Question

The wire made of Phosphor bronze is used as the suspension strip in the moving coil galvanometer, because:

• A. Its restoring torque per unit twist is very large
• B. It is more flexible
• C. It has less tensile strength
• D. Its restoring torque per unit twist is small

Hint:

Lower restoring torque increases sensitivity of galvanometer, hence soft suspension materials are preferred.

Answer 1

The Correct Option is D

Step 1: Understand working of galvanometer.
A moving coil galvanometer works on torque produced due to current and restoring torque of suspension wire.

Step 2: Role of suspension wire.
The suspension wire provides restoring torque to bring the coil back to its original position.

Step 3: Requirement for sensitivity.
For higher sensitivity, even small current should produce large deflection.

Step 4: Relation of restoring torque.
Restoring torque is proportional to twist. Smaller restoring torque gives larger deflection.

Step 5: Property of phosphor bronze.
Phosphor bronze has low torsional rigidity, hence restoring torque per unit twist is small.

Step 6: Conclusion.
This makes the galvanometer more sensitive.

Step 7: Final Answer.
\[ \boxed{\text{Option (D)}} \]