Physics Chapter on Electric Forces
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Questions and Answers

What is the nature of the force between a charged object and a neutral object?

  • Electrostatic
  • Inertial
  • Attractive (correct)
  • Repulsive

    • When the charged rod is removed after touching, which charge configuration is possible for the spheres?

  • Q1 is positive and Q2 is negative (correct)
  • Q1 is positive and Q2 is positive
  • Q1 is neutral and Q2 is positive
  • Q1 is negative and Q2 is negative

    • What does Coulomb's Law state about the relationship between force and charge separation?

  • Force increases with an increase in charge separation
  • Force is exponentially related to charge separation
  • Force is independent of charge separation
  • Force decreases with an increase in charge separation (correct)

    • What happens to the charges of spheres 1 and 2 when they are separated after being in contact near a charged rod?

    <p>One sphere becomes positively charged and the other negatively charged</p> Signup and view all the answers

    What is the formula for the force between two charges according to Coulomb's Law?

    <p>$F = k \frac{Q_1 Q_2}{r^2}$</p> Signup and view all the answers

    What does the constant of proportionality 'k' depend on in Coulomb's Law?

    <p>Medium in which the charges are located</p> Signup and view all the answers

    How does Coulomb's Law compare to Newton's Law of Gravitation in terms of force dependence?

    <p>Both are inversely proportional to the square of distance</p> Signup and view all the answers

    What occurs to molecular ions during the charging process?

    <p>Bonds are broken, creating charged fragments</p> Signup and view all the answers

    What happens to the electric field when a positive test charge is placed near a negative source charge?

    <p>The electric field points toward the negative charge.</p> Signup and view all the answers

    How is the electric field strength at a distance expressed mathematically for a point charge?

    <p>$E = \frac{Q}{4\pi\epsilon_{0}r^2}$</p> Signup and view all the answers

    When finding the resultant electric field from multiple charges, which is the first step in the calculation?

    <p>Calculate the electric field due to each charge separately.</p> Signup and view all the answers

    What is the unit of measurement for the electric field strength?

    <p>Newtons per Coulomb</p> Signup and view all the answers

    At a point 30 cm to the right of a charge Q = -3.0 x 10-6 C, how does the magnitude of the electric field compare to that at 60 cm from the same charge?

    <p>The electric field is stronger at 30 cm than at 60 cm.</p> Signup and view all the answers

    If a charge experiences an electric force $F_{e}$ in an electric field $E$, the relationship between these quantities is given by which equation?

    <p>$F_{e} = qE$</p> Signup and view all the answers

    What is the direction of the electric field lines in relation to a positive point charge?

    <p>They originate from the positive charge and end at infinity.</p> Signup and view all the answers

    In the context of electric fields, what is meant by the term 'test charge'?

    <p>A small charge used to probe the electric field without affecting it.</p> Signup and view all the answers

    What is the permittivity of free space (vacuum)?

    <p>$8.85418781762 × 10^{-12} ext{ C}^2/ ext{N} ext{m}^2$</p> Signup and view all the answers

    How does the permittivity of water compare to that of free space?

    <p>It is approximately 80 times that of free space.</p> Signup and view all the answers

    What is the formula for Coulomb's law?

    <p>$F = k \cdot \frac{Q_1 Q_2}{r^2}$</p> Signup and view all the answers

    What can be concluded about the comparison of electric force to gravitational force in a hydrogen atom?

    <p>The gravitational force is negligible compared to the electric force.</p> Signup and view all the answers

    If Q1 = 50 μC and Q2 = 1 μC are separated by a distance of 0.50 m, which force calculation is used for the force that Q1 exerts on Q2?

    <p>$F_{Q1} = k \cdot \frac{Q1 Q2}{(0.50)^2}$</p> Signup and view all the answers

    What is the relationship between the magnitudes of electric and gravitational forces between the electron and proton?

    <p>Electric force is 2 × 10^39 times greater than gravitational force.</p> Signup and view all the answers

    Which of the following is NOT a correct application of Coulomb's law?

    <p>Understanding the behavior of masses in gravitational fields.</p> Signup and view all the answers

    What can be inferred about the forces acting on particle 3 due to other charges in an aligned configuration?

    <p>The net force on particle 3 must be calculated by considering all other charges.</p> Signup and view all the answers

    What does the equation $ΔU = U_2 - U_1 = - ∫ F ullet dl$ represent in the context of conservative forces?

    <p>The change in electric potential energy due to the work done by electric force.</p> Signup and view all the answers

    What is the total electric flux through a closed surface due to a charge Q enclosed within it?

    <p>It is equal to the enclosed charge divided by permittivity.</p> Signup and view all the answers

    In a uniform electric field between parallel plates, what is true about the electric force acting on a charge?

    <p>It is constant everywhere in the field.</p> Signup and view all the answers

    If a positive charge is replaced with a negative charge of the same magnitude, how does the total electric flux change?

    <p>The total electric flux becomes negative.</p> Signup and view all the answers

    Which statement correctly describes the relationship between work and potential energy?

