In simple pendulum, when bob is in deflection position, the tension in the string is `T=mgcostheta`. Since, the value of `theta` is differenet at different positions, hence tension in the string is not constant throughout the oscillation. (a) At end points, `theta` is maximum : the value of `costheta` is least, hence the value of tension in the string is least. (b) At th emean position, the value of `theta=0^(@)` and `cos0^(@)=1`, so the value of thension is greatest.
