Physics: Dielectric Materials and Relative Permittivity
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Questions and Answers

What is the name of the insulating medium separating charged surfaces?

  • Capacitor
  • Conductor
  • Dielectric (correct)
  • Electrostatic

    • What is the absolute permittivity of vacuum or free space?

  • 20 × 10⁻¹² F/m
  • 10 × 10⁻¹² F/m
  • 8.854 × 10⁻¹² F/m (correct)
  • 5 × 10⁻¹² F/m

    • What is the relative permittivity of a medium with respect to vacuum?

  • 2
  • 5
  • 0.5
  • 1 (correct)

    • What is the formula to calculate the absolute permittivity of a medium?

    <p>ε = ε₀ × εᵣ</p> Signup and view all the answers

    What is the first law of electrostatics?

    <p>Like charges of electricity repel each other</p> Signup and view all the answers

    What is Coulomb's law?

    <p>The force exerted between two point charges is proportional to each charge and inversely proportional to the square of the distance between them</p> Signup and view all the answers

    What is the value of Coulomb's constant?

    <p>9 × 10⁻¹⁰</p> Signup and view all the answers

    What is the definition of 1 coulomb?

    <p>The charge that flows through a cross-sectional area of 1 meter² in 1 second</p> Signup and view all the answers

    What determines the value of the capacitance?

    <p>The surface area of the plates, the spacing between the plates, and the permittivity of the material</p> Signup and view all the answers

    What is the branch of science that deals with the phenomena associated with electricity at rest?

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

    What is the result of a deficiency of electrons in a body?

    <p>Positive electrification</p> Signup and view all the answers

    What is the total deficiency or excess of electrons in a body known as?

    <p>Its charge</p> Signup and view all the answers

    What is the ratio of electric flux density to electric field strength in a vacuum?

    <p>ε0</p> Signup and view all the answers

    What is the permittivity of a material that indicates its insulating power compared with that of vacuum?

    <p>Relative permittivity (εr)</p> Signup and view all the answers

    What is the formula for the capacitance of a parallel-plate capacitor?

    <p>C = εA / d</p> Signup and view all the answers

    What is the effect of increasing the surface area of the plates on the capacitance?

    <p>It increases the capacitance</p> Signup and view all the answers

    What is the primary function of a capacitor?

    <p>To store energy in its electric field</p> Signup and view all the answers

    What is the most common application of capacitors?

    <p>Electronics and communications</p> Signup and view all the answers

    What is the unit of capacitance?

    <p>Farad (F)</p> Signup and view all the answers

    What is the definition of capacitance?

    <p>The amount of charge stored per plate for a unit voltage difference</p> Signup and view all the answers

    What determines the capacitance of a capacitor?

    <p>The physical dimensions of the capacitor</p> Signup and view all the answers

    What is the formula for capacitance?

    <p>q = Cv</p> Signup and view all the answers

    What is the relationship between capacitance and voltage?

    <p>Capacitance is directly proportional to voltage</p> Signup and view all the answers

    What is the purpose of the dielectric material in a capacitor?

    <p>To separate the plates and prevent arcing</p> Signup and view all the answers

    What is the relationship between electric field strength and distance between plates when there is negligible fringing?

    <p>E=V/d</p> Signup and view all the answers

    What is dielectric strength?

    <p>The maximum amount of field strength that a dielectric can withstand</p> Signup and view all the answers

    What is the unit of electric flux density?

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

    What is the force of repulsion between two similar charges in air, when one coulomb of charge is placed?

    <p>9× 10^9 N</p> Signup and view all the answers

    What is the formula for energy stored in a capacitor?

    <p>W=C/2*V^2</p> Signup and view all the answers

    What is the relative permittivity of water?

    <p>81</p> Signup and view all the answers

    What is the electric field strength when two parallel plates are spaced 0.8mm apart and have a p.d. of 200 V between them?

