# Acceleration due to gravity using Rod pendulum

Period of oscillations of a pendulum depends on it's length and the value of gravity. Period of oscillation of a uniform rod about one end is given by T= 2π√(2l⁄ 3g), where l is the length and g is the acceleration due to gravity.

# Objective

Measure the period of oscillations of a rod pendulum using a photo-transisor and LED arrangement. The pendulum (T-shaped, a knife edge attached to a 6mm dia rod) is made to swing between an LED and photo-transistor, connected to expEYES. The LED and photo-transistor are mounted on a U-shaped bracket as shown in figure.

# Procedure

- Oscillate the pendulum and click on START
- Repeat with different pendulum lengths.

# Discussion

The period of oscillation can be measured with an accuracy of 100 microseconds. However mainly there are two sources of error. The length is measured from the knife edge to the bottom and used in the formula. But there is a small mass projecting above the knife edge that is not included in the calculation. Also the calculations assume that the pendulum must be exactly vertical in the resting position, which has to be ensured.