# Kinetic energy of the released particle

**Question**

Work function of a material varies with time as !!phi= phi_0(2+sin[(pi t)/2])!!.

Plot !!KE_(max)!! vs time.

*energy of incident photons: !!2.5 phi_0!!

(a)

(b)

(c)

(d)

**Solution**

We know that,

!!KE_(max)="Energy of incident photons"- "Work funtion"!!

According to question,

!!=> KE_(max)= 2.5 phi_0- phi_0(2+sin((pit)/2))!!

!!=> KE_(max)= 0.5 phi_0 - phi_0 sin((pit)/2)!!

Therefore when !!t=0!!, !!KE_(max)= 0.5 phi_0!!

The electron is released only if !! 0.5 phi_0 - phi_0 sin((pit)/2)>0!!

!!KE_(max)!! can't be negative. So, option (a) and (d) is not possible.

It will behave like a **sin** function. Option (c) is correct.