    <p>Work done against a conservative force increases potential energy.</p> Signup and view all the answers

    If the electric potential energy between two points is given by $ΔU_E = U_b - U_a = - ∫_a^b F_E ullet dl$, what does this integral represent?

    <p>The total work done by the electric field moving from point a to b.</p> Signup and view all the answers

    What is the relationship between the total electric flux and the surface area of the Gaussian surface when the charge is at its center?

    <p>Total electric flux is independent of the surface area.</p> Signup and view all the answers

    What is the significance of defining a point as zero potential energy in an electric field?

    <p>It allows for a consistent reference for measuring potential energy.</p> Signup and view all the answers

    What happens to the total electric flux when the charge is not at the center of the enclosed surface?

    <p>The total electric flux remains unchanged.</p> Signup and view all the answers

    When calculating changes in electric potential energy, how is the electric field involved in the calculation?

    <p>It is calculated as the gradient of potential energy.</p> Signup and view all the answers

    In Gauss's Law, what does the symbol 𝜖 represent?

    <p>Permittivity of free space</p> Signup and view all the answers

    Which expression correctly represents the electric field strength between two parallel plates when the potential difference is known?

    <p>$E = \frac{V}{d}$ where V is voltage and d is distance between plates.</p> Signup and view all the answers

    Which factor is essential for applying Gauss's Law effectively?

    <p>Spherical symmetry of the charge distribution</p> Signup and view all the answers

    What is the total electric flux through the surface of a sphere with radius 10 cm enclosing a charge of 1.2 nC?

    <p>$3.41 \times 10^{-8}$ C</p> Signup and view all the answers

    What is the role of electric potential energy in relation to electric fields and charges?

    <p>It quantifies the work done on a charge when moved within an electric field.</p> Signup and view all the answers

    When considering electric fields, what convention is used for determining the sign of electric flux?

    <p>Positive flux for outward field direction.</p> Signup and view all the answers

    Study Notes

    Polarization force

    • Polarization force is always attractive between a charged object and a neutral one.

    Coulomb's Law

    • Coulomb's Law describes the force between two electrically charged bodies.
    • The force is inversely proportional to the square of the distance between the charges and proportional to the product of their charges.
    • The constant of proportionality (k) in a vacuum is given by: 𝑘= 1 / 4𝜋𝜀
      • 𝜖 is the permittivity of the medium.
      • For vacuum (free space), 𝜀𝑜 = 8.85418781762 × 10−12 𝐶2/𝑁 ∙ 𝑚2
      • For practical calculations in vacuum, we can simplify 𝑘= 1/4𝜋𝜀𝑜 = 8.99 × 109 𝑁 ∙ 𝑚2/𝐶2
    • Coulomb's Law can be expressed as: 𝐹 = 1 / 4𝜋𝜀𝑜 * (𝑄1𝑄2 / 𝑟2)

    Comparison of Gravitational and Electric forces

    • Electric force is much stronger than gravitational force.
    • The electric force between an electron and a proton in a hydrogen atom is about 2 × 1039 times stronger than the gravitational force between them.

    Gauss's Law

    • The electric flux Φ𝐸 through a closed surface (Gaussian surface) is proportional to the net charge enclosed within the surface.
    • Gauss's Law is given by: Φ𝐸 = ර𝐸.𝑑𝐴Ԧ = 𝑄𝑒𝑛𝑐 / 𝜖
    • 𝜖 is the permittivity of the medium.
    • Gauss's Law can be used to find the electric field for charge distributions.
    • However, the application of Gauss's Law is limited to highly symmetric electric fields.

    Electric Flux

    • Electric flux is the measure of the electric field passing through a given surface.
    • It is calculated by integrating the electric field over the surface area.
    • Convention:
      • Flux leaving the enclosed volume is positive.
      • Flux entering the enclosed volume is negative.
    • This convention is consistent with the electric field pointing away from positive charges and towards negative charges.

    Electric Field

    • Defined as the force experienced by a unit positive test charge at a point.
    • The electric field is a property of the source charge and is independent of the test charge.
    • Can be represented by field lines that start on positive charges and end on negative charges.

    Electric Potential Energy

    • The potential energy of a charge q in an electric field is given by: Δ𝑈𝐸 = 𝑈2 − 𝑈1 = − ∫1^2 𝐹𝑬.d𝑙Ԧ
    • It is the work done by the electric force when moving the charge from one point to another in the field.
    • Defined with reference to a zero potential energy point, usually at infinity.

    Electric Potential

    • Electric potential is the potential energy per unit charge at a point in an electric field.
    • Measured in volts (V).
    • Related to electric field by: 𝐸𝑟 = −d𝑉/d𝑟

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    Description

    This quiz covers key concepts in electrostatics, including polarization force, Coulomb's Law, and Gauss's Law. Additionally, it compares the electric and gravitational forces, illustrating the significant differences between them. Test your understanding of these fundamental principles of physics.

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