Photoelectric Effect

Q: If the intensity of light is doubled while keeping the frequency constant, what happens to the maximum kinetic energy of the emitted electrons?

It remains the same The kinetic energy of individual electrons depends ONLY on the photon frequency (hf) and the work function. Intensity only affects the number of photons hitting the surface per unit time, which increases the rate of emission (current) but not individual electron energy.

Q: What is the threshold frequency for a metal with a work function of 2.0 eV?

4.8 imes 10^{14} Hz Using hf_0 = Phi, f_0 = Phi/h = (2.0 imes 1.6 imes 10^{-19} ext{ J}) / (6.626 imes 10^{-34} ext{ J s}) approx 4.8 imes 10^{14} Hz (visible spectrum).

Experiment with the quantum nature of light. Adjust wavelength, intensity, target metal, and stopping potential to verify the Einstein photoelectric equation.

WHAT IS THE PHOTOELECTRIC EFFECT?

The photoelectric effect is the emission of electrons from a material when light of sufficient frequency (the **threshold frequency**) shines on it. This effect was key to establishing the particle nature of light (photons). According to **Einstein's Photoelectric Equation**, the maximum kinetic energy of the ejected electrons depends on the photon energy minus the **work function** (the energy required to free an electron from the surface).

HOW TO USE THIS VISUALIZATION

1. **Adjust Frequency**: Use the slider to change the light color from red to ultraviolet. Observe that below the threshold frequency , no electrons are ejected regardless of intensity. 2. **Change Intensity**: Note that increasing the brightness increases the *number* of electrons (current) but not their speed. 3. **Select Metal**: Choose different materials (Sodium, Zinc, etc.) to see how their work function affects the threshold frequency.

CORE FORMULAS

Einstein's Photoelectric Equation

Threshold Frequency condition

Stopping potential relationship

AP EXAM CONNECTION

Unit: Unit 7: Quantum, Atomic, and Nuclear Physics (Topic 7.1)
Learning Objective: LO 6.F.3

COMMON MISCONCEPTIONS

Energy of electrons depends on light brightness (it doesn't; it depends on frequency)
There is a time delay between light hitting the metal and emission (emission is instantaneous once the threshold is met)

KEY TAKEAWAYS

The photoelectric effect proves that light behaves like a particle (photon).
Increasing frequency increases the maximum kinetic energy of electrons.
Increasing intensity increases the number of emitted electrons (current).
No electrons are emitted below the threshold frequency.

PRACTICE QUESTIONS

Q1 (CONCEPTUAL): If the intensity of light is doubled while keeping the frequency constant, what happens to the maximum kinetic energy of the emitted electrons?

Show Answer & Explanation

Answer: It remains the same

Explanation: The kinetic energy of individual electrons depends ONLY on the photon frequency () and the work function. Intensity only affects the number of photons hitting the surface per unit time, which increases the rate of emission (current) but not individual electron energy.

Q2 (QUANTITATIVE): What is the threshold frequency for a metal with a work function of 2.0 eV?

Show Answer & Explanation

Answer: Hz

Explanation: Using , Hz (visible spectrum).