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Natural ScienceGrade 12Physics

Photoelectric Effect & Einstein's Equation

Understand the quantum nature of electromagnetic radiation, threshold frequency, work function, and kinetic energy of emitted photoelectrons.

Curriculum Learning Competencies
  • Explain the failure of classical wave theory in accounting for the photoelectric effect.
  • Derive and apply Einstein's photoelectric equation: Ek=hf−ΦE_k = hf - \Phi.
  • Interpret stopping potential vs. frequency graphs to determine Planck's constant.
  • Calculate threshold frequency (f0f_0) and threshold wavelength (λ0\lambda_0) for various metal targets.

Essential Formulas & Equations

Einstein's Photoelectric Equation
Kmax⁡=hf−Φ=hcλ−ΦK_{\max} = hf - \Phi = \frac{hc}{\lambda} - \Phi

Where h is Planck's constant (6.626 x 10^-34 J·s) and Phi is the work function.

Threshold Frequency & Work Function
Φ=hf0=hcλ0\Phi = h f_0 = \frac{hc}{\lambda_0}

Minimum photon energy required to liberate an electron from the metal surface.

Stopping Potential Relation
eV0=Kmax⁡=h(f−f0)e V_0 = K_{\max} = h(f - f_0)

Stopping potential is independent of the incident radiation intensity.

Past National Exam Questions

Step-by-step solutions with detailed reasoning

3 Questions Available
Q1ESSLCE National Exam 2015 EC
medium
Monochromatic light of wavelength 400 nm falls on a metal surface whose work function is 2.2 eV. What is the maximum kinetic energy of the emitted photoelectrons? (Take hc=1240 eV⋅nmhc = 1240\text{ eV}\cdot\text{nm})
A
0.9 eV
B
3.1 eV
C
1.8 eV
D
5.3 eV
Q2Grade 12 Physics Model Exam
easy
According to the wave theory of light, which factor was expected to increase the kinetic energy of emitted photoelectrons, contradicting experimental evidence?
A
Light intensity
B
Light frequency
C
Polarization angle
D
Target metal temperature
Q3ESSLCE National Exam 2016 EC
hard
A metal has a threshold frequency of 5.0×1014 Hz5.0 \times 10^{14}\text{ Hz}. If radiation of frequency 8.0×1014 Hz8.0 \times 10^{14}\text{ Hz} is directed onto it, what is the stopping potential V0V_0? (Take h/e=4.14×10−15 V⋅sh/e = 4.14 \times 10^{-15}\text{ V}\cdot\text{s})
A
1.24 V
B
3.31 V
C
0.62 V
D
2.07 V
Interactive Gamified Practice

Master Photoelectric Effect & Einstein's Equation With Interactive Slides

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