Here are 35 multiple-choice questions covering Heat, Temperature, and

Different Types of Thermometers, complete with detailed explanations for

each answer.

1. What is the fundamental difference between heat and

temperature?
a) Heat is energy; temperature is the measure of that energy.
b) Temperature is energy; heat is the measure of that energy.
c) Heat and temperature are the same.
d) Heat depends on mass; temperature does not.
Answer: (a)
Explanation: Heat is thermal energy transferred between systems due to a
temperature difference (measured in Joules). Temperature is a scalar
quantity that measures the average kinetic energy of particles in a
substance (measured in °C, K, or °F).

2. Which law states that heat flows spontaneously from a hotter to a

colder object?
a) Zeroth Law of Thermodynamics
b) First Law of Thermodynamics
c) Second Law of Thermodynamics
d) Third Law of Thermodynamics
Answer: (c)
Explanation: The Second Law of Thermodynamics dictates the direction of
heat flow—from higher to lower temperature—until thermal equilibrium is
reached.

3. At what temperature do Fahrenheit and Celsius scales read the

same value?
a) -40°
b) 0°
c) 32°
d) 100°
Answer: (a)
C5=F−3295C=9F−32 and
Explanation: Solving
setting C=FC=F gives C=−40C=−40.

4. Which thermometer uses the expansion of a liquid in a glass

tube?
a) Thermocouple
b) Bimetallic strip
c) Gas thermometer
d) Liquid-in-glass thermometer
Answer: (d)
Explanation: Liquid-in-glass thermometers (e.g., mercury or alcohol) rely on
thermal expansion of the liquid in a capillary tube.
5. Why is mercury preferred over alcohol in some thermometers?
a) Mercury is less toxic
b) Mercury has a higher boiling point
c) Alcohol expands more uniformly
d) Alcohol adheres to glass
Answer: (b)
Explanation: Mercury’s high boiling point (357°C) allows it to measure higher
temperatures than alcohol (boiling point ~78°C).

6. What principle does a bimetallic strip thermometer use?

a) Thermal conductivity
b) Differential expansion of metals
c) Electrical resistance change
d) Radiation emission
Answer: (b)
Explanation: Two bonded metals with different coefficients of thermal
expansion bend when heated, converting temperature to mechanical
displacement.

7. Which thermometer is best suited for measuring very high

temperatures (>1500°C)?
a) Platinum resistance thermometer
b) Thermocouple
c) Pyrometer
d) Gas thermometer
Answer: (c)
Explanation: Pyrometers measure temperature by detecting thermal
radiation (infrared/visible light) without physical contact, ideal for extreme
heat.

8. What is absolute zero?

a) 0°C
b) -273.15°F
c) 0 K
d) The melting point of ice
Answer: (c)
Explanation: Absolute zero (0 K or -273.15°C) is the theoretical temperature
where molecular kinetic energy is minimal.

9. Which law defines temperature via thermal equilibrium?

a) First Law
b) Second Law
c) Third Law
d) Zeroth Law
Answer: (d)
Explanation: The Zeroth Law states that if two systems are each in thermal
equilibrium with a third, they are in equilibrium with each other, defining
temperature.
10. A thermocouple generates voltage based on:
a) Seebeck effect
b) Peltier effect
c) Thomson effect
d) Joule heating
Answer: (a)
Explanation: The Seebeck effect produces a voltage when two dissimilar
metals at a junction experience a temperature gradient.

11. Why does a clinical thermometer have a constriction?

a) To prevent heat loss
b) To trap mercury after use
c) To increase sensitivity
d) To reduce expansion
Answer: (b)
Explanation: The constriction breaks the mercury thread when the
thermometer is removed, allowing the reading to remain until reset by
shaking.

12. Which property changes with temperature in a Resistance

Temperature Detector (RTD)?
a) Density
b) Electrical resistance
c) Volume
d) Thermal conductivity
Answer: (b)
Explanation: RTDs use metals (e.g., platinum) whose electrical resistance
increases predictably with temperature.

