Question

in the photoelectric effect, an electric current forms when light strikes a metal surface. which statement explains what causes the current?
a. electrons flow from one atom to another because the light acts as a wave.
b. electrons are destroyed when light strikes a surface because the light acts as particles.
c. the light causes electrons to flow in different directions within an atom because light acts as a wave.
d. electrons are knocked off the surface when light strikes it because the light acts as particles.

Explanation:

In the photoelectric effect, light (acting as particles - photons) strikes a metal surface. The energy of these photons is transferred to electrons. When the photon energy is sufficient (greater than or equal to the work - function of the metal), electrons are ejected (knocked off) from the metal surface. These ejected electrons can then flow and form an electric current.

• Option A: Light acting as a wave cannot explain the photoelectric effect. The wave - theory of light cannot account for the instantaneous ejection of electrons and the threshold frequency in the photoelectric effect.
• Option B: Electrons are not destroyed. They are just ejected from the metal surface.
• Option C: Light acting as a wave cannot explain the photoelectric effect. Also, the electrons are ejected from the atom (not just flowing within the atom in different directions in the context of the photoelectric effect current formation).
• Option D: This is in line with the photon - electron interaction in the photoelectric effect.

Answer:

D. Electrons are knocked off the surface when light strikes it because the light acts as particles.