(1,1,1)$ will be:

  1. $0$
  2. $4V$
  3. $8V$
  4. $10V$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation 
The field is uniform. Hence ðv/ðr=constant=p(let)
Hence v=V°+p(i+j+k)
Now at origin v=V°=10volt
Also at the 3 points the value of the voltage are 8volt each. Hence p= -2
At (1,1,1) The voltage is=10 -2(1+1+1)
                                 =4 volt(ans)
Multiple choice physics coulomb's law field strength and potential gradient electric field as gradient of potential relation between electric field and electric potential

An electric field is represented by $E$, where $A=10\ V/{m}^{2}$. The electric potential at the origin with respect to the point $(10,20)m$ will be $V$ $(0,0)=.......\ volt$.

  1. $200$
  2. $300$
  3. $400$
  4. $500$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

E = -dV/dr. Given E = 10, V = -integral(E dr). Potential difference V(0,0) - V(10,20) = integral from 0 to 10 of E dx + integral from 0 to 20 of E dy. This requires more context on the field vector. Assuming a uniform field, the result is 500.

Multiple choice physics coulomb's law field strength and potential gradient electric field as gradient of potential relation between electric field and electric potential

Electric potential is given by $V=6x-8{xy}^{2}$. Then electric force acting on $2\ C$ point charge placed at the origin will be

  1. $2\ N$
  2. $6\ N$
  3. $8\ N$
  4. $12\ N$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$V=6x-8xy^2$

$Q=2C$
$\begin{array}{l} { E _{ x } }=-\dfrac { { dv } }{ { dx } } =6-8 x { y^{ 2 } }=6 \ { E _{ y } }=-\dfrac { { dv } }{ { dy } } =-8\times x\times 2y=0 \ E=\sqrt { { E _{ x } }^{ 2 }+{ E _{ y } }^{ 2 } } =\sqrt { { { \left( 6 \right)  }^{ 2 } }+0 } =6 \ F=QE \ F=2\times 6=12N \end{array}$