13. The triple point of water is:

a) 0°C
b) 100°C
c) 273.16 K
d) 373 K
Answer: (c)
Explanation: The triple point (273.16 K, 0.01°C) is where water coexists as
solid, liquid, and gas. It defines the Kelvin scale.

14. Linear expansion of a rod depends on:

a) Original length only
b) Temperature change only
c) Material and temperature change
d) Cross-sectional area
Answer: (c)
Explanation: ΔL=αL0ΔTΔL=αL0ΔT, where αα (material-dependent)
and ΔTΔT determine expansion.
15. Which thermometer responds fastest to temperature changes?
a) Mercury-in-glass
b) Bimetallic strip
c) Thermocouple
d) Gas thermometer
Answer: (c)
Explanation: Thermocouples have low thermal mass, enabling rapid response
(milliseconds).

16. A substance with low specific heat capacity:

a) Heats up slowly
b) Cools down slowly
c) Heats up quickly
d) Requires more energy to heat
Answer: (c)
Explanation: Specific heat capacity (cc) is energy required to raise 1 kg by 1
K. Low cc means less energy is needed for a temperature rise.

17. Invar is used in bimetallic strips because it has:

a) High thermal expansion
b) Low thermal expansion
c) High conductivity
d) Low density
Answer: (b)
Explanation: Invar (iron-nickel alloy) has near-zero thermal expansion,
making it ideal as the low-expansion component.

18. Which thermometer does NOT require physical contact?

a) RTD
b) Thermistor
c) Pyrometer
d) Thermocouple
Answer: (c)
Explanation: Pyrometers measure emitted radiation, enabling non-contact
temperature sensing.

19. The SI unit of temperature is:

a) Celsius
b) Fahrenheit
c) Kelvin
d) Rankine
Answer: (c)
Explanation: Kelvin (K) is the SI base unit for thermodynamic temperature.

20. A gas thermometer measures temperature using changes in:

a) Volume (constant pressure)
b) Pressure (constant volume)
c) Density
d) All of the above
Answer: (d)
Explanation: Gas thermometers use P∝TP∝T (constant V)
or V∝TV∝T (constant P), both relying on density changes.

21. Which material is commonly used in thermistors?

a) Copper
b) Platinum
c) Silicon
d) Metal oxides
Answer: (d)
Explanation: Thermistors are made from ceramic semiconductors (e.g., metal
oxides like Mn₂O₃), showing large resistance changes with temperature.

22. Heat transfer by convection occurs in:

a) Solids only
b) Fluids only
c) Vacuum
d) All matter
Answer: (b)
Explanation: Convection requires bulk fluid movement (liquids/gases), unlike
conduction (solids/fluids) or radiation (vacuum).
23. Why are bridges designed with expansion gaps?
a) To reduce weight
b) To allow thermal contraction
c) To prevent buckling from expansion
d) For aesthetic reasons
Answer: (c)
Explanation: Expansion gaps accommodate thermal expansion/contraction,
preventing structural damage.

24. Which thermometer is most accurate for laboratory use?

a) Mercury-in-glass
b) Thermocouple
c) Platinum RTD
d) Bimetallic strip
Answer: (c)
Explanation: Platinum RTDs offer high accuracy (±0.1°C), stability, and
linearity over wide ranges.

25. The Curie point is associated with:

a) Superconductivity
b) Thermal expansion
c) Loss of magnetism
d) Absolute zero
Answer: (c)
Explanation: The Curie point is the temperature above which ferromagnetic
materials lose spontaneous magnetization.

26. A blackbody radiator emits energy proportional to:

a) TT
b) T2T2
c) T3T3
d) T4T4

∝T4∝T4.
Answer: (d)
Explanation: Stefan-Boltzmann law: Radiant flux

27. Which liquid expands most uniformly?

a) Water
b) Mercury
c) Alcohol
d) Kerosene
Answer: (b)
Explanation: Mercury expands linearly over a wide range, making it reliable
for precise thermometry.

