Dielectric constant – determination and applications MCQs With Answer

Dielectric constant – determination and applications MCQs With Answer

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Dielectric constant – determination and applications MCQs With Answer

The dielectric constant (relative permittivity) is a fundamental property describing how materials respond to electric fields, critical in pharmaceutical sciences for understanding solvent polarity, drug–excipient interactions, solvation, and formulation stability. B. Pharm students should learn experimental determination methods — capacitance measurements, impedance/dielectric spectroscopy, and bridge techniques — plus interpretation: frequency and temperature dependence, dielectric loss (tanδ), and relaxation phenomena. Applications include monitoring crystallization, polymorphism, hydration, drug release profiling, and excipient selection. This focused set of MCQs emphasizes both theory and practical laboratory considerations to strengthen formulation and analytical skills. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the dielectric constant (relative permittivity) of a material?

  • The ratio of the material’s permittivity to vacuum permittivity
  • The electrical conductivity divided by permittivity
  • The capacitance of a material per unit area
  • The inverse of dielectric loss

Correct Answer: The ratio of the material’s permittivity to vacuum permittivity

Q2. Which equation relates capacitance C of a parallel plate capacitor to dielectric constant εr?

  • C = ε0 * A / d
  • C = εr * ε0 * A / d
  • C = d / (εr * ε0 * A)
  • C = εr / (ε0 * A * d)

Correct Answer: C = εr * ε0 * A / d

Q3. What is the approximate dielectric constant of pure water at room temperature (~20–25°C)?

  • ~2
  • ~10
  • ~80
  • ~0.5

Correct Answer: ~80

Q4. Which instrument is commonly used to measure dielectric properties over a wide frequency range?

  • UV-Vis spectrophotometer
  • Impedance analyzer / dielectric spectrometer
  • Polarimeter
  • Gas chromatograph

Correct Answer: Impedance analyzer / dielectric spectrometer

Q5. Dielectric loss (ε”) mainly indicates which property of a material?

  • Ability to store electrical energy
  • Ability to dissipate electrical energy as heat
  • Mechanical rigidity
  • Optical transparency

Correct Answer: Ability to dissipate electrical energy as heat

Q6. The loss tangent (tanδ) is defined as:

  • tanδ = ε’ × ε”
  • tanδ = ε” / ε’
  • tanδ = ε’ / ε”
  • tanδ = ε’ + ε”

Correct Answer: tanδ = ε” / ε’

Q7. Which polarization mechanism is dominant at optical frequencies?

  • Orientation (dipolar) polarization
  • Interfacial (Maxwell–Wagner) polarization
  • Electronic polarization
  • Space charge polarization

Correct Answer: Electronic polarization

Q8. Maxwell–Wagner polarization is most important in:

  • Homogeneous single-component gases
  • Heterogeneous systems and interfaces (e.g., suspensions, emulsions)
  • Pure electronic crystals at optical frequencies
  • Vacuum

Correct Answer: Heterogeneous systems and interfaces (e.g., suspensions, emulsions)

Q9. The Clausius–Mossotti relation links dielectric constant to:

  • Molar refractivity only
  • Molecular polarizability and density
  • Viscosity of the medium
  • Boiling point of a solvent

Correct Answer: Molecular polarizability and density

Q10. Which of the following factors decreases the dielectric constant of a solvent?

  • Increasing temperature (for polar solvents)
  • Increasing polarity of solvent molecules
  • Increasing hydrogen bonding network
  • Adding highly polar solutes

Correct Answer: Increasing temperature (for polar solvents)

Q11. In dielectric spectroscopy, a relaxation peak corresponds to:

  • A phonon vibration with no relation to molecules
  • Dipolar reorientation or relaxation process at a characteristic time
  • Permanent chemical degradation
  • Static conductivity only

Correct Answer: Dipolar reorientation or relaxation process at a characteristic time

Q12. For a parallel plate capacitor with area 1 m², plate separation 1 m, vacuum permittivity ε0 = 8.854×10⁻¹² F/m, and measured capacitance C = 8.854×10⁻11 F, what is the dielectric constant εr?

