Plasma Physics Quiz
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Questions and Answers

Which of the following is NOT a characteristic of plasma?

  • Conducts electricity.
  • Is always found in a solid state. (correct)
  • Exhibits collective behavior.
  • Responds to electromagnetic fields.

    • What does the plasma parameter, Λ, represent?

  • The ratio of the number of electrons to the number of protons in a plasma.
  • The number of charged particles within a Debye sphere surrounding a given charged particle. (correct)
  • The frequency of collisions between electrons and neutral particles.
  • The ratio of the Debye length to the physical size of the plasma.

    • What is the primary reason why electrons move in a conductor with drift velocity when an electric field is applied?

  • The electric field creates a potential difference, causing electrons to move from higher potential to lower potential.
  • The electric field forces the electrons to accelerate constantly in the direction of the field.
  • The collisions between electrons and atoms in the conductor create a net drift velocity in the direction of the force. (correct)
  • The electrons are naturally attracted to the positive pole of the electric field, causing a net movement.

    • What is the Debye length?

    <p>The distance over which the electrostatic influence of a charged particle is screened by other charged particles. (A)</p> Signup and view all the answers

    What is the relationship between the direction of electron current and conventional current?

    <p>They are always in opposite directions. (B)</p> Signup and view all the answers

    What is the significance of the plasma parameter (Λ) being sufficiently high?

    <p>It ensures that the plasma is quasineutral. (B)</p> Signup and view all the answers

    What does the electron plasma frequency (ωp) represent?

    <p>The frequency of oscillations of electrons in a plasma. (B)</p> Signup and view all the answers

    What happens to the energy provided by the applied electric field in the conductor?

    <p>Most of the energy is lost as heat due to collisions between electrons and atoms. (B)</p> Signup and view all the answers

    What characterizes the movement of the charge carriers in equilibrium within a metal?

    <p>They move randomly with no net motion. (C)</p> Signup and view all the answers

    Which of the following is NOT a condition for the plasma approximation to hold?

    <p>The Debye length is much larger than the physical size of the plasma. (B)</p> Signup and view all the answers

    How is the current defined in a given cross-sectional area of a conductor?

    <p>The net amount of charge flowing through the area per unit time. (D)</p> Signup and view all the answers

    What is the typical pressure in a plasma globe?

    <p>Below 0.01 atm. (A)</p> Signup and view all the answers

    Which of the following is NOT a characteristic of the high-frequency alternating current used in plasma globes?

    <p>Direct current, not alternating current. (B)</p> Signup and view all the answers

    What is the SI unit for current?

    <p>Ampere (A) (C)</p> Signup and view all the answers

    Which of the following statements is true about the drift velocity of electrons in a conductor?

    <p>It is typically very small compared to the thermal velocity of electrons. (A)</p> Signup and view all the answers

    What is the primary reason for the increase in temperature of a conductor when carrying current?

    <p>The energy gained by the electrons from the electric field is converted into heat. (D)</p> Signup and view all the answers

    What happens when a charged object is touched?

    <p>The charge on the object is transferred to the object it is touched with. (A)</p> Signup and view all the answers

    Why is the earth considered a good conductor?

    <p>Because it contains water and ions. (C)</p> Signup and view all the answers

    According to Coulomb's Law, what happens to the electric force between two point charges as the distance between them increases?

    <p>The force decreases. (A)</p> Signup and view all the answers

    What is the SI unit of electric charge?

    <p>Coulomb (C) (A)</p> Signup and view all the answers

    Which of the following is NOT true about Coulomb's Law?

    <p>The force between two charges is always attractive. (D)</p> Signup and view all the answers

    What is the value of the proportionality constant 'k' in Coulomb's Law?

    <p>8.988 × 10^9 N ∙ m^2/C^2 (C)</p> Signup and view all the answers

    What is the typical range of charge in Coulombs?

    <p>10^-6 C to 10^-9 C (A)</p> Signup and view all the answers

    Why is grounding important for objects such as circuits and appliances?

    <p>To prevent the buildup of charge on them. (C)</p> Signup and view all the answers

    What is the relationship between the electric field (E) within a dielectric and the surface charge density (𝜎) on the capacitor plate?

    <p>E is directly proportional to 𝜎, with a proportionality constant of 𝜖. (D)</p> Signup and view all the answers

    What is the capacitance of a parallel-plate capacitor with a dielectric between the plates?