28. A thermistor has:

a) Positive temperature coefficient (PTC)
b) Negative temperature coefficient (NTC)
c) Zero temperature coefficient
d) Either (a) or (b)
Answer: (d)
Explanation: Most thermistors are NTC (resistance decreases with
temperature), but PTC types also exist.

29. The constant-volume gas thermometer is based on:

a) Boyle’s Law
b) Charles’s Law
c) Gay-Lussac’s Law
d) Avogadro’s Law
Answer: (c)
Explanation: Gay-Lussac’s Law states P∝TP∝T at constant volume.

30. Heat capacity depends on:

a) Mass only
b) Material only
c) Mass and material
d) Temperature only
Answer: (c)
Explanation: Heat capacity C=m×cC=m×c, where mm = mass and cc =
specific heat (material property).
31. Which phenomenon explains why railway tracks buckle in
summer?
a) Convection
b) Thermal expansion
c) Radiation
d) Specific heat
Answer: (b)
Explanation: Tracks expand when heated. If expansion joints are inadequate,
buckling occurs.

32. A pyrometer measures temperature by detecting:

a) Electrical resistance
b) Thermal expansion
c) Infrared radiation
d) Thermoelectric voltage
Answer: (c)
Explanation: Pyrometers sense infrared radiation emitted by hot objects.

33. At thermal equilibrium, two bodies have the same:

a) Heat
b) Internal energy
c) Temperature
d) Specific heat
Answer: (c)
Explanation: Thermal equilibrium implies no net heat flow, meaning identical
temperatures.

34. Which thermometer is suitable for a fever measurement?

a) Gas thermometer
b) Infrared ear thermometer
c) Thermocouple
d) Pyrometer
Answer: (b)
Explanation: Infrared ear thermometers provide quick, non-contact readings
ideal for medical use.

35. The coefficient of volume expansion (ββ) is approximately:

a) αα
b) 2α2α
c) 3α3α
d) α3α3
Answer: (c)
Explanation: For isotropic solids, β≈3αβ≈3α, where αα is the linear
expansion coefficient.

Bonus Questions:
 36. Why is water unsuitable for liquid-in-glass thermometers below
4°C?
a) It freezes
b) It expands non-linearly
c) It becomes less dense
d) It adheres to glass
Answer: (b)
Explanation: Water’s anomalous expansion (density decreases below 4°C)
makes it unpredictable for thermometry.

37. Which law underlies gas thermometer operation?

a) Newton’s Law
b) Ideal Gas Law
c) Fourier’s Law
d) Ohm’s Law
Answer: (b)
Explanation: The Ideal Gas Law (PV=nRTPV=nRT) links pressure, volume,
and temperature.

Key Concepts Covered:

 Heat vs. Temperature

 Thermal Expansion
 Thermometer Types (Liquid-in-glass, Bimetallic, Thermocouple, RTD,
Thermistor, Pyrometer)
 Temperature Scales (Celsius, Fahrenheit, Kelvin)
 Laws of Thermodynamics
 Specific Heat and Heat Capacity
 Applications (Clinical, Industrial, Laboratory)

Let me know if you'd like a PDF version or quizzes on specific subtopics!

Here are 25 multiple-choice questions on Humidity and Relative Humidity

with detailed explanations:

1. What is absolute humidity?

a) The ratio of water vapor mass to total air mass
b) The mass of water vapor per unit volume of air
c) The percentage of water vapor in air relative to saturation
d) The temperature at which air becomes saturated
Answer: (b)
Explanation: Absolute humidity is defined as the mass of water vapor (in
grams) per cubic meter of air (g/m³). It measures the actual quantity of water
vapor present, regardless of temperature.