  • 0.1
  • 1
  • 10
  • 100

Correct Answer: 10

Q13. Which dielectric model describes a single exponential relaxation (ideal dipolar relaxation)?

  • Cole–Cole model
  • Debye model
  • Cole–Davidson model
  • Havriliak–Negami model

Correct Answer: Debye model

Q14. Dielectric spectroscopy can be applied in B.Pharm to monitor:

  • Polymorphic transitions and crystallization kinetics
  • Only color change in tablets
  • Gas permeability of packaging exclusively
  • Protein primary sequence

Correct Answer: Polymorphic transitions and crystallization kinetics

Q15. Which type of polarization contributes at low frequencies (Hz–kHz) in heterogeneous pharmaceutical formulations?

  • Electronic polarization
  • Interfacial or space charge polarization
  • Atomic polarization only
  • None — only conductivity matters

Correct Answer: Interfacial or space charge polarization

Q16. A high dielectric constant solvent generally indicates:

  • Low polarity and poor solvation of ionic drugs
  • High polarity and good ability to stabilize charges
  • That solvent is nonpolar and hydrophobic
  • Extremely low boiling point

Correct Answer: High polarity and good ability to stabilize charges

Q17. Which parameter is most affected by ionic conductivity during dielectric measurements?

  • Real part of permittivity (ε’) only
  • Imaginary part of permittivity (ε”) and low-frequency dispersion
  • Refractive index only
  • None — conductivity has no effect

Correct Answer: Imaginary part of permittivity (ε”) and low-frequency dispersion

Q18. In formulation development, why is solvent dielectric constant important for drug solubility?

  • It determines the color of the solution
  • It governs solvation energy and stabilization of ionic species
  • It controls melting point of the drug
  • It measures mechanical strength of the container

Correct Answer: It governs solvation energy and stabilization of ionic species

Q19. Which method is suitable for determining dielectric constant of thin films used in coatings?

  • Capacitance measurement using a parallel plate or interdigital electrodes
  • Flame photometry
  • Mass spectrometry
  • Optical microscopy

Correct Answer: Capacitance measurement using a parallel plate or interdigital electrodes

Q20. The real part of permittivity (ε’) represents:

  • Energy dissipation in the material
  • Energy storage capability in the material
  • Conductivity only
  • Magnetic susceptibility

Correct Answer: Energy storage capability in the material

Q21. Dielectric relaxation time τ is the characteristic time for:

  • Electronic transitions in UV range
  • Dipole reorientation under an alternating field
  • Crystal lattice melting
  • Evaporation of solvents

Correct Answer: Dipole reorientation under an alternating field

Q22. Which effect is commonly observed when salts are dissolved in polar solvents regarding dielectric properties?

  • Decrease in conductivity
  • Increase in dielectric loss and ionic conductivity
  • No change in dielectric behavior
  • Complete loss of dipolar relaxation

Correct Answer: Increase in dielectric loss and ionic conductivity

Q23. Which of the following is a practical application of dielectric measurements in tablet development?

  • Assessing tablet hardness by refractive index
  • Monitoring moisture content and binding effects during drying
  • Measuring pH of the tablet core directly
  • Determining API molecular weight

Correct Answer: Monitoring moisture content and binding effects during drying

Q24. The Cole–Cole plot is a graph of which quantities?

  • Imaginary conductivity vs temperature
  • Real permittivity (ε’) vs imaginary permittivity (ε”)
  • Capacitance vs resistance
  • Frequency vs wavelength

Correct Answer: Real permittivity (ε’) vs imaginary permittivity (ε”)

Q25. Which phenomenon indicates strong dipolar interactions and leads to broad dielectric relaxations?

  • Highly ordered crystalline structure without defects
  • Distribution of relaxation times due to heterogeneity
  • Pure electronic polarization only
  • Absence of hydrogen bonding

Correct Answer: Distribution of relaxation times due to heterogeneity

Q26. In dielectric measurements, why is electrode polarization a concern at low frequencies?

