Question

The measurement value of length of a simple pendulum is 20 cm with 2 mm accuracy. The time taken for 50 oscillations was measured to be 40 s within 1 s resolution. Calculate the percentage accuracy in the determination of acceleration due to gravity from the above measurement

Answer 1

Consider, t is time and n is number of revolutions.

Therefore, T = t/n.

Hence, ∆T = ∆t/n; n is a constant term.

On simplifying we get, ∆T/T = ∆t/t, let this be equation 1.

We know that, T = 2π√(l/g)

By squaring both the sides,

T² = 4π²l/g ⇒ g = 4π²l/T²

Therefore, ∆g/g = ∆l/l + 2∆T/T

This implies that, ∆g/g = ∆l/l + 2∆t/t……. from equation 1.

Therefore, percentage error in g = ( ∆l/l + 2∆t/t) X 100

We have, ∆l = 1mm = 0.1 cm , l = 20cm

∆t = 1 s and t = 90 s

Therefore, % error in g = (0.1/20 + 2 × 1/90) X 100 = ( 0.005 + 0.022) 100 = (0.027) 100 = 2.7%