Question 1

Why does the photoelectric effect show the particle nature of light?

Accepted Answer

The emission threshold and the linear dependence of Kmax on frequency show that light transfers energy in discrete packets called photons. One incident photon interacts with one electron in this model, and an electron can escape only when the photon has enough energy to overcome the metal's work function.

Question 2

Why does increasing intensity not cause emission below the threshold frequency?

Accepted Answer

Below threshold, each photon has less energy than the work function, so additional photons cannot collectively remove one electron in the photon model. Raising intensity increases the number of incident photons per second, but it does not increase the energy of any individual photon.

Question 3

What is the threshold frequency?

Accepted Answer

The threshold frequency ν₀ is the boundary for a given metal, related to the work function by ν₀ = φ/h. At exactly ν = ν₀, Kmax is zero and no finite photoelectric current is shown; emission occurs for ν > ν₀.

Question 4

How is the stopping potential measured?

Accepted Answer

The collector is made negative relative to the emitter, creating a retarding electric field. Its applied negative magnitude is increased until the fastest photoelectrons are stopped and the photocurrent becomes zero. At that exact point, eV₀ = Kmax; a larger applied voltage keeps the current zero but does not change V₀.

Question 5

How do Kmax and stopping potential depend on frequency and intensity?

Accepted Answer

At fixed intensity, Kmax and stopping potential increase linearly with frequency above threshold, with slopes h and h/e. At fixed frequency above threshold, increasing intensity increases the photon rate and photocurrent but does not change Kmax or stopping potential.

Photoelectric Effect: Knock the Electron Out, Then Trap It

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