In the photoelectric effect, what condition must be met for electrons to be emitted?

In the photoelectric effect, what condition must be met for electrons to be emitted?

• A. The photon energy hf must be at least the work function φ; hf ≥ φ
• B. The photon energy hf must be less than φ
• C. The photon energy hf must be zero
• D. The work function φ must be greater than hf

Answer: (A)