Question

For photoelectric emission, tungsten requires light of 2300 $\mathring{A}$ . If light of 1800 $\mathring{A}$ wavelength is incident then emission

• A. takes place
• B. doesn't take place
• C. may or may not take place
• D. depends on frequency

Answer 1

Answer: (A)

If kinetic energy of photoelectrons emitted from metal surface is $E_k$ and $W$ is the energy required to eject photoelectrons from the metal, then from Einstein's photoelectric equation
$E_k=hv-W$
Also, $E=\frac{hc}{\lambda }$
where $h$ is Planck's constant and $c$ is speed of light and $\lambda$ is wavelength.
Since wavelength is reduced from $2300\mathring{A}$ to $1800\mathring{A}$, energy increases hence emission takes place.