Hygrometer Practice Questions
20 free Hygrometer practice questions for the General Science. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
What is the primary function of a hygrometer?
- A To measure the pressure of the atmosphere
- B To measure the relative density of a liquid sample
- C To measure the moisture content of the air
- D To measure the purity of milk samples
Correct answer: To measure the moisture content of the air
A hygrometer is a scientific instrument used to measure humidity, which is the amount of water vapor present in the air or other gases. It is a critical tool in meteorology, manufacturing, and HVAC systems.
A psychrometer is a specific type of hygrometer that utilizes which two components?
- A A dry-bulb and a wet-bulb thermometer
- B A mercury bulb and an alcohol bulb
- C A bimetallic strip and a spring
- D An infrared sensor and a laser emitter
Correct answer: A dry-bulb and a wet-bulb thermometer
A psychrometer measures relative humidity by comparing the readings of a standard dry-bulb thermometer and a wet-bulb thermometer covered in a moistened wick. The difference in temperature caused by evaporation (evaporative cooling) is used to calculate humidity.
In a hair hygrometer, what happens to the human or animal hair as the humidity increases?
- A The hair becomes longer.
- B The hair becomes shorter.
- C The hair changes color.
- D The hair becomes more brittle.
Correct answer: The hair becomes longer.
Hair is naturally hygroscopic, meaning it absorbs moisture from the air. As humidity increases, the hair strand expands and lengthens, which is mechanically translated to a pointer on a dial.
Which type of hygrometer measures the temperature at which water vapor begins to condense on a polished metal surface?
- A Chilled mirror dew point hygrometer
- B Electrical resistance-type hygrometer
- C Polymer film capacitive hygrometer
- D Thermal conductivity hygrometer
Correct answer: Chilled mirror dew point hygrometer
A chilled mirror hygrometer cools a reflective surface until dew forms. By detecting the exact temperature where condensation occurs, the instrument provides a highly accurate measurement of the dew point.
If the dry-bulb and wet-bulb temperatures in a psychrometer are identical, what does this indicate about the relative humidity?
- A The humidity is 0%.
- B The humidity is 50%.
- C The humidity is 100%.
- D The humidity is below 20%.
Correct answer: The humidity is 100%.
When the air is fully saturated with moisture (100% relative humidity), no evaporation can occur from the wet bulb. Consequently, no evaporative cooling takes place, and both thermometers will show the same temperature.
Which of the following materials is commonly used in electronic 'capacitive' hygrometers?
- A A polymer or metal oxide thin film
- B A concentrated lithium chloride solution
- C A piece of treated human hair
- D A column of liquid mercury
Correct answer: A polymer or metal oxide thin film
Capacitive hygrometers use a thin strip of polymer or metal oxide that changes its electrical capacitance based on the amount of moisture it absorbs. This change is then converted into a digital humidity reading.
The 'dew point' is best defined as:
- A The temperature at which water boils.
- B The maximum amount of water air can hold at any temperature.
- C The temperature at which air becomes saturated with water vapor.
- D The ratio of actual water vapor to the maximum possible water vapor.
Correct answer: The temperature at which air becomes saturated with water vapor.
The dew point is a physical constant for a given parcel of air. It represents the temperature to which air must be cooled at constant pressure for water vapor to condense into liquid water.
Which type of hygrometer is most likely to be used in a remote weather station due to its small size and lack of moving parts?
- A Whirling sling psychrometer
- B Mechanical hair hygrometer
- C Digital capacitive hygrometer
- D Chemical absorption hygrometer
Correct answer: Digital capacitive hygrometer
A digital capacitive hygrometer is compact, has no moving parts to wear out, and produces an electrical signal that a data logger can record. That makes it well suited to an unattended remote weather station.
How does a 'sling psychrometer' accelerate the process of obtaining a reading?
- A By heating the air around the thermometers.
- B By using an electric fan to blow air over the bulbs.
- C By whirling the thermometers to speed evaporation.
- D By using a chemical desiccant to dry the air.
Correct answer: By whirling the thermometers to speed evaporation.
A sling psychrometer is attached to a handle and spun in a circle. This movement ensures a steady flow of air over the wet bulb, maximizing the rate of evaporation to reach the stable wet-bulb temperature quickly.
What is 'absolute humidity'?
- A The mass of water vapor per unit volume of air.
- B The percentage of saturation at a given temperature.
- C The temperature at which frost forms.
- D The pressure exerted by water vapor alone.
Correct answer: The mass of water vapor per unit volume of air.
Absolute humidity is a measure of the actual amount of water vapor in the air, regardless of temperature. It is typically expressed in grams per cubic meter (g/m³).
