Temperature measurement using thermometer
I have two samples of water – 'A' and 'B'. My thermometer measured them to be 90 °C. They both have different volumes. So, the kinetic energy of the particles of sample A and B is same or different?


The total kinetic energy is different. The average kinetic energy per particle is the same.


  Through this question, I want to ask whether temperature measurement results depend upon how many particles hit the bulb of my thermometer or it is independent of this? 


In your specific example, the same number of particles hit the bulb because it just depends on the area of the bulb, as long as it is covered in water. Not only is water hitting the bulb, the atoms in the bulb are also hitting the water. After they have done this for a while, water and bulb are at the same temperature.


  If it is independent of this, then how thermometer works? As another example, let me consider a gas which has the density of 2 mol/22.4 L. Its temperature recorded by my thermometer is 60 °C. Then its density is reduced to about 10 atoms/22.4 litre. Now, its temperature is the same?


For the example with the two gases at the same temperature but at different pressure (i.e. particle density), the situation is a bit different, but the thermometer still works. There are a different number of "hits" in this case, but if you wait long enough, the gas and the bulb will be at the same temperature.


  Please provide me the simplest answer as I am in class 9 only.


I tried, but if the question addresses a complicated phenomenon, the answer can't be super-simple.


  [From the comments:] So, if i have 10,000000 particles in 1 L and 10 particles in 1L, temperature is going to be same or different?? (I mean the readings)


Ideally, there should be more sample than thermometer. This means that no matter what the temperature of the thermometer was to start, it will have the temperature of the sample afterwards. With only 10 particles in the sample, the 10 particles will take on the temperature of the thermometer (and the enclosure), so you will be unable to measure the initial temperature of the sample.


  [My own question] If the sample keeps hitting the thermometer, why doesn't it get hotter and hotter?


As I said above, the thermometer also keeps hitting the sample. There is some net transfer of energy while the temperatures are different (from hot to cold, warming up the colder and cooling down the hotter). Once the temperatures are the same, sample and thermometer keep "hitting each other", but the temperature of both stays constant (if the entire setup is insulated against the surrounding).