While deriving the equation of time period for simple pendulum which quantity should be kept small:

Explanation

(a) Length of a simple pendulum: The length of a simple pendulum does affect the time period, but it doesn't need to be kept small. In fact, the time period of a simple pendulum is directly proportional to the square root of the length. So, this option is not correct. (b) Amplitude: The correct option! When deriving the equation for the time period of a simple pendulum, it is assumed that the amplitude (the maximum angle of swing) is small. This assumption allows for a linear approximation of the restoring force, which simplifies the mathematical analysis. (c) Mass of simple pendulum: The mass of the simple pendulum does not affect the time period. The time period of a simple pendulum depends only on the length and the acceleration due to gravity. So, this option is not correct. (d) Gravitational acceleration: The gravitational acceleration, denoted by "g," does affect the time period of a simple pendulum. However, it is a constant value on Earth (approximately 9.8 m/s^2), and it doesn't need to be kept small. So, this option is not correct.