General Knowledge - Physics - Discussion

I think option A is correct because mercury can detect small change in temperature but water can't. Only the visibility can't be the reason for the use of mercury.

I think the answer should be C ie mercury have comparably small specific heat capacity. Means in lower temperature also it ll show its level. Mg specific heat is 140J/kg/k water has 4180J/kg/k. If visibility is matter then we add any color substance to water and then we can use water. But is not right. The answer should be changed to C.

I don't agree then why it is not used in digital thermometer?

Mercury is used in thermometers as opposed to water because of a few simple reasons.

1. While mercury is a liquid, it is doesn't have the same properties as water, therefore it won't condensate at the top of the thermometer, making the reading of temperature more accurate.

2. It relies on thermal expansion meaning the molecular bonds will expand with heat and contract with cold. This is why the mercury fluctuates according to temperature.

3. It's melting point is -38.83°C (water is only 0 °C) and doesn't boil until 356.73 °C (water boils at 100 °C) which made mercury a better candidate to read temperature since it's liquid stage goes a lot farther than water.

4. Mercury's silver appearance, makes it easy to read temperatures at just a glance.

Mercury is still used in some thermometers but because of its toxicity levels, it is gradually being replaced by alcohol or electronic thermometers.

I agree with what Sourajit said, the long height resulting due to the density of water being lower than that of mercury would be unmanageable, so the answer to this question should be changed, its not because of visibility factor.

If water were used instead of mercury, the height of the column required would be very large. The density of mercury being much more than that of water, it expands lesser and thus can be used in manageable tubes. There is nothing limiting us from using water instead of mercury except the height of the tube.