As illustrated in the figure, a lady wears an ear-ring suspended by...

The ear-ring suspended by a light wire can be considered as a simple pendulum.

The time period $T$ of small oscillations for a simple pendulum is given by:

$T = 2\pi \sqrt{\dfrac{L}{g}}$

Given:
Length of the wire, $L = 3 \text{ cm} = 0.03 \text{ m}$
Acceleration due to gravity, $g \approx 10 \text{ m/s}^2$

Substituting the values into the formula:

$T = 2\pi \sqrt{\dfrac{0.03}{10}}$

$T = 2 \times 3.14 \times \sqrt{0.003}$

$T \approx 6.28 \times 0.0547$

$T \approx 0.34 \text{ s}$