    <p>𝐶 = 𝐾𝐴𝜖0 / 𝑑 (C)</p> Signup and view all the answers

    What is the electric energy density (𝑢) in a dielectric?

    <p>𝑢 = 1/2 K𝜖0E^2 (D)</p> Signup and view all the answers

    What is the permittivity (𝜖) of a dielectric?

    <p>The product of the dielectric constant (K) and the permittivity of free space (𝜖0). (D)</p> Signup and view all the answers

    What is the total charge enclosed (𝑄𝑒𝑛𝑐𝑙) by a Gaussian surface in a dielectric?

    <p>The difference between the free charge (𝑄𝑒𝑛𝑐𝑙−𝑓𝑟𝑒𝑒) and the induced charge (𝜎𝑖𝐴) on the dielectric surface. (C)</p> Signup and view all the answers

    How does the electric field (E) change when a dielectric material is inserted between the plates of a capacitor?

    <p>The electric field decreases by a factor of K. (A)</p> Signup and view all the answers

    What is dielectric breakdown?

    <p>The process of a dielectric becoming a conductor when subjected to a sufficiently strong electric field. (B)</p> Signup and view all the answers

    What is the relationship between the induced surface charge density (𝜎𝑖) and the surface charge density (𝜎) on the capacitor plate?

    <p>𝜎𝑖 is directly proportional to 𝜎, with a proportionality constant of 1/K. (C)</p> Signup and view all the answers

    What is the potential difference across a real source in a circuit?

    <p>Less than the emf (B)</p> Signup and view all the answers

    What is the terminal voltage of a real source of emf when no current is flowing through it?

    <p>Equal to the emf (D)</p> Signup and view all the answers

    What is the relationship between the emf, current, and internal resistance of a real source?

    <p>𝑉𝑎𝑏 = ℰ − 𝐼𝑟 (B)</p> Signup and view all the answers

    What is the power delivered to a pure resistor by the circuit?

    <p>𝑃 = 𝐼 2 𝑅 (B), 𝑃 = 𝑉𝑎𝑏 2 / 𝑅 (C), 𝑃 = 𝑉𝑎𝑏𝐼 (D)</p> Signup and view all the answers

    What does the term 'power rating' of a resistor refer to?

    <p>The maximum power the resistor can dissipate without overheating (D)</p> Signup and view all the answers

    In a complete circuit, what is the relationship between the emf and the potential drop across the external circuit?

    <p>They are equal and in the same direction (A)</p> Signup and view all the answers

    What is the rate at which energy is transferred either into or out of a circuit element?

    <p>𝑃 = 𝑉𝑎𝑏𝐼 (C)</p> Signup and view all the answers

    What is the current in a circuit with emf ℰ, external resistance R, and internal resistance r?

    <p>𝐼 = ℰ / (𝑅 + 𝑟) (B)</p> Signup and view all the answers

    What is the key characteristic of ferroelectric materials?

    <p>They exhibit a spontaneous electric polarization that can be reversed by an external electric field. (C)</p> Signup and view all the answers

    Which of the following materials exhibits piezoelectricity and is used in medical imaging?

    <p>Lead zirconate titanate (PZT) (A)</p> Signup and view all the answers

    What is the primary cause of the piezoelectric effect in crystals?

    <p>The regular atomic structure within the crystal. (B)</p> Signup and view all the answers

    Which of the following statements accurately describes Coulomb's Law?

    <p>It states that the force between two charges is proportional to the product of their charges and inversely proportional to the square of the distance between them. (D)</p> Signup and view all the answers

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

    <p>It increases the capacitance of the device. (C)</p> Signup and view all the answers

    Which of the following is NOT a characteristic of a conservative force?

    <p>The work done by the force is path-dependent. (D)</p> Signup and view all the answers

    When discussing electric charges, what is the meaning of potential, V?

    <p>The work done per unit charge to move a charge from one point to another. (D)</p> Signup and view all the answers

    What determines the capacitance of a capacitor?

    <p>All of the above. (D)</p> Signup and view all the answers

    Study Notes

    Physics 1: Electrostatic Field and Electric Current

    • The course is Physics 1, taught by Dr. Kristina Bočkutė at KTU (Kaunas University of Technology)
    • The course covers electrostatic fields, electric current, and related topics.

