Concept:Electrons are bound to their host metal by attractive atomic forces. A rigid energy barrier must be broken to free them.
Formula:$$ E = hf $$
$$ K.E_{max} = hf - hf_0 $$
Solution:- The term \( f_0 \) represents the critical "threshold frequency" specific to that metal.
- If the incoming light's frequency \( f \) is strictly less than \( f_0 \), a single photon will lack the required binding energy to rip an electron out.
- Because quantum interactions are strictly one-to-one (one photon to one electron), no emission can occur, regardless of how intensely the light shines.
Why other options are incorrect:At exactly the threshold frequency, emission
does occur (though electrons emerge with zero kinetic energy). Above the threshold, the effect easily occurs.
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