How does the photoelectric effect provide evidence for the particle theory of light?

• A. The photoelectric effect shows that light behaves only as a wave and not as a particle.
• B. Electrons are emitted from a metal surface at any frequency of incident light if the intensity is high enough.
• C. Increasing the intensity of light always increases the energy of emitted electrons, regardless of frequency.
• D. Electrons are emitted from a metal surface only when the incident light has a frequency above a certain threshold, regardless of its intensity.

Answer: (D)

Verified step by step guidance

1. Understand the photoelectric effect: When light shines on a metal surface, electrons can be emitted from that surface. This phenomenon is called the photoelectric effect.
2. Recognize the classical wave theory prediction: According to classical wave theory, increasing the intensity (brightness) of light should increase the energy of emitted electrons, and electrons should be emitted at any frequency if the intensity is high enough.
3. Observe the experimental results: Electrons are only emitted if the incident light has a frequency above a certain threshold, regardless of the light's intensity. Increasing intensity below this threshold frequency does not cause electron emission.
4. Interpret the threshold frequency: This suggests that light energy is delivered in discrete packets (quanta) called photons, each with energy \(E = h \times f\), where \(h\) is Planck's constant and \(f\) is the frequency of light.
5. Conclude the evidence for particle theory: Since electrons are emitted only when photons have enough energy (frequency above threshold), the photoelectric effect supports the particle theory of light, showing light behaves as particles (photons) rather than just waves.