Laboratory work: determining the relative humidity of air
A psychrometer consists of two identical thermometers: one shows the dry air temperature, the other, whose bulb is wrapped in damp gauze, shows the wet temperature. Water evaporates from the wet thermometer and the evaporation cools it, so it reads lower than the dry one. The drier the air, the faster the evaporation and the larger the temperature difference; if the air is saturated the difference is zero and φ = 100 %. Using both readings and their difference in a psychrometric table, we find φ. For example, with dry 24 °C and wet 19 °C the difference is 5 °C and the table gives φ ≈ 62 %. The work uses ordinary room thermometers without mercury and a table given by the teacher; do not touch fragments of a broken thermometer.
Do the work: record the dry and wet thermometer readings in the room, at an open window and in the bathroom (with an adult). Calculate the difference and find φ from the table. Compare the three places and say where the air is driest.