If a thermometer bulb is not completely immersed in water, what effect will this have on the measured melting point? Will it be higher or lower than actual?
The measured melting point probably will be lower than it should be because not all of the mercury in the bulb is subject to expansion/contraction due to the temperature of the liquid. As you have described the post you are measuring the temperature of the water.
If a thermometer bulb is not completely immersed in water, it will have an effect on the measured melting point. Specifically, the measured melting point will be higher than the actual melting point.
To understand why this happens, it's important to know how a thermometer works. A typical thermometer consists of a bulb containing a temperature-sensitive liquid, such as mercury or alcohol. As the temperature changes, the liquid expands or contracts, and this expansion or contraction is measured on a scale.
When measuring the melting point of a substance, the thermometer bulb is typically placed inside a container filled with the substance being tested. The substance is heated until it starts to melt, and the temperature at which this occurs is noted as the melting point.
If the thermometer bulb is not completely immersed in the substance being tested, the temperature detected by the thermometer will not accurately reflect the true temperature of the substance. The portion of the bulb that is exposed to the air will be affected by the cooler air temperature, leading to a higher reading on the thermometer.
This happens due to the phenomenon of conduction. The heat energy from the substance being tested is not efficiently transferred to the thermometer bulb because the air serves as a barrier. As a result, the temperature reading will be slightly higher than the actual melting point.
To obtain a more accurate measurement, it is crucial to ensure that the thermometer bulb is fully immersed in the substance being tested. This promotes better heat transfer and allows for a more precise measurement of the melting point.