Question

A PMMC instrument is spring controlled. The control stiffness decreases by 0.02 percent per degree Celsius rise in temperature and magnetic field strength decreases by 0.01 percent per degree Celsius rise in temperature. If the rise in temperature is ${10}^{o}C,$ the instrument's reading

• A. decreases by 0.1 percent.
• B. increases by 0.2 percent.
• C. increases by 0.1 percent
• D. decreases by 0.2 percent

Answer 1

The correct option is C increases by 0.1 percent

The change in stiffness of control spring for per degree Celsius rise in temperature $=0.02\%$

The change in magnetic field strength for per degree Celsius rise in temperature $=0.01\%$

$\therefore$ The % increase in deflection
$=0.02\%-0.01\%$
$=0.01\%$

$\text{For}{10}^{o}C\text{rise, the deflection increases by}$
$=0.010\%\times 10=0.1\%$