The maximum KE of photoelectrons emitted from a cetain metallic surface is 30 eV when monochromatic radiation of wavelength `lamda` falls on it. When the same surface is illuminated with light of wavelength `2lamda`, the minimum KE of photoelectrons is found to be 10 eV. (a) Calculate the wavelength `lamda` and (b) determine the maximum wavelength of incident radiation for which photoelectric emission is possible.

Explanation

To solve the problem step by step, we will use Einstein's photoelectric equation, which relates the energy of the incident photons to the work function of the metal and the kinetic energy of the emitted photoelectrons.

### Step 1: Write down Einstein's photoelectric equation
The equation is given by:
\[ E = W + KE \]
Where:
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