Question

the pressure of a gas filled in the bulb of a constant volume gas thermometer at 0 and 100 degrees C are 28.6cms and 36.6cms of mercury respectively. the temperature of the bulb at which the pressure will be 35cms of mercury will be how much

Answer 1

In a constant volume gas thermometer, the pressure of the gas varies in proportion to the temperature of the gas. The temperature varies linearly wrt to the pressure and vice versa.

 So the formula is:    T = (P - P₀) / (P₁₀₀ - P₀)  * 100 ⁰C
     Where T is the temperature at pressure P.
                P₀ is pressure at T₀ = 0⁰ C
             and P₁₀₀ is pressure at T₁₀₀ = 100⁰C
                
   T = (35.0 - 28.6) / (36.6 - 28.6)  * 100 ⁰C 
       = 80⁰ C

Answer 2

80 degree Celsius = T