Physics

Problem

In a photoelectric experiment on an unknown metal, the following observations were recorded: • For incident light of frequency

6.0\times10^{14}\,\text{Hz}

, the stopping potential was

0.50\,\text{V}

. • For incident light of frequency

8.0\times10^{14}\,\text{Hz}

, the stopping potential was

2.10\,\text{V}

. a. (i) Using the above data, calculate the numerical value of Planck’s constant. b. (ii) Determine the threshold frequency of the metal. c. (iii) Hence find the minimum energy, in electron-volt, required to liberate an electron from the metal surface. (Take

e = 1.6\times10^{-19}\,\text{C}

Intuitive explanation

The photoelectric effect reveals a linear relationship between light frequency and the kinetic energy of ejected electrons—this is Einstein's key insight. By using the stopping potential (which directly measures maximum kinetic energy), you can extract two unknowns: the work function of the metal and Planck's constant. Set up two equations from $eV_s = hf - \phi$ for each frequency, then solve the system by subtraction to find $h$ , and back-substitute to find $\phi$ .

Intuitive explanation

Browse the problem library