With reference to photo-electric effect, what is meant by threshold wavelength ?

Explanation

**Step-by-Step Solution:**

1. **Understanding the Photoelectric Effect**: The photoelectric effect refers to the phenomenon where electrons are emitted from a material (usually a metal) when it is exposed to light (or electromagnetic radiation) of sufficient energy.

2. **Energy of Photons**: The energy of a photon is given by the equation:
\[ E = \frac{hc}{\lambda} \]
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