2. Relative humidity depends on:

a) Air temperature only
b) Water vapor content only
c) Both air temperature and water vapor content
d) Atmospheric pressure only
Answer: (c)
Explanation: Relative humidity (RH) is the ratio of the current absolute
humidity to the maximum possible humidity at that temperature. If vapor
content stays constant, RH increases as temperature drops (and vice versa).

3. When air is saturated, its relative humidity is:

a) 0%
b) 50%
c) 75%
d) 100%
Answer: (d)
Explanation: Saturated air holds the maximum possible water vapor for its
temperature. At saturation, RH = 100%, and further vapor addition causes
condensation.

4. The dew point is:

a) The temperature at which relative humidity is 50%
b) The temperature at which air becomes saturated
c) The mass of dew formed overnight
d) A measure of absolute humidity
Answer: (b)
Explanation: Dew point is the temperature to which air must be cooled (at
constant pressure) to become saturated. At this point, condensation begins
(e.g., dew formation).
5. If air at 25°C has a dew point of 15°C, what happens when cooled
to 15°C?
a) Absolute humidity increases
b) Relative humidity decreases
c) Condensation begins
d) Evaporation accelerates
Answer: (c)
Explanation: Cooling air to its dew point (15°C) saturates it (RH = 100%).
Further cooling causes vapor to condense into liquid (e.g., dew, fog).

6. A psychrometer measures humidity using:

a) Human hair expansion
b) Electrical resistance change
c) Wet-bulb and dry-bulb temperatures
d) Infrared absorption
Answer: (c)
Explanation: A psychrometer uses two thermometers: a dry-bulb (measures
air temp) and a wet-bulb (cooled by evaporation). The temperature
difference indicates humidity.

7. Why does the wet-bulb temperature read lower than the dry-
bulb?
a) Evaporation absorbs heat
b) Condensation releases heat
c) Higher thermal conductivity
d) Instrument error
Answer: (a)
Explanation: Water evaporation from the wet-bulb wick absorbs latent heat,
lowering the temperature. The rate of cooling depends on air dryness.

8. In a hygrometer, human hair lengthens with:

a) Decreasing humidity
b) Increasing humidity
c) Increasing temperature
d) Decreasing pressure
Answer: (b)
Explanation: Hygroscopic materials like human hair expand when they
absorb moisture. Higher humidity causes hair to elongate, which is
mechanically measured.

9. If air temperature rises but absolute humidity remains constant,

relative humidity:
a) Increases
b) Decreases
c) Stays the same
d) Doubles
Answer: (b)
Explanation: Warmer air can hold more vapor. If vapor content stays fixed
but capacity increases, the saturation ratio (RH) decreases.
10. Relative humidity is typically highest:
a) At noon in summer
b) During rainy days
c) In deserts at night
d) Near industrial zones
Answer: (b)
Explanation: Rainy days have high vapor content and often cooler
temperatures, maximizing RH. Deserts have low RH despite temperature
drops due to minimal vapor.

11. The term "specific humidity" refers to:

a) RH expressed in g/m³
b) Mass of water vapor per mass of air
c) Volume of water vapor per air volume
d) Saturation vapor pressure
Answer: (b)
Explanation: Specific humidity is the ratio of water vapor mass to total air
mass (g/kg). Unlike RH, it is unaffected by temperature changes.

12. Condensation on a cold drink glass occurs because:

a) Absolute humidity decreases
b) Air near the glass cools below dew point
c) RH exceeds 200%
d) Glass releases stored water
Answer: (b)
Explanation: The cold glass chills adjacent air below its dew point, causing
vapor to condense onto the surface.

13. Which instrument uses lithium chloride to measure humidity?

a) Psychrometer
b) Hair hygrometer
c) Dew cell
d) Capacitive sensor
Answer: (c)
Explanation: A dew cell (hygrometer) uses lithium chloride solution. Its
electrical resistance changes with humidity absorption.

