Tag: electrostatic potential and capacitance

Questions Related to electrostatic potential and capacitance

A charge $10$ esu is placed at a distance of $2$ cm, from a charge$ 40$ esu and $4$ cm. from another charge -$20$ esu. The potential energy of the charge $10$ esu is :- (In ergs)

potential energy of a system of charges potential energy of various configurations electrostatic potential and capacitance electrostatics physics

  1. $87.5$

  2. $112.5$

  3. $150$

  4. $zero$

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Correct Option: A

Calculate the electrostatic potential energy of two electrons separated bt 3 $\overset { \circ  }{ A } $ in vacuum

potential energy of a system of charges potential energy of various configurations electrostatic potential and capacitance electrostatics physics

  1. $7.69\times10^{-19} J$

  2. $8.69\times10^{-19} J$

  3. $5.69\times10^{-19} J$

  4. $6.69\times10^{-19} J$

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Correct Option: B

A proton and a deuteron are initialy at rest an dare accelerated through the same potential difference. Which following is false concerning  the final properties of the two particles?

potential energy of a system of charges potential energy of various configurations electrostatic potential and capacitance electrostatics physics

  1. They have different speeds

  2. They have same momentum

  3. They have same kinetic energy

  4. They have been subjected to same force

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Correct Option: C

A flat circular fixed disc has a charge +Q uniformly distributed on the disc. A charge +q is thrown with kinetic energy K,towards the disc along its axis The charge is q

potential energy of a system of charges potential energy of various configurations electrostatic potential and capacitance electrostatics physics

  1. will not hit the disc at the center

  2. may return back along its path after touching the disc

  3. may return back along its path without touching the disc

  4. any of the above three situation is possible depending on the magnitude of K

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Correct Option: A

Particle A having positive charge is moving directly head on towards initially stationary positively charged particle B. At the instant when A and B are closest together. 

potential energy of a system of charges potential energy of various configurations electrostatic potential and capacitance electrostatics physics

  1. the momenta of A and B must be equal

  2. the velocities of A and B must be equal

  3. B would have gained less kinetic energy than A would have lost

  4. B would have gained the same momentum as A would have lost

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Correct Option: C,D

Eight charges (each $q$) are placed at the vertices of a regular cube of side $a$. The electric potential energy of the configuration will be $ U=12\times \dfrac { 1 }{ 4\pi \varepsilon _{ 0 } } ,\dfrac { q^{ 2 } }{ a } \times \quad x $ then x.

potential energy of a system of charges potential energy of various configurations electrostatic potential and capacitance electrostatics physics

  1. $ 1+\dfrac { 1 }{ \sqrt { 2 } } +\dfrac { 1 }{ \sqrt { 3 } } $

  2. $ 1+\dfrac { 2 }{ \sqrt { 2 } } +\dfrac { 1 }{ \sqrt { 3 } } $

  3. $ 1+\dfrac { 2 }{ \sqrt { 2 } } +\dfrac { 2 }{ \sqrt { 3 } } $

  4. $ \left[ 1+\dfrac { 1 }{ \sqrt { 2 } } +\dfrac { 1 }{ 3\sqrt { 3 } } \right] $

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Correct Option: D

Two point charges of +10 $\mu c$ and -10 $\mu c$ are placed at a distance $40$ cm in air. Potential energy of the system will be-

potential energy of a system of charges potential energy of various configurations electrostatic potential and capacitance electrostatics physics

  1. $2.25 J$

  2. $2.35 J$

  3. $-2.25 J$

  4. $-2.35 J$

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Correct Option: C

A solid non-conducting sphere of radius $R$ having charge density $\rho = \rho _{0}x$, where $x$ is distance from the centre of sphere. The self potential energy of the sphere is

potential energy of a system of charges potential energy of various configurations electrostatic potential and capacitance electrostatics physics

  1. $\dfrac {\pi \rho _{0}^{2} R^{4}}{6\epsilon _{0}}$

  2. $\dfrac {\pi \rho _{0}^{2} R^{6}}{4\epsilon _{0}}$

  3. $\dfrac {\pi \rho _{0}^{2} R^{6}}{6\epsilon _{0}}$

  4. None of these

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Correct Option: C

If a proton and an electron are accelerated through the same potential difference:

potential energy of a system of charges potential energy of various configurations electrostatic potential and capacitance electrostatics physics

  1. both the proton and electron have same K.E

  2. both the proton and electron have same momentum

  3. both the proton and electron have same velocity

  4. both the proton and electron have same temperature

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Correct Option: A
Explanation:

P.D = V
K.E = eV
Velocity will be equal and opposite

What is the change in potential energy of a particle of charge +q that is brought from a distance of 3r to a distance of 2r by a particle of charge q? 

potential energy of a system of charges potential energy of various configurations electrostatic potential and capacitance electrostatics physics

  1. $kq^2/r$

  2. $-kq^2/6r$

  3. $kq^2/r^2$

  4. $-kq^2//4r^2$

  5. $8kq^2/r^2$

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Correct Option: B
Explanation:

As the $+q$ is brought near by charge $q$ so there is an attraction force it means q is a negative charge, equal to $-q$.
 The electric potential energy of a system of two point charges (  $+q$ ,  $-q$) sepatrated by a distance $3r$ is given by ,
                  $U=k\dfrac{q\times -q}{3r}$  , 
when the separation is reduced to $2r$ then potential energy will become ,
                 $U'=k\dfrac{q\times- q}{2r}$ 
therefore change in potential energy is 
                             $\Delta U=U'-U$ 
or                         $\Delta U=-k\dfrac{q\times q}{2r}+k\dfrac{q\times q}{3r}$
or                         $\Delta U=kq^{2}\left(1/3r-1/2r\right)=-kq^{2}/6r$