Interpreting wet-bulb temperature: A low measured wet-bulb temperature generally indicates very __________ relative humidity.

Introduction / Context:
Wet-bulb temperature (WBT) reflects the combined effect of temperature and humidity through evaporative cooling. It is vital for assessing comfort, cooling tower performance, and evaporative cooler effectiveness.

Given Data / Assumptions:

• Psychrometric relationships at standard atmospheric pressure.
• WBT is measured with a wetted wick over a thermometer bulb in moving air.

Concept / Approach:
When air is dry (low RH), evaporation from the wet wick is strong, causing a large temperature drop between dry-bulb temperature (DBT) and WBT. Thus, a low WBT relative to DBT signals low humidity. Conversely, at high RH, evaporation is limited and WBT approaches DBT.

Step-by-Step Solution:
Compare DBT and WBT: a large DBT−WBT gap means strong evaporative potential → dry air.If WBT nearly equals DBT, air is near saturation → high humidity.Therefore, a low WBT reading (relative to DBT) indicates low RH.

Verification / Alternative check:
Use the sling psychrometer: compute RH via tables from DBT and WBT; large depression corresponds to low RH values.

Why Other Options Are Wrong:

• High or fixed RH values contradict psychrometric tables; pressure effects are minor at normal altitudes for this qualitative inference.

Common Pitfalls:
Interpreting absolute WBT without reference to DBT; always consider the depression (DBT−WBT).

Final Answer:
low