In an experiment to measure the specific heat capacity of water I'm trying to make it as accurate as possible. And somewhere I read that a sensitive thermometer absorbs little heat. By "sensitive" I am referring to the amount of change in thermometric property for a unit change in temperature.
A thermometer is "sensitive" when it absorbs as little heat as possible from the item it is trying to measure. Any heat absorbed by the thermometer will lower the temperature of the item, and hence cause a false reading.
This problem occurs whenever you are trying to measure anything. Your measuring device should always aim for the smallest possible disturbance of its environment, as any disturbance will affect the measurement. For example, a voltmeter should draw as little current as possible, to avoid changing the measured voltage; an ideal ammeter has zero resistance, to avoid changing the measured current.
A thermometer that absorbs a lot of heat will change the temperature of what it is measuring and then measure the wrong temperature.
To be sensitive, any sensor must disturb its enivronment in a very predictable way. For a thermometer that is easiest to achieve for one that minimizes heat absorption.
The sensitivity of a thermometer is defined as the smallest temperature change which can be measured, thus if you have two mercury in glass thermometers and the only difference between them is the size of the bulb, the one with the larger bulb will be more sensitive.
The thermometer with the smaller bulb will react faster to temperature changes and affects the temperature readings less as it has a smaller thermal capacity.
It appears that in the answer given (and hence the question) the word sensitive has been used incorrectly and the question should have been in terms of the thermal capacity of the thermometer.
