Photoelectrons are liberated by ultra light of wavelength `2000 Å` from a metallic surface for which the photoelectric threshold is 4000Å. Calculate the de Broglie wavelenth of electrons emitted with maximum kinetic energy.

Explanation

To solve the problem step by step, we will calculate the maximum kinetic energy of the emitted photoelectrons and then use that to find the de Broglie wavelength of the electrons.

### Step 1: Calculate the energy of the incident photons
The energy of the incident photons can be calculated using the formula:
\[ E = \frac{hc}{\lambda} \]
where:
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