Physics Electric Charge Concepts
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Questions and Answers

What is the SI unit of electric charge?

  • Coulomb (correct)
  • Volt
  • Newton
  • Ampere

    • Which statement about electric charges is incorrect?

  • Charge can be created and destroyed. (correct)
  • Charge is additive across different objects.
  • Charges are quantized in integral multiples of elementary charge.
  • Charges are conserved in an isolated system.

    • According to Coulomb's Law, the force between two charges decreases as which of the following increases?

  • The net charge of the system
  • The product of the two charges
  • Distance between the charges (correct)
  • Magnitude of one of the charges

    • What does the electric field represent?

    <p>The force experienced by a positive charge</p> Signup and view all the answers

    Which of the following statements about electric field lines is true?

    <p>Field lines start from positive charges and end at negative charges.</p> Signup and view all the answers

    What is the formula for the electric field due to a point charge?

    <p>E = Kq/r^2</p> Signup and view all the answers

    What is the proportionality constant 'K' in Coulomb's Law?

    <p>9 x 10^9 Nm^2/C^2</p> Signup and view all the answers

    If a system has a net charge of zero, which statement is true?

    <p>There are equal positive and negative charges.</p> Signup and view all the answers

    What is the SI unit of electric flux?

    <p>Nm<sup>2</sup>/C</p> Signup and view all the answers

    What is the primary purpose of electric field lines?

    <p>To map the direction of the electric field between charges</p> Signup and view all the answers

    According to Gauss's Law, the total flux through a closed surface is proportional to what?

    <p>Net charge enclosed by the surface</p> Signup and view all the answers

    What does Gauss's Law relate to in electrostatics?

    <p>The relationship between electric flux and the net charge within a surface</p> Signup and view all the answers

    Which statement accurately describes a semiconductor?

    <p>Offer variable conductivity that can be adjusted</p> Signup and view all the answers

    Which statement correctly describes the electric field due to an infinite charged sheet?

    <p>The electric field is uniform and does not change with distance.</p> Signup and view all the answers

    What is the electric field inside a hollow spherical shell?

    <p>0</p> Signup and view all the answers

    What happens during the process of earthing?

    <p>Excess charge is allowed to flow to the ground</p> Signup and view all the answers

    How does the force between two charged bodies change with distance?

    <p>It varies quadratically with the distance between charges</p> Signup and view all the answers

    What is the formula for the electric field due to an infinite straight wire?

    <p>E = λ / 2πε<sub>o</sub>r</p> Signup and view all the answers

    How is the electric field due to a point charge expressed?

    <p>E = q / 4πε<sub>o</sub>r<sup>2</sup></p> Signup and view all the answers

    What charge corresponds to 1 Coulomb in terms of the number of electrons?

    <p>6.25 x 10<sup>18</sup></p> Signup and view all the answers

    Which of the following describes the relationship of electric field due to a spherical shell outside the shell?

    <p>E α 1/r<sup>2</sup></p> Signup and view all the answers

    What is the definition of the electric dipole moment?

    <p>The distance between two charges multiplied by the charge of one of the charges.</p> Signup and view all the answers

    In an electric dipole, how is the direction of the dipole moment defined?

    <p>From positive to negative charge.</p> Signup and view all the answers

    What is the expression for the net electric field at an axial point due to a dipole?

    <p>$E_{net} = Kq(4a)/(r^3)$</p> Signup and view all the answers

    What is the behavior of the electric field lines in a uniform electric field?

    <p>They are straight, parallel, and uniformly spaced.</p> Signup and view all the answers

    At which angle is the torque on a dipole in a uniform electric field maximized?

    <p>90°</p> Signup and view all the answers

    What is the relationship between the electric field at the axial and equatorial points of a dipole?

    <p>E_{axial} = 2E_{eq}</p> Signup and view all the answers

    What is the torque on a dipole when the angle between the dipole moment and the electric field is 0°?

    <p>Zero torque.</p> Signup and view all the answers

    Under what condition can the strength of the electric field at an equatorial point of a dipole be approximated as $E_{eq} = -kp/r^3$?

