In a photoelectric experiment using a sodium surface, you find a stopping potential of 1.85 V for a wavelength of 300 nm and a stopping potential of 0.820 V for a wavelength of 400 nm. From these data find (a) a value for the Planck constant, (b) the work function `Phi` for sodium, and (c) the cutoff wavelength `lambda_(0)` for sodium.

Explanation

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

### Step 1: Understanding the Photoelectric Effect
According to Einstein's photoelectric equation:
\[ E = \Phi + KE \]
Where:
- \( E \) is the energy of the incoming photon,
- \( \Phi \) is the work function of the material,
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