Final answer:
The most likely issue with the thermometer is that it is not reliable, failing to provide consistent and accurate readings of air temperature. Thermometers are valid instruments for measuring temperature, and proper use and placement are crucial for accuracy.
Step-by-step explanation:
The most likely problem with your new thermometer is that it is not reliable. Reliability in this context refers to the consistency of the measurements that the thermometer provides. If the thermometer's readings differ significantly from the weather reports (10 to 20 degrees above or below the reported temperature), it suggests that the instrument is not providing consistent and accurate measurements.
Thermometers are valid instruments for measuring air temperature, provided they are functioning correctly and are used under the right conditions. For instance, thermometers used in weather stations are shielded from the sunshine to avoid absorbing extra heat from the sun, which could result in inaccurate temperature readings. If your thermometer is exposed to direct sunlight or other heat sources, it may not measure the air temperature accurately.
Mercury or alcohol thermometers work based on the physical expansion or contraction of the liquid in response to temperature changes. If a thermometer is not functioning properly, it may be due to a fault in its design or because it has been damaged. It is important to ensure that the thermometer is placed in an optimal location for accurate temperature measurement, away from direct heat sources or reflective surfaces that could distort the reading.