How is the barometric height of a simple barometer affected if
a). Its tube is pushed down into the trough of mercury?
b). Its tube is slightly tilted from vertical?
c). A drop of liquid is inserted inside the tube?

A). (a) remains unaffected (b) increases (c) decreases
B). (a) decreases (b) increases (c) decreases
C). (a) increases (b) remains unaffected (c) increases
D). (a) remains unaffected (b) remains unaffected (c) decreases

Hint: In this question the height of the mercury above the bowl in a barometer is a measure of the pressure of the air pushing on the mercury in the bowl. The mass of the mercury above the bowl times the force of gravity is equal to the pressure of air on the bowl.

Complete step-by-step solution:
a). Since the strong air pressure puts greater stress on the reservoir, forcing mercury in the column to higher. Low pressure allows mercury to drop to a lower column level by reducing the reservoir power. If the tube of a simple barometer is pushed down into the trough of mercury then the atmospheric force exerted on the tank will be adjusted by the mercury until the weight of the mercury column gets balanced. Hence the barometric height of a simple barometer remains unaffected.
b). When the tube is slightly tilted from vertical then the change in the atmospheric pressure will try to be balanced by the weight of the tube so the barometric height of a simple barometer remains unaffected.
c). A drop of liquid is inserted inside the tube then the vacuum will be replaced by that drop, then the drop will exert some pressure on the mercury and there will be a change in the barometer readings and a vacuum will be present inside the tube on top of the mercury. Hence we will get the decreased barometric height of a simple barometer.
Hence the option (D) is the correct answer.

Note: From the above discussion we can get some application of the above phenomenon as there is one easy way to measure air pressure and predict whether it will rain today or not. i.e. if the air pressure is rising and it's high then chances are it'll be a fine day, and if the pressure is falling, it's more likely to be wet, windy, and dull. Therefore the instrument used for measuring air pressure is called Barometers.