14. At 100% RH, the wet-bulb depression is:

a) 0°C
b) 5°C
c) 10°C
d) 15°C
Answer: (a)
Explanation: At saturation (100% RH), no evaporation occurs, so wet-bulb
and dry-bulb temperatures are equal → depression = 0°C.
15. Fog forms when:
a) RH < 50% and temperature rises
b) Air cools below dew point
c) Absolute humidity suddenly drops
d) Wind speed increases
Answer: (b)
Explanation: Fog is condensation of vapor into droplets when air cools to
saturation (dew point), typically overnight.

16. Which climate control issue occurs at low RH?

a) Mold growth
b) Static electricity
c) Corrosion
d) Reduced evaporation
Answer: (b)
Explanation: Low RH (<30%) allows static charge buildup (e.g., shocks,
electronics damage). High RH promotes mold/corrosion.

17. Vapor pressure deficit (VPD) is:

a) Saturation VP minus actual VP
b) Actual VP minus saturation VP
c) RH multiplied by VP
d) Dew point minus dry-bulb temp
Answer: (a)
Explanation: VPD = Saturation vapor pressure (max possible VP) – Actual
vapor pressure. It drives evaporation (e.g., plant transpiration).

18. Which equation relates saturation vapor pressure to

temperature?
a) Boyle’s Law
b) Clausius-Clapeyron Equation
c) Charles’s Law
d) Ideal Gas Law
Answer: (b)
Explanation: The Clausius-Clapeyron equation describes how saturation
vapor pressure increases exponentially with temperature.

19. In a closed container, adding water vapor without changing

temperature:
a) Increases absolute humidity but not RH
b) Increases RH until saturation
c) Decreases dew point
d) Has no effect
Answer: (b)
Explanation: In a closed space, vapor addition raises absolute humidity.
Since temperature is fixed, RH increases until reaching 100% (saturation).
20. Why does RH decrease when heating indoor air in winter?
a) Water vapor condenses
b) Absolute humidity decreases
c) Saturation vapor pressure increases
d) Air expands
Answer: (c)
Explanation: Heating raises air's saturation capacity. If vapor content
remains constant, RH drops even though absolute humidity is unchanged.

21. The most accurate primary hygrometer is:

a) Hair hygrometer
b) Capacitive sensor
c) Chilled mirror hygrometer
d) Psychrometer
Answer: (c)
Explanation: Chilled mirror hygrometers detect dew/frost formation on a
cooled mirror. They directly measure dew point and are used for calibration.

22. At constant temperature, doubling absolute humidity causes RH

to:
a) Halve
b) Double
c) Remain unchanged
d) Increase fourfold
Answer: (b)
Explanation: RH = (Absolute humidity / Saturation humidity) × 100%. At
fixed temperature, saturation humidity is constant, so doubling absolute
humidity doubles RH.

23. Which process increases atmospheric humidity?

a) Condensation
b) Evaporation
c) Freezing
d) Sublimation of ice
Answer: (b)
Explanation: Evaporation from surfaces (oceans, soil) adds vapor to air.
Condensation/sublimation reduce vapor content.

24. A "dry" feeling at 30% RH vs. "damp" at 80% is due to:

a) Differences in absolute humidity
b) Skin evaporation rate
c) Air density
d) Thermal conductivity
Answer: (b)
Explanation: Low RH accelerates sweat evaporation, causing "dryness." High
RH slows evaporation, creating a "damp" sensation.
 25. Industrial applications requiring low RH include:
a) Textile manufacturing
b) Pharmaceutical storage
c) Greenhouses
d) Paper drying
Answer: (b)
Explanation: Pharmaceuticals, electronics, and archives require low RH (~30-
40%) to prevent degradation, mold, or corrosion.

Key Concepts Covered:

 Definitions: Absolute humidity, relative humidity, specific humidity, dew

point
 Instruments: Psychrometer, hygrometer, chilled mirror, dew cell
 Principles: Evaporation cooling, saturation, condensation
 Calculations: RH vs. temperature, vapor pressure deficit
 Applications: Weather prediction, climate control, industrial processes

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