Effect of temperature on viscosity MCQs With Answer is a focused revision tool designed for B. Pharm students to master how temperature alters fluid flow and formulation behavior. This introduction covers key concepts—temperature dependence of liquid and gas viscosities, Arrhenius/Andrade relationships, activation energy of flow, Newtonian vs non‑Newtonian response, viscometry methods and practical formulation implications such as dissolution, stability, syringeability and rheology of polymers and suspensions. Clear, exam‑oriented MCQs reinforce critical calculations, units (cP, St), and regulatory measurement practices. Use these questions to strengthen understanding of how temperature control and excipient choice affect drug performance. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. Which general trend describes how viscosity of most liquids changes with increasing temperature?
- Viscosity increases with temperature
- Viscosity decreases with temperature
- Viscosity remains constant with temperature
- Viscosity first increases then decreases
Correct Answer: Viscosity decreases with temperature
Q2. How does viscosity of gases typically change with increasing temperature?
- Viscosity decreases because intermolecular forces weaken
- Viscosity increases because molecular momentum transfer increases
- Viscosity remains unchanged
- Viscosity fluctuates unpredictably
Correct Answer: Viscosity increases because molecular momentum transfer increases
Q3. Which equation commonly models the temperature dependence of liquid viscosity in an Arrhenius-like form?
- η = A + BT
- η = A exp(B/T)
- η = A/T + B
- η = AT^2
Correct Answer: η = A exp(B/T)
Q4. In Andrade’s equation ln η = ln A + B/T, what does B represent conceptually?
- Density of the liquid
- Activation energy related parameter for flow
- Shear rate
- Viscosity index
Correct Answer: Activation energy related parameter for flow
Q5. What are the SI units for dynamic (absolute) viscosity?
- Pascal-second (Pa·s)
- Newton per meter (N/m)
- Centistoke (cSt)
- Pascal per meter (Pa/m)
Correct Answer: Pascal-second (Pa·s)
Q6. Which unit is commonly used in pharmacy for viscosity and equals 0.001 Pa·s?
- Poise (P)
- Centipoise (cP)
- Stokes (St)
- Centistoke (cSt)
Correct Answer: Centipoise (cP)
Q7. Kinematic viscosity differs from dynamic viscosity by including which fluid property?
- Temperature
- Pressure
- Density
- Surface tension
Correct Answer: Density
Q8. The relationship between kinematic viscosity (ν), dynamic viscosity (μ) and density (ρ) is:
- ν = μ × ρ
- ν = μ / ρ
- μ = ν / ρ
- μ = ν × ρ^2
Correct Answer: ν = μ / ρ
Q9. Which viscometer is based on flow through a calibrated capillary tube under gravity?
- Brookfield rotational viscometer
- Ostwald (capillary) viscometer
- Falling-ball viscometer
- Vibrational viscometer
Correct Answer: Ostwald (capillary) viscometer
Q10. For a Newtonian liquid, how does viscosity change with applied shear rate?
- Viscosity decreases with shear rate
- Viscosity increases with shear rate
- Viscosity remains constant regardless of shear rate
- Viscosity oscillates with shear rate
Correct Answer: Viscosity remains constant regardless of shear rate
Q11. Which rheological behavior describes shear-thinning fluids often used in topical formulations?
- Dilatant
- Pseudoplastic
- Newtonian
- Bingham plastic
Correct Answer: Pseudoplastic
Q12. A suspension that becomes less viscous with time under constant shear exhibits which property?
- Rheopectic
- Thixotropic
- Dilatant
- Pseudoelastic
Correct Answer: Thixotropic
Q13. Which expression correctly relates viscosity to temperature in Arrhenius form?
- η = A exp(E/RT)
- η = A ln(T/E)
- η = A/T^E
- η = A + E*T
Correct Answer: η = A exp(E/RT)
Q14. In the Arrhenius equation for viscosity, what does E represent?
- Electric charge
- Activation energy of viscous flow
- Emulsification index
- Elastic modulus
Correct Answer: Activation energy of viscous flow
Q15. Which factor typically increases the activation energy of viscous flow in polymer solutions?
- Lower molecular weight polymer
- Higher polymer‑solvent interactions and entanglement
- Decreasing polymer concentration
- Increasing temperature only
Correct Answer: Higher polymer‑solvent interactions and entanglement
Q16. The viscosity index (VI) is a measure used for lubricants; a higher VI indicates what?
- Greater sensitivity to temperature
- Less change in viscosity with temperature
- Higher viscosity at all temperatures
- Lower viscosity at all temperatures
Correct Answer: Less change in viscosity with temperature
Q17. Which relation links diffusion coefficient (D) to viscosity (η) and particle radius (r)?
- Stokes–Einstein: D = kT/(6π η r)
- Fick’s law: D = η/kT
- Arrhenius: D = A exp(E/RT)
- Poiseuille: D = π r^4
Correct Answer: Stokes–Einstein: D = kT/(6π η r)
Q18. How does increasing viscosity generally affect drug diffusion and dissolution rate?
