Question

In a simple pendulum experiment for determination of acceleration due to gravity (g), time taken for $20$ oscillations is measured by using a watch of $1$ second least count. The mean value of time taken comes out to be $30\, s$. The length of pendulum is measured by using a meter scale of least count $1\, mm$ and the value obtained is $55.0\, cm$. The percentage error in the determination of $g$ is close to :

• A. 0.70%
• B. 0.20%
• C. 3.50%
• D. 6.80%

Answer 1

Answer: (D)

6.80%

Answer 2

$T = \frac{30 \sec}{20} \Delta T = \frac{1}{20} \sec$
$L = 55 cm \Delta L = 1 mm = 0.1 cm$
$g = \frac{4\pi^{2}L}{T^{2}}$
percentage error in g is
$\frac{\Delta g}{g} \times100\% = \left(\frac{\Delta L}{L} + \frac{2\Delta T}{T}\right) 100\%$
$= \left(\frac{0.1 }{55} + \frac{2\left(\frac{1}{20}\right)}{\frac{30}{20}}\right) 100\% \simeq 6.8 \%$