Time constant is the measure of
a. Response of the system
b. Dislocation of the system from the desired value. c. Adjustment of the system for a given disturbance in the output d. Describes the resistance of the system
Time constant is very important parameters of analysis the system response.
So time constant is measure the speed with which a system can respond to its change.
If time constant is large ,system will take more time to reach the desired value.
If time constant is small, system will take less time to reach the desired value.
Hence time constant is measure response of the system.
Option 'a' is correct.