Question

The temperature of a metal coin is increased ny ${100}^0$C and its diameter by 0.15%. Its area increases by nearly

• A. 0.15%
• B. 0.30%
• C. 0.60%
• D. 0.0225%

Answer 1

Answer: (B)

$A=\pi r^2$
$\frac{\Delta A}{A}=2\frac{\Delta A}{r}$
$\frac{\Delta A}{A}$% $=2\left(\frac{\Delta A}{r}\right)\times 100$
$\frac{\Delta A}{A}$% $=2\times 0.15=0.30$%