    Minutes from the Last Lecture

    • Ideal gas model: pV = nRT
    • Thermodynamic processes: Isothermal, isochoric, isobaric, pV diagrams
    • First Law of Thermodynamics: A generalization of energy conservation, including heat and mechanical work transfer.
    • Second Law of Thermodynamics: It's impossible to convert all absorbed heat at a single temperature into mechanical work while returning the system to its original state. Heat cannot spontaneously flow from a cold body to a hot body.
    • Third Law of Thermodynamics: A system's entropy approaches a constant value as its temperature approaches absolute zero.

    1st Law of Thermodynamics

    • Increase in internal energy in a gas process: equals the heat input plus the work done on the gas.

    Heat Capacity

    • The heat capacity at constant volume of an ideal gas depends on the number of molecules.

    Pressure and Volume

    • If the pressure of an ideal gas doubles during a process in which the heat given up by the gas equals the work done on the gas, then the volume is halved.

    Outline

    • Electric Charges: Coulomb's law, electrostatic fields, electric dipole, electric flux, Gauss's law, electric potential, capacitors, dielectrics, polarization, and summary.
    • Electric Current: Drift velocity, current, current density, resistivity, resistance, electromotive force (emf), energy, and power.
    • Direct-current circuits: Resistor connections (series and parallel), Kirchhoff's rules.
    • Other Processes: A summary and introduction to next lecture's topics.

    Electric Charge

    • Historical introduction: The ancient Greeks discovered amber (elektron) attracted objects after rubbing.
    • Two types of charge: Positive and negative
    • Charges repelling each other: Like charges repel one another, while unlike charges attract.
    • Structure of an Atom: Atoms consist of negatively charged electrons, positively charged protons, and uncharged neutrons.
    • Mass and charge: The values are listed for electrons (me), protons (mp), and neutrons (mn)
    • Atomic Number: The number of protons or electrons in a neutral atom.
    • Ionization: Removing or adding electrons creates positive or negative ions.
    • Principle of charge conservation: In any closed system the algebraic sum of all electric charges remains constant.
    • Quantization of charge: All observable charges are always integral multiples of a fundamental electric charge e.
    • Coulomb's law: The magnitude of electric force between two point charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.
    • The proportionality constant k is 8.988 × 10^9 N⋅m²/C2

    Electric Charge: Materials

    • Insulators: Materials in which electric charges remain immobile
    • Conductors: Materials through which electric charges can easily move
    • Semiconductors: These lie between good conductors and good insulators.

    Charging

    • Insulators: Charged by rubbing
    • Metals: Charged by contact
    • Charges reside on the surface

    Discharging

    • Touching a charged object dissipates the charge.
    • The Earth is a large conductor
    • Grounding prevents build up of charges

    Electric Field

    • Electric force is long-range, no contact required
    • Electric field : The alteration of space around a charged particle.
    • A force is exerted on a charged particle when it enters the altered space.
    • Electric field units: 1 newton per coulomb (1 N/C).
    • Force on a point charge in an electric field: F = qE
    • The electric field of a point charge always points away from a positive charge and toward a negative one.
    • Electric field due to a point charge: F/q = E
    • E = 1q/(4πεr^2); the unit vector from the point charge toward the measurement;

    Superposition of Electric Fields

    • The total electric field at a point is the vector sum of the fields due to individual charges, just as with forces.
    • Linear, surface, and volume charge density are useful concepts

    Electric Field Lines

    • Electric field lines are imaginary lines used to visualize electric fields.
    • Tangents to the lines at any point indicate the direction of the electric field vector.
    • The spacing of lines gives a visual idea of the field strength.
    • The lines never intersect.

    Electric Dipoles

    • An electric dipole is a pair of equal and opposite charges separated by a distance.
    • The electric dipole moment is a vector quantity pointing from the negative to the positive charge.
    • The magnitude of the dipole moment: is the product of the charge and separation.
    • The torque on a dipole in a uniform electric field is given by M = pEsinθ
    • The position ∅ = 0 is stable equilibrium, and ∅ = π is unstable.
    • The potential energy of an electric dipole in a uniform electric field is given by U = –p⋅E

    Electric Flux

    • Electric flux describes the amount of an electric field passing through a surface.
    • A positive flux indicates outward flux, and a negative flux indicates inward flux.
    • The net electric flux through a closed surface is directly proportional to the net charge enclosed within the surface.

