Question

Which of the following has a uniform scale ?

• A. Spring Control
• B. Gravity Control
• C. Air Damping
• D. Eddy current damping

Hint:

Spring control gives: \[ T_c \propto \theta \] Hence equal pointer movements correspond to equal measured increments, producing a uniform scale.

Answer 1

The Correct Option is A

Concept: In indicating instruments, controlling torque determines how the pointer settles at a steady reading. Two common controlling methods are:
• Spring control,
• Gravity control. Among these:
• Spring control provides a uniform scale,
• Gravity control provides a non-uniform scale. Damping methods do not determine scale uniformity.

Step 1: Understanding spring control. In spring control: \[ T_c \propto \theta \] where:
• \(T_c\) is controlling torque,
• \(\theta\) is deflection angle. Since torque is directly proportional to deflection: \[ \theta \propto \text{measured quantity} \] Thus equal increments produce equal deflections. Hence the scale becomes uniform.

Step 2: Understanding gravity control. In gravity control: \[ T_c \propto \sin\theta \] Since sine relation is nonlinear:
• deflections are not equally spaced,
• scale becomes non-uniform.

Step 3: Understanding damping methods. Air damping and eddy current damping only help:
• reduce oscillations,
• settle the pointer quickly. They do not affect scale uniformity.

Step 4: Checking each option carefully.
• Option \(1\): Spring Control \(\rightarrow\) Correct
• Option \(2\): Gravity Control \(\rightarrow\) Non-uniform scale
• Option \(3\): Air Damping \(\rightarrow\) Damping method only
• Option \(4\): Eddy current damping \(\rightarrow\) Damping method only Thus the correct answer is: \[ \boxed{(1)\; \text{Spring Control}} \]