Question

In photoelectric effect, if the energy required to overcome the attractive forces on the electron (work functions) of $Li,Na$ and $Rb$ are $2.41eV,2.30eV$ and $2.09eV$ respectively, the work function of ${}^{\prime }{K}^{\prime }$ could approximately be (in $eV$):

• A. $2.52$
• B. $2.20$
• C. $2.35$
• D. $2.01$

Answer 1

Answer: (B)

$2.20$

The photoelectric work function of potassium is 2.20 eV.

As we go down the group the work function of the alkali metals decreases. $Li$ has 2.41, $Na$ has 2.30 eV and $Rb$ has 2.09 eV.

As just below the $Na$, there is $K$ in the first group (alkali metals) and below the $K$ there is $Rb$ so the $K$ must have a work function in between the $Na$ and $Rb$.