    <p>When r is much greater than a.</p> Signup and view all the answers

    How many electrons are transferred when a charge of 3 x 10-7 C is obtained?

    <p>1.875 x 10<sup>12</sup></p> Signup and view all the answers

    What is the mass of electrons transferred when 1.875 x 1012 electrons are involved?

    <p>17 x 10<sup>-19</sup> kg</p> Signup and view all the answers

    Given a charge of 8 x 10-18 C, how many electrons would this represent?

    <p>50</p> Signup and view all the answers

    What force exists between two charges of 2 x 10-7 C and 3 x 10-7 C placed 30 cm apart?

    <p>6.00 x 10<sup>-3</sup> N</p> Signup and view all the answers

    If the separation between two charges is doubled, how does the force change?

    <p>Decreases by a factor of 4</p> Signup and view all the answers

    What distance is computed when a force of 0.2 N is acting between two charges of 0.4 µC and -0.8 µC?

    <p>12 cm</p> Signup and view all the answers

    What is the equivalent force on the second sphere due to the first if the force on the first sphere is 0.2 N?

    <p>0.2 N</p> Signup and view all the answers

    What is the value of k used in the force equation for two point charges in air?

    <p>9 x 10<sup>9</sup></p> Signup and view all the answers

    What happens to the force between two charges if the distance is increased by a factor of 3?

    <p>It becomes 1/9 of the original force</p> Signup and view all the answers

    Which of the following statements about dielectric constant (K) is correct?

    <p>K is greater than 1 for most materials other than air</p> Signup and view all the answers

    What is the primary characteristic of conductors?

    <p>They contain large numbers of free electrons</p> Signup and view all the answers

    Which charging method involves direct contact between materials?

    <p>Charging by Contact</p> Signup and view all the answers

    How does earthing affect a charged body?

    <p>It allows the body to share excess charge with the earth</p> Signup and view all the answers

    What type of body has an equal number of positive and negative charges?

    <p>Neutral body</p> Signup and view all the answers

    What defines an insulator in terms of its electron behavior?

    <p>Electrons are tightly bound to their atoms</p> Signup and view all the answers

    Which of the following statements is true regarding Coulomb's Law?

    <p>The force can be both attractive and repulsive depending on the charge signs</p> Signup and view all the answers

    Study Notes

    Electric Charge

    • Charge is a property of matter, causing electrostatic force.
    • Symbol: q or Q
    • SI Unit: Coulomb (C)
    • Dimension: [AT]
    • Types: positive (+ve) and negative (-ve)

    Properties of Charge

    • Additive: The total charge is the sum of all charges.
    • Quantized: Charges are multiples of elementary charge (e = 1.6 × 10⁻¹⁹ C).
    • Conserved: In an isolated system, the net charge remains constant.

    Coulomb's Law

    • The force between two charges is directly proportional to the product of their magnitudes and inversely proportional to the square of the distance between them.
    • Formula: F = k * q₁ * q₂ / r²
    • k = 9 × 10⁹ Nm²/C²
    • r = distance between charges
    • q₁ and q₂ = magnitudes of the charges

    Dielectric Constant

    • Represents the ratio of the force between two charges in a medium to the force between the same charges in vacuum.
    • K = 1 for vacuum/air
    • K > 1 for other mediums
    • Formula: Fₘ = Fₐᵢᵣ / K

    Electric Field

    • The force experienced by a unit positive charge at a point.
    • Vector quantity
    • SI Unit: N/C
    • Formula: E = F / q

    Electric Field due to a Point Charge

    • Formula: E = k * q / r²

    Direction of Electric Field

    • From a positive charge, away.
    • Towards a negative charge.

    Torque on Dipole in Uniform Electric Field

    • Formula: τ = p * E * sin θ
    • p = dipole moment
    • E = electric field strength
    • θ = angle between p and E

    Electric Flux

    • Represents the measure of the electric field passing through a surface.
    • Formula: Φ = ∫E ⋅ dA (surface integral)
    • SI Unit: Nm²/C

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