  • It enhances signal accuracy
  • It introduces spurious interfacial charges leading to artifacts
  • It reduces sample temperature
  • It only affects optical properties

Correct Answer: It introduces spurious interfacial charges leading to artifacts

Q27. Which of the following best describes the effect of increasing frequency on dipolar polarization?

  • Dipoles can follow the field more easily, increasing ε’
  • Dipoles cannot respond beyond a characteristic frequency, reducing ε’
  • Frequency has no effect on dipolar polarization
  • Dipolar polarization converts to electronic polarization

Correct Answer: Dipoles cannot respond beyond a characteristic frequency, reducing ε’

Q28. A dielectric constant value less than 1 would imply:

  • Material amplifies electric field (non-physical in passive media)
  • Typical behavior for most solvents
  • Very high polarity
  • Strong ionic conduction only

Correct Answer: Material amplifies electric field (non-physical in passive media)

Q29. Which parameter can dielectric spectroscopy directly monitor during a dissolution test of a tablet?

  • API chemical structure changes only
  • Changes in ionic mobility, hydration and release kinetics
  • Tablet weight with no relation to release
  • Only color changes of the medium

Correct Answer: Changes in ionic mobility, hydration and release kinetics

Q30. Which statement about dielectric constant and temperature for polar liquids is generally true?

  • Dielectric constant increases with increasing temperature
  • Dielectric constant is independent of temperature
  • Dielectric constant decreases with increasing temperature
  • Dielectric constant becomes infinite at high temperature

Correct Answer: Dielectric constant decreases with increasing temperature

Q31. Which relaxation model introduces a broadening parameter to account for symmetric broadening of relaxation peaks?

  • Debye model
  • Cole–Cole model
  • Cole–Davidson model
  • Arrhenius model

Correct Answer: Cole–Cole model

Q32. In practice, which sample condition must be controlled carefully during dielectric measurements of solutions?

  • Humidity, temperature, and electrode spacing
  • Only the sample color
  • The latitude of the lab
  • Magnetic field strength only

Correct Answer: Humidity, temperature, and electrode spacing

Q33. Relative permittivity εr and refractive index n are related at optical frequencies by which approximate relation (non-dispersive)?

  • εr ≈ n²
  • εr ≈ 1 / n
  • εr ≈ n / 2
  • εr and n are unrelated

Correct Answer: εr ≈ n²

Q34. Which of the following is NOT an application of dielectric constant data in pharmaceuticals?

  • Predicting solubility and miscibility
  • Monitoring freeze–thaw stability and crystallization
  • Directly sequencing DNA
  • Choosing suitable solvents for extraction

Correct Answer: Directly sequencing DNA

Q35. The imaginary part of permittivity ε” can originate from:

  • Only electronic polarization
  • Dipolar relaxation and ionic conduction losses
  • Only thermal expansion
  • None — ε” is always zero

Correct Answer: Dipolar relaxation and ionic conduction losses

Q36. A formulation scientist wants to reduce dielectric losses in a topical gel. Which approach is most relevant?

  • Increase ionic impurities and water content
  • Reduce ionic conductivity and bound water content
  • Add conductive salts to increase ε”
  • Increase temperature dramatically

Correct Answer: Reduce ionic conductivity and bound water content

Q37. Which of these describes the Cole–Davidson behavior?

  • Symmetric broadening of relaxation only
  • Asymmetric broadening with a high-frequency tail
  • No broadening, pure Debye behavior
  • Complete suppression of relaxation

Correct Answer: Asymmetric broadening with a high-frequency tail

Q38. Dielectric imaging or mapping in pharmaceutical tablets can reveal:

  • Distribution of API and moisture content non-uniformities
  • Only the tablet’s external color pattern
  • The atomic structure of API crystals
  • Exact chemical impurities by name

Correct Answer: Distribution of API and moisture content non-uniformities

Q39. Which is a typical frequency range for dielectric spectroscopy useful in studying molecular relaxations in formulations?

