Write Einstein’s photoelectric equation. Define the threshold frequency `v_(0)` and stopping potential `V_(0)`.

Explanation

### Step-by-Step Solution

1. **Einstein's Photoelectric Equation**:
The photoelectric effect describes the emission of electrons from a material when it is exposed to light. Einstein formulated this phenomenon with the following equation:
\[ E_k = h\nu - h\nu_0 \]
where:
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