    <p>250 MV/m</p> Signup and view all the answers

    What is the electric field around a charged particle?

    <p>A spherical region of attractive and repulsive forces</p> Signup and view all the answers

    What is the capacitance of a capacitor when it is charged to 1.25 kV and has a dielectric strength of 50 MV/m?

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

    What can happen if the stress caused by a charge is too large?

    <p>Electrical rupture of the medium</p> Signup and view all the answers

    What is the electric flux density when two parallel rectangular plates carry an electric charge of 0.2 µC?

    <p>0.1 C/m²</p> Signup and view all the answers

    What is the electric field also known as?

    <p>Electrostatic field</p> Signup and view all the answers

    What is the p.d. between the plates when a direct current of 4 A flows into a previously uncharged 20 µF capacitor for 3 ms?

    <p>24 V</p> Signup and view all the answers

    What represents the stress in an electric field?

    <p>Imaginary lines of forces</p> Signup and view all the answers

    What is the region where test charges experience attractive or repulsive forces?

    <p>Electric field</p> Signup and view all the answers

    What can be calculated using the concept of one coulomb of charge?

    <p>Electrostatic force of repulsion</p> Signup and view all the answers

    Study Notes

    Dielectric and Relative Permittivity

    • A dielectric is an insulating medium that separates charged surfaces.
    • Dielectric materials have high resistivities and are used to separate conductors at different potentials.
    • Relative permittivity (εr) is a measure of a dielectric's insulating power compared to that of vacuum.
    • εr = 1 for vacuum, and its value varies for different materials (e.g., air = 1, water = 81, paper = 2-3, glass = 5-10, mica = 2.5-6).

    Absolute Permittivity

    • Absolute permittivity (ε0) is a constant that represents the permittivity of vacuum (ε0 = 8.854 × 10^−12 F/m).
    • ε0 is used as a reference medium to measure the permittivity of other materials.

    Capacitors and Capacitance

    • A capacitor is a passive element that stores energy in its electric field.
    • Capacitors are used extensively in electronics, communications, computers, and power systems.
    • Capacitance (C) is the ratio of the charge on one plate to the voltage difference between the two plates (C = Q/V).
    • The unit of capacitance is the farad (F), where 1 F = 1 C/V.

    Laws of Electrostatics

    • The First Law of Electrostatics states that like charges repel each other, whereas unlike charges attract each other.
    • The Second Law of Electrostatics (Coulomb's Law) states that the force between two point charges is proportional to the product of their strengths and inversely proportional to the square of the distance between them.
    • Coulomb's Law equation: F = Q1Q2 / (4πε0εr d^2)

    Factors Affecting Capacitance

    • The value of capacitance depends on three factors:
      1. The surface area of the plates (larger area, greater capacitance)
      2. The spacing between the plates (smaller spacing, greater capacitance)
      3. The permittivity of the material (higher permittivity, greater capacitance)

    Electrostatics and Permittivity

    • Electrostatics is the branch of science that deals with the phenomena associated with electricity at rest.
    • Permittivity (ε) is a measure of a material's ability to store electric charge.
    • Permittivity is a critical factor in determining the capacitance of a material.

    Electric Field and Electric Field Strength

    • An electric field is a region around a charged particle where test charges experience attractive or repulsive forces.
    • Electric field strength (E) is the force per unit charge at a given point in an electric field.
    • Electric field strength can be calculated using the equation: E = V/d, where V is the voltage and d is the distance between the plates.

    Energy Stored in Capacitors

    • The energy stored in a capacitor is given by the equation: W = (1/2)CV^2, where C is the capacitance and V is the voltage.
    • Energy stored in a capacitor can be dissipated in a time, resulting in an average power developed.

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    Capacitors and Capacitance PDF

    Description

    This quiz explores the properties of dielectric materials, their high resistivities, and their use in separating conductors. It also covers the concept of relative permittivity and its measurement in vacuum.

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