Defining the applied voltage V as a function of time

Hi,
I am Naveen doing my MS project "modeling of electrosorption" at Hindustan Unilever R&D,bangalore.In my problem i want to define V=0 at time t=0s and V=V0 at time t>0.Here +V0 is the applied voltage for positive electrode and -V0 is for negative electrode (ex +1.5V and -1.5V) and time t is (0,0.1,1).So how can i define this condition in comsol ?
Could any one pls help me for this.Thanks in advance



Naveen A