Question

Draw a neat, labelled diagram of a suspended coil type moving coil galvanometer. The initial pressure and volume of a gas enclosed in a cylinder are 2 × 10^5 N/m² and 6 × 10^{-3} m³ respectively. If the work done in compressing the gas at constant pressure is 150 J, find the final volume of the gas.

Hint:

Galvanometer detects current via torque on coil in magnetic field; work at constant P is PΔV.

Answer 1

i. Diagram: 

Labelled parts: Coil, N-pole, S-pole, Suspension. 
ii. Final Volume: 
Constant pressure compression: Work done \( W = P \Delta V \), where \( \Delta V = V_i - V_f \) (since compression, \( W>0 \)). 
 
For compression at constant P: \( W = P (V_i - V_f) \). 
\[ 150 = 2 \times 10^5 \times (6 \times 10^{-3} - V_f) \quad \Rightarrow \quad 6 \times 10^{-3} - V_f = \frac{150}{2 \times 10^5} = 7.5 \times 10^{-4}. \] \[ V_f = 6 \times 10^{-3} - 7.5 \times 10^{-4} = 5.25 \times 10^{-3} \, \text{m}^3. \] {Answer: Final volume = 5.25 × 10^{-3} m³.}