Question

When the energy of the incident radiation is increased by $20\%$ the kinetic energy of the photoelectrons emitted from a metal surface increased from $0.5\text{eV}$ to $0.8\text{eV}$. The work functions of the metal is-

• A. $0.65\text{eV}$
• B. $1.0\text{eV}$
• C. $1.3\text{eV}$
• D. $1.5\text{eV}$

Answer 1

The correct option is B $1.0\text{eV}$

By using Einstein's equation
$hv={\varphi }_0+K{E}_{max}$

We have
$hv={\varphi }_0+0.5....\left(i\right)$
$1.2hv={\varphi }_0+0.8....\left(ii\right)$

On dividing the equations,
$1.2=\frac{\varphi +0.8}{\varphi +0.5}$
$1.2{\varphi }_0+0.6={\varphi }_0+0.8$
$0.2{\varphi }_0=0.2$
${\varphi }_0=1\text{eV}$