Which scientific instrument is often paired with a hygrometer in a 'hygrothermograph'?
- A Aneroid barometer
- B Anemometer
- C Thermometer
- D Rain gauge
Correct answer: Thermometer
A hygrothermograph is a recording instrument that tracks both humidity and temperature over time. It typically uses a rotating drum and pens to create a continuous visual record of both variables.
The use of a hygrometer is vital in museums and archives primarily to prevent:
- A The accumulation of dust and grime on artifact surfaces.
- B Fluctuations in air pressure that crack glass cases.
- C Mold growth and the degradation of organic materials.
- D The loss of color due to ultraviolet light.
Correct answer: Mold growth and the degradation of organic materials.
High humidity promotes the growth of mold and mildew, while very low humidity can cause wood and paper to become brittle. Precise humidity control, monitored by hygrometers, is essential for preserving historical items.
Which of these factors can lead to an error in a psychrometer reading?
- A Using distilled water on the wick.
- B High air speed over the bulbs.
- C Touching the wet-bulb wick with oily fingers.
- D Positioning the instrument in the shade during readings.
Correct answer: Touching the wet-bulb wick with oily fingers.
Oils from the skin can contaminate the wick and inhibit its ability to absorb water through capillary action. This leads to reduced evaporation and an inaccurately high wet-bulb reading.
What happens to the 'Relative Humidity' of a sealed room if the temperature increases but the amount of water vapor stays the same?
- A It increases.
- B It decreases.
- C It remains constant.
- D It drops to zero.
Correct answer: It decreases.
Relative humidity is temperature-dependent because warm air can hold more water vapor than cold air. If the air gets warmer but the water content is constant, the air is 'further' from saturation, resulting in a lower percentage.
A 'gravimetric hygrometer' is considered the most accurate type because it involves:
- A Measuring the change in the weight of a drying agent.
- B Using a laser to count water molecules.
- C Calculating the weight of the air column above the sensor.
- D Measuring the pull of gravity on water vapor.
Correct answer: Measuring the change in the weight of a drying agent.
Gravimetric hygrometry is a primary standard method where a known volume of air is passed through a desiccant. The moisture is weighed directly, providing an absolute and highly precise measurement.
Why is 'Relative Humidity' expressed as a percentage?
- A Because it is a ratio of actual to saturation vapor pressure.
- B Because it gives the chance of rainfall in the coming hour.
- C Because it counts the grams of vapor in a kilogram of dry air.
- D Because its scale was fixed by international agreement.
Correct answer: Because it is a ratio of actual to saturation vapor pressure.
Relative humidity compares how much water vapor is currently in the air to the maximum amount the air could hold at that specific temperature. A value of 100% means the air is fully saturated.
In meteorology, what is the term for the lines on a weather map connecting points of equal humidity?
- A Isobars
- B Isotherms
- C Isohumes
- D Isohyets
Correct answer: Isohumes
While isobars connect equal pressure and isotherms connect equal temperature, isohumes are the lines used to show areas of equal relative humidity.
How does a thermal conductivity hygrometer determine humidity?
- A By tracking how far a strand of treated human hair stretches.
- B By comparing heat loss from a sensor in dry and sample air.
- C By drying the sample with a heating element and weighing it.
- D By timing how long a chilled mirror takes to fog.
Correct answer: By comparing heat loss from a sensor in dry and sample air.
Thermal conductivity hygrometers compare the heat loss from two identical sensors, one in dry air and one in the sample air. Since water vapor affects the thermal conductivity of air, the difference reveals the humidity level.
When using a psychrometer, the 'wet-bulb depression' refers to:
- A The drop in pressure near the instrument.
- B The lowest temperature the wet bulb can reach in perfectly still air.
- C The difference between the dry-bulb and wet-bulb temperatures.
- D The amount of water the wick absorbs each minute.
Correct answer: The difference between the dry-bulb and wet-bulb temperatures.
The wet-bulb depression is the numerical difference between the two thermometer readings. A larger depression indicates drier air, as more evaporation occurred to cool the wet bulb.
Which of the following describes 'specific humidity'?
- A The mass of water vapor per unit mass of moist air.
- B The mass of water vapor per unit mass of dry air.
- C The mass of water vapor contained in one cubic meter of air.
- D The share of the air's saturation capacity currently in use.
Correct answer: The mass of water vapor per unit mass of moist air.
Specific humidity is a ratio used in thermodynamics and meteorology. It measures the mass of water vapor divided by the total mass of the air (vapor plus dry air), usually expressed in grams per kilogram (g/kg).