  • 10⁻⁶ to 10⁻³ Hz
  • Hz to GHz (10⁰ to 10⁹ Hz)
  • Only optical frequencies (10¹⁴ Hz)
  • Terahertz only

Correct Answer: Hz to GHz (10⁰ to 10⁹ Hz)

Q40. Which parameter would most likely increase the dielectric constant of a polymer matrix?

  • Incorporation of polar functional groups
  • Removal of all polar sites
  • Decreasing density without changing chemistry
  • Adding inert gas bubbles

Correct Answer: Incorporation of polar functional groups

Q41. When measuring εr of a liquid using a coaxial probe, a key advantage is:

  • Destructive sampling required
  • Fast, broadband measurements with minimal sample preparation
  • Only works for solids
  • Requires vacuum conditions

Correct Answer: Fast, broadband measurements with minimal sample preparation

Q42. How does hydrogen bonding affect dielectric properties of solvents?

  • It generally reduces dipole alignment and can lower ε’ or broaden relaxations
  • It always eliminates dielectric loss
  • It converts dipolar polarization to electronic polarization
  • It has no measurable effect

Correct Answer: It generally reduces dipole alignment and can lower ε’ or broaden relaxations

Q43. In the context of dielectric measurements, what is the role of calibration with reference liquids?

  • It is unnecessary for accurate results
  • To correct for probe geometry and systematic instrument errors
  • Only to determine sample color
  • To sterilize the probe

Correct Answer: To correct for probe geometry and systematic instrument errors

Q44. Which statement about dielectric constant and solute concentration is typically true for dilute solutions?

  • Dielectric constant remains exactly the same regardless of solute
  • Dielectric constant changes linearly with solute concentration for small concentrations
  • Dielectric constant increases exponentially with any solute
  • Dielectric constant becomes negative

Correct Answer: Dielectric constant changes linearly with solute concentration for small concentrations

Q45. The effective medium theory is used to:

  • Calculate optical spectra only
  • Estimate macroscopic dielectric properties of heterogeneous mixtures
  • Measure pH of solutions
  • Determine tensile strength of tablets

Correct Answer: Estimate macroscopic dielectric properties of heterogeneous mixtures

Q46. Which dielectric property is most sensitive to moisture uptake in powders?

  • Dielectric constant (ε’) and dielectric loss (ε”)
  • Magnetic permeability only
  • Thermal conductivity only
  • Optical absorbance only

Correct Answer: Dielectric constant (ε’) and dielectric loss (ε”)

Q47. Which is a limitation when using dielectric spectroscopy for formulation analysis?

  • It provides molecular-level structural information like NMR
  • Interpretation can be complicated by overlapping relaxations and ionic conduction
  • It cannot be used for liquids
  • It always gives exact concentration of API

Correct Answer: Interpretation can be complicated by overlapping relaxations and ionic conduction

Q48. Which of the following is true about frequency dispersion of ε’ in polar liquids?

  • ε’ increases indefinitely with frequency
  • ε’ decreases as frequency increases beyond molecular relaxation frequencies
  • ε’ is constant across all frequencies
  • ε’ becomes complex only at zero frequency

Correct Answer: ε’ decreases as frequency increases beyond molecular relaxation frequencies

Q49. In dielectric loss spectra, a Debye relaxation appears as:

  • A single symmetric peak in ε” vs log(frequency)
  • A linear increase with frequency
  • No features — flat baseline
  • Only noise

Correct Answer: A single symmetric peak in ε” vs log(frequency)

Q50. Why is knowledge of dielectric constant essential when selecting excipients for a lipid-based formulation?

  • It determines mechanical hardness of the excipient
  • It helps predict mixing, solubilization, and polarity matching between lipid and drug
  • Dielectric constant is irrelevant for lipid formulations
  • It only affects color and taste

Correct Answer: It helps predict mixing, solubilization, and polarity matching between lipid and drug

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