- Increases diffusion and accelerates dissolution
- Has no effect on diffusion or dissolution
- Decreases diffusion and slows dissolution
- Only affects dissolution but not diffusion
Correct Answer: Decreases diffusion and slows dissolution
Q19. Which excipient class is commonly used as a viscosity enhancer in oral suspensions?
- Sugars
- Semi-synthetic cellulose derivatives (e.g., CMC, HPMC)
- Preservatives
- Surfactants only
Correct Answer: Semi-synthetic cellulose derivatives (e.g., CMC, HPMC)
Q20. For quality control, why must temperature be controlled when measuring viscosity?
- Viscosity is independent of temperature so control is unnecessary
- Viscosity varies strongly with temperature and affects reproducibility
- Temperature only affects density, not viscosity
- To prevent chemical reactions during measurement
Correct Answer: Viscosity varies strongly with temperature and affects reproducibility
Q21. Which instrument measures torque required to rotate a spindle in a fluid to determine viscosity?
- Ostwald viscometer
- Brookfield rotational viscometer
- Capillary electrophoresis
- Freeze dryer
Correct Answer: Brookfield rotational viscometer
Q22. If a liquid’s viscosity at 20°C is 100 cP and at 40°C is 25 cP, what general conclusion can be drawn?
- Viscosity increased with temperature
- Viscosity decreased significantly with temperature
- Viscosity remained unchanged
- Measurement error occurred
Correct Answer: Viscosity decreased significantly with temperature
Q23. Which of the following is NOT a reason temperature affects viscosity?
- Changes in molecular mobility
- Alteration of intermolecular forces
- Change in solvent polarity only
- Thermal expansion affecting density
Correct Answer: Change in solvent polarity only
Q24. Which flow behavior is typical of concentrated cornstarch in water?
- Pseudoplastic (shear-thinning)
- Dilatant (shear-thickening)
- Newtonian
- Bingham plastic
Correct Answer: Dilatant (shear-thickening)
Q25. Which statement describes a Bingham plastic?
- No yield stress and linear flow from zero shear
- Requires a finite yield stress before flow begins
- Viscosity decreases exponentially with temperature
- Only occurs in dilute solutions
Correct Answer: Requires a finite yield stress before flow begins
Q26. In pharmaceutics, why is viscosity important for topical formulations?
- Only for color stability
- Affects spreadability, retention time and drug release
- Determines melting point
- Has no practical significance
Correct Answer: Affects spreadability, retention time and drug release
Q27. Which factor generally causes viscosity to increase in polymer solutions?
- Decreasing polymer concentration
- Lowering molecular weight
- Increasing polymer molecular weight and entanglement
- Raising temperature alone always
Correct Answer: Increasing polymer molecular weight and entanglement
Q28. Which viscosity behavior improves syringeability of a parenteral formulation?
- Very high viscosity at injection temperature
- High viscosity at low temperature but low at body temperature
- Shear-thickening at syringe shear rates
- Extremely thixotropic requiring long rest
Correct Answer: High viscosity at low temperature but low at body temperature
Q29. Which temperature control practice is essential when comparing viscosity data across labs?
- Ignorе temperature differences because viscosity is constant
- Report temperature and measure at the same reference temperature
- Measure only at room temperature without recording it
- Vary temperature during measurement
Correct Answer: Report temperature and measure at the same reference temperature
Q30. How does adding dissolved salts typically affect viscosity of aqueous solutions?
- Always decreases viscosity
- Can increase or decrease depending on ion‑solvent interactions
- Has no effect on viscosity
- Instantly makes solution Newtonian
Correct Answer: Can increase or decrease depending on ion‑solvent interactions
Q31. Which phenomenon explains why liquid viscosity often shows an exponential decline with temperature?
- Linear thermal expansion only
- Activation energy barrier for molecular rearrangement is overcome more easily
- Increased surface tension
- Decrease in molecular weight
Correct Answer: Activation energy barrier for molecular rearrangement is overcome more easily
Q32. The glass transition temperature (Tg) is most relevant to viscosity behavior of which materials?
- Simple inorganic salts in water
- Amorphous polymers and glasses
- Gaseous drugs
- Pure crystalline metals
Correct Answer: Amorphous polymers and glasses
Q33. Which method is suitable for measuring very low viscosities (e.g., mobile solvents)?
- Capillary (Ostwald) viscometer
- Brookfield with large spindle only
- Penetrometer
- Thermogravimetric analyzer
Correct Answer: Capillary (Ostwald) viscometer
Q34. For non-Newtonian fluids, which parameter must be specified along with viscosity?
- Temperature only
- Shear rate or shear stress conditions
- Color of the formulation
- Packaging material
Correct Answer: Shear rate or shear stress conditions
Q35. Which temperature range is commonly used for many pharmaceutical viscosity measurements?