    Calculating Electric Flux

    • Gauss' Law: The net electric flux through a closed surface is directly proportional to the net charge inside that surface.

    Gauss's Law

    • Gauss's law relates the electric field to the total charge enclosed by a surface.
    • A concept that allows calculating fields based on the distribution of charge.

    Electrical Potential Energy

    • The work done by the electric field: is equal to the change in potential energy.
    • The work done by the field does not depend on the path.
    • Work is negative if the movement is in the direction of the field
    • Work is positive if the movement is in the opposite direction.
    • Potential Energy: U = qV
    • Potential Energy is determined relative to zero energy at infinity.
    • Potential Energy due to a collection of point charges: U = (1/4πε) Σ(qiqj/rj)

    Electrical Potential

    • The potential energy per unit of charge (Potential is measured in Volts or Joules/Coulomb.)
    • Potential due to a point charge : V=1q/(4πε0r)
    • Potential of a collection of point charges: V=1/(4πε0) Σ(qi/ri)

    Potential Gradient

    • The potential gradient is the rate of change of potential per unit distance
    • The electric field vector is negative potential gradient: E = –∇V

    A Conductor in Electrostatic Equilibrium

    • Excess charges reside on the surface.
    • The electric field is zero inside the conductor.
    • Any two points inside the conductor have the same potential.
    • The electric field outside the conductor is perpendicular to the surface.

    Sources of Electric Potential

    • A battery creates a potential difference between two terminals, which depends on chemical reactions and transport of ions.
    • The emf is the work per unit charge delivered by the battery.

    Capacitors

    • A capacitor stores electric charge and energy by holding opposite charges on two conductors separated by an insulator.
    • The capacitance is the ratio of charge to the potential difference (C=Q/Vab)
    • Capacitors have SI unit of farads (1F = 1C/V).
    • A greater capacitance holds a greater potential difference given a certain charge.

    Capacitance

    • Parallel-plate capacitor capacitance: C=EA/d (in a vacuum or air; K is a dielectric constant).

    Connection of Capacitors

    • Series Combination: (1/Ceq) = (1/C₁)+(1/C₂)+(1/C₃)+...
    • Parallel Combination: Ceq = C₁+C₂+C₃+...

    Energy Stored in Capacitors

    • U=1/2CV^2
    • U=1/2Q^2/C

    Dielectrics

    • Dielectric materials are insulators inserted between capacitor plates.
    • Increases capacitance over a vacuum
    • Dielectric constant (K) : ratio of capacitance with dielectric to capacitance without.
    • The dielectric constant is always greater than 1.

    Induced Charges and Polarization

    • Induced charges created due to polarization within the dielectric (equal but opposite charges on surfaces of polarized dielectric; net charge =0)
    • Surface charge density due to polarization: σ₂ =(σ–σ₁), The electric field between the plates is related to the net surface charge density; Eo/E = K

    Dielectric Breakdown

    • Dielectric breakdown occurs when a dielectric material fails under strong electric field; the material eventually becomes a conductor.
    • Dielectric strength is the maximum field with no breakdown.

    Gauss's Law in Dielectrics

    Ferroelectricity

    • Ferroelectricity is a property of certain materials in which they possess spontaneous electric polarization that can be reversed.

    Piezoelectricity

    • Piezoelectric materials become charged when compressed.
    • This effect is reversible meaning the crystal generates a voltage when compressed.
    • This effect is also valid in reverse (A voltage causes a physical change/deformation of the material.)

    Electric Discharge

    • Is a flow of electric charge through a liquid, gas, or solid
    • Townsend discharge occurs when free electrons gain energy.
    • Glow discharge happens when the voltage is high enough to initiate Townsend discharge and some electrons are accelerated to the other end and generate light
    • Arc discharge has high current
    • Corona discharge has very small current

    Plasma

    • Plasma is a quasi-neutral gas of charged particles including ions and electrons.
    • Plasma parameters are a criterion expressing the degree of plasma behavior; high Λ corresponds to approximate plasma behavior.
    • Plasma frequency: a measure of the electron oscillations .

    Next Lecture

    • Magnetic fields in materials and a vacuum
    • Electromagnetic Induction

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    Test your knowledge of plasma physics with this engaging quiz! Questions cover key concepts such as plasma parameters, electron motion in conductors, and characteristics of plasma globes. Perfect for students studying physics or anyone interested in the fundamentals of plasma science.

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