Electrostatics Overview
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Questions and Answers

What determines the extent of polarization in a dielectric material?

  • The type of external field applied
  • The temperature of the dielectric material only
  • The relative strength of dipole potential energy and thermal energy (correct)
  • The size of the dielectric slab
  • What is the term used to describe the dipole moment per unit volume in a dielectric?

  • Dielectric constant
  • Susceptibility
  • Polarization (correct)
  • Temperature coefficient
  • In the equation P = ε0 χe E, what does χe represent?

  • Total charge density
  • Electric susceptibility of the dielectric medium (correct)
  • Molecular dipole strength
  • Electric field strength
  • What happens to the positive and negative charges in a dielectric when it is subjected to an external field?

    <p>The positive ends of the dipoles remain unneutralized at one surface</p> Signup and view all the answers

    What factor tends to disrupt the alignment of dipoles in a dielectric material?

    <p>Thermal energy</p> Signup and view all the answers

    What is the result of applying a uniform external field to a dielectric slab?

    <p>Uniform polarization of the dielectric</p> Signup and view all the answers

    Which statement is true regarding the internal field of a polarized dielectric?

    <p>It has no net charge but has a net dipole moment</p> Signup and view all the answers

    What occurs at the surfaces of a dielectric when it is polarized in an external electric field?

    <p>A net charge density forms due to unneutralized dipole charges</p> Signup and view all the answers

    What happens to the work done by an external force when moving charge q from point R to point P?

    <p>It is negative of the work done by electric force.</p> Signup and view all the answers

    What does the potential energy difference $ riangle U$ represent?

    <p>The work done by the external force moving from R to P.</p> Signup and view all the answers

    When the external force is removed after reaching point P, what does the electric force do?

    <p>It causes the charge q to accelerate towards point R.</p> Signup and view all the answers

    Which of the following statements is true regarding the direction of work done by the electric field?

    <p>It is in the opposite direction to the motion of the charge.</p> Signup and view all the answers

    How does the potential energy at point P relate to the work done moving charge q from R to P?

    <p>It is equal to the work done.</p> Signup and view all the answers

    What influences the value of the potential energy difference $ riangle U$?

    <p>Only the initial and final positions of the charge.</p> Signup and view all the answers

    Why is the work done by electric force considered negative in this context?

    <p>Because it opposes the movement of charge q.</p> Signup and view all the answers

    If charge q is moved with constant speed, what can be said about the net force acting on it during the process?

    <p>It is equal to the electric force.</p> Signup and view all the answers

    What is the total dipole moment of all the molecules in the substance when the dipole moment of each molecule is $10^{-29}$ C m?

    <p>$6 × 10^{-6}$ C m</p> Signup and view all the answers

    What is the initial potential energy (Ui) when $q = 0°$?

    <p>$-6$ J</p> Signup and view all the answers

    What is the formula for the electrostatic potential V at a distance r from a point charge Q?

    <p>$\frac{Q}{4\pi\epsilon_0 r}$</p> Signup and view all the answers

    For a negative charge Q, how does the work done by the external force compare when a positive test charge is brought from infinity to a point P?

    <p>The work done is negative.</p> Signup and view all the answers

    What does the change in potential energy indicate when dipoles align with a new electric field direction?

    <p>Energy is released as heat.</p> Signup and view all the answers

    What happens to the electrostatic field inside a conductor?

    <p>It is zero.</p> Signup and view all the answers

    What does it imply if the electrostatic potential V is negative when Q < 0?

    <p>It implies that work done by the electrostatic force is negative.</p> Signup and view all the answers

    In metallic conductors, which charged particles are primarily responsible for conducting electricity?

    <p>Valence electrons</p> Signup and view all the answers

    How does the electrostatic potential vary with distance r from a point charge?

    <p>It varies as $1/r$.</p> Signup and view all the answers

    What is the final potential energy (Uf) when the dipoles align at an angle of $60°$?

    <p>$-3$ J</p> Signup and view all the answers

    What happens to the work done in bringing a charge from infinity to point P if the charge Q is doubled?

    <p>It doubles.</p> Signup and view all the answers

    Which of the following correctly describes the relationship between electrostatic force and displacement when bringing a positive charge to a point P near a negative charge?

    <p>Both are in the same direction.</p> Signup and view all the answers

    In the context of electrolytic conductors, what adds complexity to the movement of charge carriers?

    <p>Chemical forces</p> Signup and view all the answers

    When switching the direction of an external electric field by 60º, what is the energy released during the alignment of dipoles?

    <p>$3$ J</p> Signup and view all the answers

    What is the implication of considering the potential at infinity to be zero?

    <p>It simplifies calculations for potential energy.</p> Signup and view all the answers

    When integrating to find the potential due to a point charge, which variable is used in the limits of integration?

    <p>The distance from the charge to the point of interest.</p> Signup and view all the answers

    What does the electrostatic potential (V) at a point represent?

    <p>The work done in bringing a unit positive charge from infinity to that point.</p> Signup and view all the answers

    When calculating the work done per unit test charge, which quantity is used as an infinitesimal change?

    <p>The work done, dW.</p> Signup and view all the answers

    How does the work done by an external force depend on the electrostatic field?

    <p>It depends only on the initial and final positions.</p> Signup and view all the answers

    What is assumed about the charge Q when determining the potential at point P?

    <p>It is taken to be positive for definiteness.</p> Signup and view all the answers

    What does the work done in bringing a unit positive test charge from infinity indicate about the electrostatic potential?

    <p>The work done is independent of the test charge's mass.</p> Signup and view all the answers

    What is the significance of choosing the potential to be zero at infinity?

    <p>It provides a baseline reference for potential at all other points.</p> Signup and view all the answers

    Why is it important to consider the electrostatic force acting on a test charge when determining potential?

    <p>It allows for an equal external force to be applied.</p> Signup and view all the answers

    What is implied about the potential difference in regions with electrostatic fields?

    <p>It depends on the charge configuration and distance.</p> Signup and view all the answers

    Study Notes

    Work done by external forces

    • Work done by external forces in moving a charge q from R to P is equal to the negative of the work done by the electric force.
    • This work done is stored as potential energy.
    • Potential energy difference between two points is defined as the work required to be done by an external force in moving charge q from one point to another.

    Electrostatic potential

    • Electrostatic potential (V) at any point in a region with electrostatic field is the work done in bringing a unit positive charge from infinity to that point.
    • The potential at infinity is zero.

    Potential due to a point charge

    • The potential at point P due to a charge Q at the origin is given by: V(r) = Q/(4πε₀r).
    • The potential is positive for a positive charge Q and negative for a negative charge Q.
    • The variation of potential V with r is proportional to 1/r.

    Electrostatics of conductors

    • Conductors contain mobile charge carriers. In metallic conductors, these charge carriers are electrons.
    • Inside a conductor, electrostatic field is zero.
    • The free electrons in a conductor move randomly in different directions.
    • In an external electric field, the electrons drift against the direction of the field.

    Dielectrics

    • The extent of polarisation of a dielectric depends on the dipole potential energy in the external field and thermal energy.
    • The dipole moment per unit volume is called polarisation and is denoted by P.
    • For linear isotropic dielectrics, P = ε₀ χe E, where χe is the electric susceptibility of the dielectric medium.
    • The polarized dielectric modifies the original external field inside it.
    • At the surfaces of the dielectric normal to the electric field, there is a net charge density.

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    Description

    This quiz covers fundamental concepts in electrostatics, including work done by external forces, electrostatic potential, and the potential due to point charges. Understand how potential energy is stored and the behavior of conductors in electrostatic fields.

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