- -40 to -20°C
- 0 to 100°C without specification
- 25°C (room temp) and 37°C (physiological) standardized
- Only at boiling point
Correct Answer: 25°C (room temp) and 37°C (physiological) standardized
Q36. What is the likely effect on an emulsion’s viscosity when temperature increases near the melting point of a fatty phase?
- Viscosity increases due to solidification
- Viscosity decreases due to melting and reduced internal structure
- No change
- Emulsion becomes gaseous
Correct Answer: Viscosity decreases due to melting and reduced internal structure
Q37. Which polymeric thickener exhibits strong temperature‑dependent viscosity in aqueous systems?
- Hydroxypropyl methylcellulose (HPMC)
- Sodium chloride
- Methanol
- Hydrogen gas
Correct Answer: Hydroxypropyl methylcellulose (HPMC)
Q38. When plotting ln η versus 1/T (Kelvin), a straight line suggests which model is applicable?
- Newtonian constant model
- Arrhenius/Andrade-type temperature dependence
- Power-law with no temperature dependence
- Log-normal viscosity distribution
Correct Answer: Arrhenius/Andrade-type temperature dependence
Q39. In emulsion stability, why might low-temperature storage increase apparent viscosity?
- Because thermal motion increases
- Because the dispersed phase may solidify or coarsen, increasing structure
- Because viscosity is independent of phase state
- Because surfactant activity always decreases
Correct Answer: Because the dispersed phase may solidify or coarsen, increasing structure
Q40. Which statement about calibrating viscometers is correct?
- Calibration is unnecessary if using the same instrument
- Calibration with standard fluids and temperature control ensures accurate results
- Only viscosity index calibration is required
- Calibration only matters for gases
Correct Answer: Calibration with standard fluids and temperature control ensures accurate results
Q41. Which of the following decreases the temperature sensitivity of a formulation’s viscosity?
- Using a single low molecular weight polymer
- Adding a mix of thickeners that provide shear stability
- Eliminating all excipients
- Storing always at freezing temperature
Correct Answer: Adding a mix of thickeners that provide shear stability
Q42. Which is true about viscosity of ionic liquids with temperature?
- Ionic liquids always increase viscosity with temperature
- Ionic liquids typically decrease viscosity with increasing temperature, like other liquids
- Ionic liquids have no measurable viscosity
- Their viscosity is independent of molecular interactions
Correct Answer: Ionic liquids typically decrease viscosity with increasing temperature, like other liquids
Q43. What effect does temperature have on shear-thinning polymer gels?
- Higher temperature always makes them shear-thickening
- Higher temperature can reduce viscosity and modify network strength, affecting shear response
- Temperature does not affect polymer gels
- They evaporate immediately
Correct Answer: Higher temperature can reduce viscosity and modify network strength, affecting shear response
Q44. Which property of oils is often characterized by measuring viscosity at different temperatures?
- Melting point only
- Viscosity index and temperature susceptibility
- Color stability
- Electrical conductivity
Correct Answer: Viscosity index and temperature susceptibility
Q45. In viscometric analysis, why are reference fluids like silicone oils used?
- They are inert and have certified viscosities over temperature ranges for calibration
- They react with samples to show trends
- They are cheaper than water
- They change color with temperature
Correct Answer: They are inert and have certified viscosities over temperature ranges for calibration
Q46. A pharmaceutical gel shows significantly lower viscosity at 37°C than at 25°C. How might this influence drug delivery when applied to skin?
- Less spreadability and slower drug release
- Greater spreadability and potentially faster drug release
- No effect on delivery
- Will make the drug inactive
Correct Answer: Greater spreadability and potentially faster drug release
Q47. Which temperature-dependent behavior is critical for spray formulations and aerosols?
- Viscosity determines spray droplet formation and atomization efficiency
- Temperature only affects bottle color
- Viscosity is irrelevant for sprays
- Only vapor pressure matters
Correct Answer: Viscosity determines spray droplet formation and atomization efficiency
Q48. When assessing stability, why monitor viscosity as a function of temperature cycling?
- To ensure packaging aesthetics
- To detect irreversible structural changes like aggregation, gelling or phase separation
- Viscosity cycling is only for research and not stability
- To measure pH indirectly
Correct Answer: To detect irreversible structural changes like aggregation, gelling or phase separation
Q49. Which mathematical transform allows linearization for determining activation energy from viscosity vs temperature data?
- Plot η vs T directly
- Plot ln η vs 1/T (Arrhenius plot)
- Plot η^2 vs T
- Plot 1/η vs ln T
Correct Answer: Plot ln η vs 1/T (Arrhenius plot)
Q50. For a formulation intended for cold climates, what viscosity property is desirable?
- Strong increase in viscosity at low temperature causing poor flow
- Stable viscosity across a wide temperature range to maintain performance
- Very low viscosity at all temperatures
- Viscosity highest at body temperature only
Correct Answer: Stable viscosity across a wide temperature range to maintain performance
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